cpython/Python/ast.c

/*
 * This file includes functions to transform a concrete syntax tree (CST) to
 * an abstract syntax tree (AST).  The main function is PyAST_FromNode().
 *
 */
#include "Python.h"
#include "Python-ast.h"
#include "grammar.h"
#include "node.h"
#include "pyarena.h"
#include "ast.h"
#include "token.h"
#include "parsetok.h"
#include "graminit.h"

#include <assert.h>

/* XXX TO DO
   - re-indent this file (should be done)
   - internal error checking (freeing memory, etc.)
   - syntax errors
*/

/* Data structure used internally */
struct compiling {
    char *c_encoding; /* source encoding */
    PyArena *c_arena; /* arena for allocating memeory */
};

static asdl_seq *seq_for_testlist(struct compiling *, const node *);
static expr_ty ast_for_expr(struct compiling *, const node *);
static stmt_ty ast_for_stmt(struct compiling *, const node *);
static asdl_seq *ast_for_suite(struct compiling *, const node *);
static asdl_seq *ast_for_exprlist(struct compiling *, const node *, int);
static expr_ty ast_for_testlist(struct compiling *, const node *);
static expr_ty ast_for_testlist_gexp(struct compiling *, const node *);

/* Note different signature for ast_for_call */
static expr_ty ast_for_call(struct compiling *, const node *, expr_ty);

static PyObject *parsenumber(const char *);
static PyObject *parsestr(const char *s, const char *encoding);
static PyObject *parsestrplus(struct compiling *, const node *n);

#ifndef LINENO
#define LINENO(n)	((n)->n_lineno)
#endif

static identifier
new_identifier(const char* n, PyArena *arena) {
    PyObject* id = PyString_InternFromString(n);
    PyArena_AddPyObject(arena, id);
    return id;
}

#define NEW_IDENTIFIER(n) new_identifier(STR(n), c->c_arena)

/* This routine provides an invalid object for the syntax error.
   The outermost routine must unpack this error and create the
   proper object.  We do this so that we don't have to pass
   the filename to everything function.

   XXX Maybe we should just pass the filename...
*/

static int
ast_error(const node *n, const char *errstr)
{
    PyObject *u = Py_BuildValue("zi", errstr, LINENO(n));
    if (!u)
	return 0;
    PyErr_SetObject(PyExc_SyntaxError, u);
    Py_DECREF(u);
    return 0;
}

static void
ast_error_finish(const char *filename)
{
    PyObject *type, *value, *tback, *errstr, *loc, *tmp;
    long lineno;

    assert(PyErr_Occurred());
    if (!PyErr_ExceptionMatches(PyExc_SyntaxError))
	return;

    PyErr_Fetch(&type, &value, &tback);
    errstr = PyTuple_GetItem(value, 0);
    if (!errstr)
	return;
    Py_INCREF(errstr);
    lineno = PyInt_AsLong(PyTuple_GetItem(value, 1));
    if (lineno == -1) {
	Py_DECREF(errstr);
	return;
    }
    Py_DECREF(value);

    loc = PyErr_ProgramText(filename, lineno);
    if (!loc) {
	Py_INCREF(Py_None);
	loc = Py_None;
    }
    tmp = Py_BuildValue("(zlOO)", filename, lineno, Py_None, loc);
    Py_DECREF(loc);
    if (!tmp) {
	Py_DECREF(errstr);
	return;
    }
    value = Py_BuildValue("(OO)", errstr, tmp);
    Py_DECREF(errstr);
    Py_DECREF(tmp);
    if (!value)
	return;
    PyErr_Restore(type, value, tback);
}

/* num_stmts() returns number of contained statements.

   Use this routine to determine how big a sequence is needed for
   the statements in a parse tree.  Its raison d'etre is this bit of
   grammar:

   stmt: simple_stmt | compound_stmt
   simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE

   A simple_stmt can contain multiple small_stmt elements joined
   by semicolons.  If the arg is a simple_stmt, the number of
   small_stmt elements is returned.
*/

static int
num_stmts(const node *n)
{
    int i, l;
    node *ch;

    switch (TYPE(n)) {
        case single_input:
            if (TYPE(CHILD(n, 0)) == NEWLINE)
                return 0;
            else
                return num_stmts(CHILD(n, 0));
        case file_input:
            l = 0;
            for (i = 0; i < NCH(n); i++) {
                ch = CHILD(n, i);
                if (TYPE(ch) == stmt)
                    l += num_stmts(ch);
            }
            return l;
        case stmt:
            return num_stmts(CHILD(n, 0));
        case compound_stmt:
            return 1;
        case simple_stmt:
            return NCH(n) / 2; /* Divide by 2 to remove count of semi-colons */
        case suite:
            if (NCH(n) == 1)
                return num_stmts(CHILD(n, 0));
            else {
                l = 0;
                for (i = 2; i < (NCH(n) - 1); i++)
                    l += num_stmts(CHILD(n, i));
                return l;
            }
        default: {
            char buf[128];

            sprintf(buf, "Non-statement found: %d %d\n",
                    TYPE(n), NCH(n));
            Py_FatalError(buf);
        }
    }
    assert(0);
    return 0;
}

/* Transform the CST rooted at node * to the appropriate AST
*/

mod_ty
PyAST_FromNode(const node *n, PyCompilerFlags *flags, const char *filename,
               PyArena *arena)
{
    int i, j, k, num;
    asdl_seq *stmts = NULL;
    stmt_ty s;
    node *ch;
    struct compiling c;

    if (flags && flags->cf_flags & PyCF_SOURCE_IS_UTF8) {
        c.c_encoding = "utf-8";
    } else if (TYPE(n) == encoding_decl) {
        c.c_encoding = STR(n);
        n = CHILD(n, 0);
    } else {
        c.c_encoding = NULL;
    }
    c.c_arena = arena;

    k = 0;
    switch (TYPE(n)) {
        case file_input:
            stmts = asdl_seq_new(num_stmts(n), arena);
            if (!stmts)
                    return NULL;
            for (i = 0; i < NCH(n) - 1; i++) {
                ch = CHILD(n, i);
                if (TYPE(ch) == NEWLINE)
                    continue;
                REQ(ch, stmt);
                num = num_stmts(ch);
                if (num == 1) {
                    s = ast_for_stmt(&c, ch);
                    if (!s)
                        goto error;
                    asdl_seq_SET(stmts, k++, s);
                }
                else {
                    ch = CHILD(ch, 0);
                    REQ(ch, simple_stmt);
                    for (j = 0; j < num; j++) {
                        s = ast_for_stmt(&c, CHILD(ch, j * 2));
                        if (!s)
                            goto error;
                        asdl_seq_SET(stmts, k++, s);
                    }
                }
            }
            return Module(stmts, arena);
        case eval_input: {
            expr_ty testlist_ast;

            /* XXX Why not gen_for here? */
            testlist_ast = ast_for_testlist(&c, CHILD(n, 0));
            if (!testlist_ast)
                goto error;
            return Expression(testlist_ast, arena);
        }
        case single_input:
            if (TYPE(CHILD(n, 0)) == NEWLINE) {
                stmts = asdl_seq_new(1, arena);
                if (!stmts)
		    goto error;
                asdl_seq_SET(stmts, 0, Pass(n->n_lineno, n->n_col_offset, arena));
                return Interactive(stmts, arena);
            }
            else {
                n = CHILD(n, 0);
                num = num_stmts(n);
                stmts = asdl_seq_new(num, arena);
                if (!stmts)
		    goto error;
                if (num == 1) {
		    s = ast_for_stmt(&c, n);
		    if (!s)
			goto error;
                    asdl_seq_SET(stmts, 0, s);
                }
                else {
                    /* Only a simple_stmt can contain multiple statements. */
                    REQ(n, simple_stmt);
                    for (i = 0; i < NCH(n); i += 2) {
                        if (TYPE(CHILD(n, i)) == NEWLINE)
                            break;
                        s = ast_for_stmt(&c, CHILD(n, i));
                        if (!s)
                            goto error;
                        asdl_seq_SET(stmts, i / 2, s);
                    }
                }

                return Interactive(stmts, arena);
            }
        default:
            goto error;
    }
 error:
    ast_error_finish(filename);
    return NULL;
}

/* Return the AST repr. of the operator represented as syntax (|, ^, etc.)
*/

static operator_ty
get_operator(const node *n)
{
    switch (TYPE(n)) {
        case VBAR:
            return BitOr;
        case CIRCUMFLEX:
            return BitXor;
        case AMPER:
            return BitAnd;
        case LEFTSHIFT:
            return LShift;
        case RIGHTSHIFT:
            return RShift;
        case PLUS:
            return Add;
        case MINUS:
            return Sub;
        case STAR:
            return Mult;
        case SLASH:
            return Div;
        case DOUBLESLASH:
            return FloorDiv;
        case PERCENT:
            return Mod;
        default:
            return 0;
    }
}

/* Set the context ctx for expr_ty e, recursively traversing e.

   Only sets context for expr kinds that "can appear in assignment context"
   (according to ../Parser/Python.asdl).  For other expr kinds, it sets
   an appropriate syntax error and returns false.
*/

static int
set_context(expr_ty e, expr_context_ty ctx, const node *n)
{
    asdl_seq *s = NULL;
    /* If a particular expression type can't be used for assign / delete,
       set expr_name to its name and an error message will be generated.
    */
    const char* expr_name = NULL;

    /* The ast defines augmented store and load contexts, but the
       implementation here doesn't actually use them.  The code may be
       a little more complex than necessary as a result.  It also means
       that expressions in an augmented assignment have no context.
       Consider restructuring so that augmented assignment uses
       set_context(), too.
    */
    assert(ctx != AugStore && ctx != AugLoad);

    switch (e->kind) {
        case Attribute_kind:
	    if (ctx == Store &&
		    !strcmp(PyString_AS_STRING(e->v.Attribute.attr), "None")) {
		    return ast_error(n, "assignment to None");
	    }
	    e->v.Attribute.ctx = ctx;
	    break;
        case Subscript_kind:
	    e->v.Subscript.ctx = ctx;
	    break;
        case Name_kind:
	    if (ctx == Store &&
		!strcmp(PyString_AS_STRING(e->v.Name.id), "None")) {
		    return ast_error(n, "assignment to None");
	    }
	    e->v.Name.ctx = ctx;
	    break;
        case List_kind:
	    e->v.List.ctx = ctx;
	    s = e->v.List.elts;
	    break;
        case Tuple_kind:
            if (asdl_seq_LEN(e->v.Tuple.elts) == 0) 
                return ast_error(n, "can't assign to ()");
	    e->v.Tuple.ctx = ctx;
	    s = e->v.Tuple.elts;
	    break;
        case Lambda_kind:
            expr_name = "lambda";
            break;
        case Call_kind:
            expr_name = "function call";
	    break;
        case BoolOp_kind:
        case BinOp_kind:
        case UnaryOp_kind:
            expr_name = "operator";
            break;
        case GeneratorExp_kind:
            expr_name = "generator expression";
            break;
        case ListComp_kind:
            expr_name = "list comprehension";
            break;
        case Dict_kind:
        case Num_kind:
        case Str_kind:
            expr_name = "literal";
            break;
        case Compare_kind:
            expr_name = "comparison";
            break;
        case Repr_kind:
            expr_name = "repr";
            break;
        default:
            PyErr_Format(PyExc_SystemError, 
                         "unexpected expression in assignment %d (line %d)", 
                         e->kind, e->lineno);
            return 0;
    }
    /* Check for error string set by switch */
    if (expr_name) {
        char buf[300];
        PyOS_snprintf(buf, sizeof(buf),
                      "can't %s %s",
                      ctx == Store ? "assign to" : "delete",
                      expr_name);
        return ast_error(n, buf);
    }

    /* If the LHS is a list or tuple, we need to set the assignment
       context for all the contained elements.  
    */
    if (s) {
	int i;

	for (i = 0; i < asdl_seq_LEN(s); i++) {
	    if (!set_context(asdl_seq_GET(s, i), ctx, n))
		return 0;
	}
    }
    return 1;
}

static operator_ty
ast_for_augassign(const node *n)
{
    REQ(n, augassign);
    n = CHILD(n, 0);
    switch (STR(n)[0]) {
        case '+':
            return Add;
        case '-':
            return Sub;
        case '/':
            if (STR(n)[1] == '/')
                return FloorDiv;
            else
                return Div;
        case '%':
            return Mod;
        case '<':
            return LShift;
        case '>':
            return RShift;
        case '&':
            return BitAnd;
        case '^':
            return BitXor;
        case '|':
            return BitOr;
        case '*':
            if (STR(n)[1] == '*')
                return Pow;
            else
                return Mult;
        default:
            PyErr_Format(PyExc_SystemError, "invalid augassign: %s", STR(n));
            return 0;
    }
}

static cmpop_ty
ast_for_comp_op(const node *n)
{
    /* comp_op: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in'|'is'
               |'is' 'not'
    */
    REQ(n, comp_op);
    if (NCH(n) == 1) {
	n = CHILD(n, 0);
	switch (TYPE(n)) {
            case LESS:
                return Lt;
            case GREATER:
                return Gt;
            case EQEQUAL:			/* == */
                return Eq;
            case LESSEQUAL:
                return LtE;
            case GREATEREQUAL:
                return GtE;
            case NOTEQUAL:
                return NotEq;
            case NAME:
                if (strcmp(STR(n), "in") == 0)
                    return In;
                if (strcmp(STR(n), "is") == 0)
                    return Is;
            default:
                PyErr_Format(PyExc_SystemError, "invalid comp_op: %s",
                             STR(n));
                return 0;
	}
    }
    else if (NCH(n) == 2) {
	/* handle "not in" and "is not" */
	switch (TYPE(CHILD(n, 0))) {
            case NAME:
                if (strcmp(STR(CHILD(n, 1)), "in") == 0)
                    return NotIn;
                if (strcmp(STR(CHILD(n, 0)), "is") == 0)
                    return IsNot;
            default:
                PyErr_Format(PyExc_SystemError, "invalid comp_op: %s %s",
                             STR(CHILD(n, 0)), STR(CHILD(n, 1)));
                return 0;
	}
    }
    PyErr_Format(PyExc_SystemError, "invalid comp_op: has %d children",
                 NCH(n));
    return 0;
}

static asdl_seq *
seq_for_testlist(struct compiling *c, const node *n)
{
    /* testlist: test (',' test)* [','] */
    asdl_seq *seq;
    expr_ty expression;
    int i;
    assert(TYPE(n) == testlist
	   || TYPE(n) == listmaker
	   || TYPE(n) == testlist_gexp
	   || TYPE(n) == testlist_safe
	   );

    seq = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
    if (!seq)
        return NULL;

    for (i = 0; i < NCH(n); i += 2) {
        assert(TYPE(CHILD(n, i)) == test || TYPE(CHILD(n, i)) == old_test);

        expression = ast_for_expr(c, CHILD(n, i));
        if (!expression)
            return NULL;

        assert(i / 2 < seq->size);
        asdl_seq_SET(seq, i / 2, expression);
    }
    return seq;
}

static expr_ty
compiler_complex_args(struct compiling *c, const node *n)
{
    int i, len = (NCH(n) + 1) / 2;
    expr_ty result;
    asdl_seq *args = asdl_seq_new(len, c->c_arena);
    if (!args)
        return NULL;

    REQ(n, fplist);
    for (i = 0; i < len; i++) {
        const node *child = CHILD(CHILD(n, 2*i), 0);
        expr_ty arg;
        if (TYPE(child) == NAME) {
    		if (!strcmp(STR(child), "None")) {
	    		ast_error(child, "assignment to None");
		    	return NULL;
		    }   
            arg = Name(NEW_IDENTIFIER(child), Store, LINENO(child), child->n_col_offset,
                       c->c_arena);
	    }
        else {
            arg = compiler_complex_args(c, CHILD(CHILD(n, 2*i), 1));
        }
        asdl_seq_SET(args, i, arg);
    }

    result = Tuple(args, Store, LINENO(n), n->n_col_offset, c->c_arena);
    if (!set_context(result, Store, n))
        return NULL;
    return result;
}


/* Create AST for argument list. */

static arguments_ty
ast_for_arguments(struct compiling *c, const node *n)
{
    /* parameters: '(' [varargslist] ')'
       varargslist: (fpdef ['=' test] ',')* ('*' NAME [',' '**' NAME]
            | '**' NAME) | fpdef ['=' test] (',' fpdef ['=' test])* [',']
    */
    int i, j, k, n_args = 0, n_defaults = 0, found_default = 0;
    asdl_seq *args, *defaults;
    identifier vararg = NULL, kwarg = NULL;
    node *ch;

    if (TYPE(n) == parameters) {
	if (NCH(n) == 2) /* () as argument list */
	    return arguments(NULL, NULL, NULL, NULL, c->c_arena);
	n = CHILD(n, 1);
    }
    REQ(n, varargslist);

    /* first count the number of normal args & defaults */
    for (i = 0; i < NCH(n); i++) {
	ch = CHILD(n, i);
	if (TYPE(ch) == fpdef)
	    n_args++;
	if (TYPE(ch) == EQUAL)
	    n_defaults++;
    }
    args = (n_args ? asdl_seq_new(n_args, c->c_arena) : NULL);
    if (!args && n_args)
    	return NULL; /* Don't need to go to NULL; nothing allocated */
    defaults = (n_defaults ? asdl_seq_new(n_defaults, c->c_arena) : NULL);
    if (!defaults && n_defaults)
        goto error;

    /* fpdef: NAME | '(' fplist ')'
       fplist: fpdef (',' fpdef)* [',']
    */
    i = 0;
    j = 0;  /* index for defaults */
    k = 0;  /* index for args */
    while (i < NCH(n)) {
	ch = CHILD(n, i);
	switch (TYPE(ch)) {
            case fpdef:
                /* XXX Need to worry about checking if TYPE(CHILD(n, i+1)) is
                   anything other than EQUAL or a comma? */
                /* XXX Should NCH(n) check be made a separate check? */
                if (i + 1 < NCH(n) && TYPE(CHILD(n, i + 1)) == EQUAL) {
                    asdl_seq_SET(defaults, j++, 
				    ast_for_expr(c, CHILD(n, i + 2)));
                    i += 2;
		    found_default = 1;
                }
		else if (found_default) {
		    ast_error(n, 
			     "non-default argument follows default argument");
		    goto error;
		}
                if (NCH(ch) == 3) {
                    asdl_seq_SET(args, k++, 
                                    compiler_complex_args(c, CHILD(ch, 1))); 
		}
                else if (TYPE(CHILD(ch, 0)) == NAME) {
		    expr_ty name;
		    if (!strcmp(STR(CHILD(ch, 0)), "None")) {
			    ast_error(CHILD(ch, 0), "assignment to None");
			    goto error;
		    }
                    name = Name(NEW_IDENTIFIER(CHILD(ch, 0)),
                                Param, LINENO(ch), ch->n_col_offset, c->c_arena);
                    if (!name)
                        goto error;
                    asdl_seq_SET(args, k++, name);
					 
		}
                i += 2; /* the name and the comma */
                break;
            case STAR:
		if (!strcmp(STR(CHILD(n, i+1)), "None")) {
			ast_error(CHILD(n, i+1), "assignment to None");
			goto error;
		}
                vararg = NEW_IDENTIFIER(CHILD(n, i+1));
                i += 3;
                break;
            case DOUBLESTAR:
		if (!strcmp(STR(CHILD(n, i+1)), "None")) {
			ast_error(CHILD(n, i+1), "assignment to None");
			goto error;
		}
                kwarg = NEW_IDENTIFIER(CHILD(n, i+1));
                i += 3;
                break;
            default:
                PyErr_Format(PyExc_SystemError,
                             "unexpected node in varargslist: %d @ %d",
                             TYPE(ch), i);
                goto error;
	}
    }

    return arguments(args, vararg, kwarg, defaults, c->c_arena);

 error:
    Py_XDECREF(vararg);
    Py_XDECREF(kwarg);
    return NULL;
}

static expr_ty
ast_for_dotted_name(struct compiling *c, const node *n)
{
    expr_ty e;
    identifier id;
    int lineno, col_offset;
    int i;

    REQ(n, dotted_name);

    lineno = LINENO(n);
    col_offset = n->n_col_offset;

    id = NEW_IDENTIFIER(CHILD(n, 0));
    if (!id)
        return NULL;
    e = Name(id, Load, lineno, col_offset, c->c_arena);
    if (!e)
	return NULL;

    for (i = 2; i < NCH(n); i+=2) {
        id = NEW_IDENTIFIER(CHILD(n, i));
	if (!id)
	    return NULL;
	e = Attribute(e, id, Load, lineno, col_offset, c->c_arena);
	if (!e)
	    return NULL;
    }

    return e;
}

static expr_ty
ast_for_decorator(struct compiling *c, const node *n)
{
    /* decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE */
    expr_ty d = NULL;
    expr_ty name_expr;
    
    REQ(n, decorator);
    REQ(CHILD(n, 0), AT);
    REQ(RCHILD(n, -1), NEWLINE);
    
    name_expr = ast_for_dotted_name(c, CHILD(n, 1));
    if (!name_expr)
	return NULL;
	
    if (NCH(n) == 3) { /* No arguments */
	d = name_expr;
	name_expr = NULL;
    }
    else if (NCH(n) == 5) { /* Call with no arguments */
	d = Call(name_expr, NULL, NULL, NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
	if (!d)
	    return NULL;
	name_expr = NULL;
    }
    else {
	d = ast_for_call(c, CHILD(n, 3), name_expr);
	if (!d)
	    return NULL;
	name_expr = NULL;
    }

    return d;
}

static asdl_seq*
ast_for_decorators(struct compiling *c, const node *n)
{
    asdl_seq* decorator_seq;
    expr_ty d;
    int i;
    
    REQ(n, decorators);
    decorator_seq = asdl_seq_new(NCH(n), c->c_arena);
    if (!decorator_seq)
        return NULL;
	
    for (i = 0; i < NCH(n); i++) {
        d = ast_for_decorator(c, CHILD(n, i));
	    if (!d)
	        return NULL;
	    asdl_seq_SET(decorator_seq, i, d);
    }
    return decorator_seq;
}

static stmt_ty
ast_for_funcdef(struct compiling *c, const node *n)
{
    /* funcdef: 'def' [decorators] NAME parameters ':' suite */
    identifier name;
    arguments_ty args;
    asdl_seq *body;
    asdl_seq *decorator_seq = NULL;
    int name_i;

    REQ(n, funcdef);

    if (NCH(n) == 6) { /* decorators are present */
	decorator_seq = ast_for_decorators(c, CHILD(n, 0));
	if (!decorator_seq)
	    return NULL;
	name_i = 2;
    }
    else {
	name_i = 1;
    }

    name = NEW_IDENTIFIER(CHILD(n, name_i));
    if (!name)
	return NULL;
    else if (!strcmp(STR(CHILD(n, name_i)), "None")) {
	ast_error(CHILD(n, name_i), "assignment to None");
	return NULL;
    }
    args = ast_for_arguments(c, CHILD(n, name_i + 1));
    if (!args)
	return NULL;
    body = ast_for_suite(c, CHILD(n, name_i + 3));
    if (!body)
	return NULL;

    return FunctionDef(name, args, body, decorator_seq, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_lambdef(struct compiling *c, const node *n)
{
    /* lambdef: 'lambda' [varargslist] ':' test */
    arguments_ty args;
    expr_ty expression;

    if (NCH(n) == 3) {
        args = arguments(NULL, NULL, NULL, NULL, c->c_arena);
        if (!args)
            return NULL;
        expression = ast_for_expr(c, CHILD(n, 2));
        if (!expression)
            return NULL;
    }
    else {
        args = ast_for_arguments(c, CHILD(n, 1));
        if (!args)
            return NULL;
        expression = ast_for_expr(c, CHILD(n, 3));
        if (!expression)
            return NULL;
    }

    return Lambda(args, expression, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_ifexpr(struct compiling *c, const node *n)
{
    /* test: or_test 'if' or_test 'else' test */ 
    expr_ty expression, body, orelse;

    assert(NCH(n) == 5);
    body = ast_for_expr(c, CHILD(n, 0));
    if (!body)
    	return NULL;
    expression = ast_for_expr(c, CHILD(n, 2));
    if (!expression)
    	return NULL;
    orelse = ast_for_expr(c, CHILD(n, 4));
    if (!orelse)
	return NULL;
    return IfExp(expression, body, orelse, LINENO(n), n->n_col_offset, c->c_arena);
}

/* Count the number of 'for' loop in a list comprehension.

   Helper for ast_for_listcomp().
*/

static int
count_list_fors(const node *n)
{
    int n_fors = 0;
    node *ch = CHILD(n, 1);

 count_list_for:
    n_fors++;
    REQ(ch, list_for);
    if (NCH(ch) == 5)
	ch = CHILD(ch, 4);
    else
	return n_fors;
 count_list_iter:
    REQ(ch, list_iter);
    ch = CHILD(ch, 0);
    if (TYPE(ch) == list_for)
	goto count_list_for;
    else if (TYPE(ch) == list_if) {
        if (NCH(ch) == 3) {
            ch = CHILD(ch, 2);
            goto count_list_iter;
        }
        else
            return n_fors;
    }

    /* Should never be reached */
    PyErr_SetString(PyExc_SystemError, "logic error in count_list_fors");
    return -1;
}

/* Count the number of 'if' statements in a list comprehension.

   Helper for ast_for_listcomp().
*/

static int
count_list_ifs(const node *n)
{
    int n_ifs = 0;

 count_list_iter:
    REQ(n, list_iter);
    if (TYPE(CHILD(n, 0)) == list_for)
	return n_ifs;
    n = CHILD(n, 0);
    REQ(n, list_if);
    n_ifs++;
    if (NCH(n) == 2)
	return n_ifs;
    n = CHILD(n, 2);
    goto count_list_iter;
}

static expr_ty
ast_for_listcomp(struct compiling *c, const node *n)
{
    /* listmaker: test ( list_for | (',' test)* [','] )
       list_for: 'for' exprlist 'in' testlist_safe [list_iter]
       list_iter: list_for | list_if
       list_if: 'if' test [list_iter]
       testlist_safe: test [(',' test)+ [',']]
    */
    expr_ty elt;
    asdl_seq *listcomps;
    int i, n_fors;
    node *ch;

    REQ(n, listmaker);
    assert(NCH(n) > 1);

    elt = ast_for_expr(c, CHILD(n, 0));
    if (!elt)
        return NULL;

    n_fors = count_list_fors(n);
    if (n_fors == -1)
        return NULL;

    listcomps = asdl_seq_new(n_fors, c->c_arena);
    if (!listcomps)
    	return NULL;

    ch = CHILD(n, 1);
    for (i = 0; i < n_fors; i++) {
	comprehension_ty lc;
	asdl_seq *t;
        expr_ty expression;

	REQ(ch, list_for);

	t = ast_for_exprlist(c, CHILD(ch, 1), Store);
        if (!t)
            return NULL;
        expression = ast_for_testlist(c, CHILD(ch, 3));
        if (!expression)
            return NULL;

	if (asdl_seq_LEN(t) == 1)
	    lc = comprehension(asdl_seq_GET(t, 0), expression, NULL,
                               c->c_arena);
	else
	    lc = comprehension(Tuple(t, Store, LINENO(ch), ch->n_col_offset, c->c_arena),
                               expression, NULL, c->c_arena);
        if (!lc)
            return NULL;

	if (NCH(ch) == 5) {
	    int j, n_ifs;
	    asdl_seq *ifs;

	    ch = CHILD(ch, 4);
	    n_ifs = count_list_ifs(ch);
            if (n_ifs == -1)
                return NULL;

	    ifs = asdl_seq_new(n_ifs, c->c_arena);
	    if (!ifs)
		return NULL;

	    for (j = 0; j < n_ifs; j++) {
            REQ(ch, list_iter);
		    ch = CHILD(ch, 0);
		    REQ(ch, list_if);

    		asdl_seq_SET(ifs, j, ast_for_expr(c, CHILD(ch, 1)));
    		if (NCH(ch) == 3)
	    	    ch = CHILD(ch, 2);
	        }
	        /* on exit, must guarantee that ch is a list_for */
	        if (TYPE(ch) == list_iter)
		        ch = CHILD(ch, 0);
            lc->ifs = ifs;
	    }
	    asdl_seq_SET(listcomps, i, lc);
    }

    return ListComp(elt, listcomps, LINENO(n), n->n_col_offset, c->c_arena);
}

/*
   Count the number of 'for' loops in a generator expression.

   Helper for ast_for_genexp().
*/

static int
count_gen_fors(const node *n)
{
	int n_fors = 0;
	node *ch = CHILD(n, 1);

 count_gen_for:
	n_fors++;
	REQ(ch, gen_for);
	if (NCH(ch) == 5)
		ch = CHILD(ch, 4);
	else
		return n_fors;
 count_gen_iter:
	REQ(ch, gen_iter);
	ch = CHILD(ch, 0);
	if (TYPE(ch) == gen_for)
		goto count_gen_for;
	else if (TYPE(ch) == gen_if) {
		if (NCH(ch) == 3) {
			ch = CHILD(ch, 2);
			goto count_gen_iter;
		}
		else
		    return n_fors;
	}

	/* Should never be reached */
	PyErr_SetString(PyExc_SystemError,
			"logic error in count_gen_fors");
	return -1;
}

/* Count the number of 'if' statements in a generator expression.

   Helper for ast_for_genexp().
*/

static int
count_gen_ifs(const node *n)
{
	int n_ifs = 0;

	while (1) {
		REQ(n, gen_iter);
		if (TYPE(CHILD(n, 0)) == gen_for)
			return n_ifs;
		n = CHILD(n, 0);
		REQ(n, gen_if);
		n_ifs++;
		if (NCH(n) == 2)
			return n_ifs;
		n = CHILD(n, 2);
	}
}

/* TODO(jhylton): Combine with list comprehension code? */
static expr_ty
ast_for_genexp(struct compiling *c, const node *n)
{
    /* testlist_gexp: test ( gen_for | (',' test)* [','] )
       argument: [test '='] test [gen_for]	 # Really [keyword '='] test */
    expr_ty elt;
    asdl_seq *genexps;
    int i, n_fors;
    node *ch;
    
    assert(TYPE(n) == (testlist_gexp) || TYPE(n) == (argument));
    assert(NCH(n) > 1);
    
    elt = ast_for_expr(c, CHILD(n, 0));
    if (!elt)
        return NULL;
    
    n_fors = count_gen_fors(n);
    if (n_fors == -1)
        return NULL;

    genexps = asdl_seq_new(n_fors, c->c_arena);
    if (!genexps)
        return NULL;

    ch = CHILD(n, 1);
    for (i = 0; i < n_fors; i++) {
        comprehension_ty ge;
        asdl_seq *t;
        expr_ty expression;
        
        REQ(ch, gen_for);
        
        t = ast_for_exprlist(c, CHILD(ch, 1), Store);
        if (!t)
            return NULL;
        expression = ast_for_expr(c, CHILD(ch, 3));
        if (!expression)
            return NULL;

        if (asdl_seq_LEN(t) == 1)
            ge = comprehension(asdl_seq_GET(t, 0), expression,
                               NULL, c->c_arena);
        else
            ge = comprehension(Tuple(t, Store, LINENO(ch), ch->n_col_offset, c->c_arena),
                               expression, NULL, c->c_arena);

        if (!ge)
            return NULL;

        if (NCH(ch) == 5) {
            int j, n_ifs;
            asdl_seq *ifs;
            
            ch = CHILD(ch, 4);
            n_ifs = count_gen_ifs(ch);
            if (n_ifs == -1)
                return NULL;

            ifs = asdl_seq_new(n_ifs, c->c_arena);
            if (!ifs)
                return NULL;

            for (j = 0; j < n_ifs; j++) {
                REQ(ch, gen_iter);
                ch = CHILD(ch, 0);
                REQ(ch, gen_if);
                
                expression = ast_for_expr(c, CHILD(ch, 1));
                if (!expression)
                    return NULL;
                asdl_seq_SET(ifs, j, expression);
                if (NCH(ch) == 3)
                    ch = CHILD(ch, 2);
            }
            /* on exit, must guarantee that ch is a gen_for */
            if (TYPE(ch) == gen_iter)
                ch = CHILD(ch, 0);
            ge->ifs = ifs;
        }
        asdl_seq_SET(genexps, i, ge);
    }
    
    return GeneratorExp(elt, genexps, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_atom(struct compiling *c, const node *n)
{
    /* atom: '(' [yield_expr|testlist_gexp] ')' | '[' [listmaker] ']'
       | '{' [dictmaker] '}' | '`' testlist '`' | NAME | NUMBER | STRING+
    */
    node *ch = CHILD(n, 0);
    
    switch (TYPE(ch)) {
    case NAME:
	/* All names start in Load context, but may later be
	   changed. */
	return Name(NEW_IDENTIFIER(ch), Load, LINENO(n), n->n_col_offset, c->c_arena);
    case STRING: {
	PyObject *str = parsestrplus(c, n);
	if (!str)
	    return NULL;

	PyArena_AddPyObject(c->c_arena, str);
	return Str(str, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case NUMBER: {
	PyObject *pynum = parsenumber(STR(ch));
	if (!pynum)
	    return NULL;

	PyArena_AddPyObject(c->c_arena, pynum);
	return Num(pynum, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case LPAR: /* some parenthesized expressions */
	ch = CHILD(n, 1);
	
	if (TYPE(ch) == RPAR)
	    return Tuple(NULL, Load, LINENO(n), n->n_col_offset, c->c_arena);
	
	if (TYPE(ch) == yield_expr)
	    return ast_for_expr(c, ch);
	
	if ((NCH(ch) > 1) && (TYPE(CHILD(ch, 1)) == gen_for))
	    return ast_for_genexp(c, ch);
	
	return ast_for_testlist_gexp(c, ch);
    case LSQB: /* list (or list comprehension) */
	ch = CHILD(n, 1);
	
	if (TYPE(ch) == RSQB)
	    return List(NULL, Load, LINENO(n), n->n_col_offset, c->c_arena);
	
	REQ(ch, listmaker);
	if (NCH(ch) == 1 || TYPE(CHILD(ch, 1)) == COMMA) {
	    asdl_seq *elts = seq_for_testlist(c, ch);
	    if (!elts)
		return NULL;

	    return List(elts, Load, LINENO(n), n->n_col_offset, c->c_arena);
	}
	else
	    return ast_for_listcomp(c, ch);
    case LBRACE: {
	/* dictmaker: test ':' test (',' test ':' test)* [','] */
	int i, size;
	asdl_seq *keys, *values;
	
	ch = CHILD(n, 1);
	size = (NCH(ch) + 1) / 4; /* +1 in case no trailing comma */
	keys = asdl_seq_new(size, c->c_arena);
	if (!keys)
	    return NULL;
	
	values = asdl_seq_new(size, c->c_arena);
	if (!values)
	    return NULL;
	
	for (i = 0; i < NCH(ch); i += 4) {
	    expr_ty expression;
	    
	    expression = ast_for_expr(c, CHILD(ch, i));
	    if (!expression)
		return NULL;

	    asdl_seq_SET(keys, i / 4, expression);

	    expression = ast_for_expr(c, CHILD(ch, i + 2));
	    if (!expression)
		return NULL;

	    asdl_seq_SET(values, i / 4, expression);
	}
	return Dict(keys, values, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case BACKQUOTE: { /* repr */
	expr_ty expression = ast_for_testlist(c, CHILD(n, 1));
	if (!expression)
	    return NULL;

	return Repr(expression, LINENO(n), n->n_col_offset, c->c_arena);
    }
    default:
	PyErr_Format(PyExc_SystemError, "unhandled atom %d", TYPE(ch));
	return NULL;
    }
}

static slice_ty
ast_for_slice(struct compiling *c, const node *n)
{
    node *ch;
    expr_ty lower = NULL, upper = NULL, step = NULL;

    REQ(n, subscript);

    /*
       subscript: '.' '.' '.' | test | [test] ':' [test] [sliceop]
       sliceop: ':' [test]
    */
    ch = CHILD(n, 0);
    if (TYPE(ch) == DOT)
	return Ellipsis(c->c_arena);

    if (NCH(n) == 1 && TYPE(ch) == test) {
        /* 'step' variable hold no significance in terms of being used over
           other vars */
        step = ast_for_expr(c, ch); 
        if (!step)
            return NULL;
            
	return Index(step, c->c_arena);
    }

    if (TYPE(ch) == test) {
	lower = ast_for_expr(c, ch);
        if (!lower)
            return NULL;
    }

    /* If there's an upper bound it's in the second or third position. */
    if (TYPE(ch) == COLON) {
	if (NCH(n) > 1) {
	    node *n2 = CHILD(n, 1);

	    if (TYPE(n2) == test) {
		upper = ast_for_expr(c, n2);
                if (!upper)
                    return NULL;
            }
	}
    } else if (NCH(n) > 2) {
	node *n2 = CHILD(n, 2);

	if (TYPE(n2) == test) {
	    upper = ast_for_expr(c, n2);
            if (!upper)
                return NULL;
        }
    }

    ch = CHILD(n, NCH(n) - 1);
    if (TYPE(ch) == sliceop) {
	if (NCH(ch) == 1)
            /* XXX: If only 1 child, then should just be a colon.  Should we
               just skip assigning and just get to the return? */
	    ch = CHILD(ch, 0);
	else
	    ch = CHILD(ch, 1);
	if (TYPE(ch) == test) {
	    step = ast_for_expr(c, ch);
            if (!step)
                return NULL;
        }
    }

    return Slice(lower, upper, step, c->c_arena);
}

static expr_ty
ast_for_binop(struct compiling *c, const node *n)
{
	/* Must account for a sequence of expressions.
	   How should A op B op C by represented?  
	   BinOp(BinOp(A, op, B), op, C).
	*/

	int i, nops;
	expr_ty expr1, expr2, result;
        operator_ty operator;

        expr1 = ast_for_expr(c, CHILD(n, 0));
        if (!expr1)
            return NULL;

        expr2 = ast_for_expr(c, CHILD(n, 2));
        if (!expr2)
            return NULL;

        operator = get_operator(CHILD(n, 1));
        if (!operator)
            return NULL;

	result = BinOp(expr1, operator, expr2, LINENO(n), n->n_col_offset, c->c_arena);
	if (!result)
            return NULL;

	nops = (NCH(n) - 1) / 2;
	for (i = 1; i < nops; i++) {
		expr_ty tmp_result, tmp;
		const node* next_oper = CHILD(n, i * 2 + 1);

		operator = get_operator(next_oper);
                if (!operator)
                    return NULL;

                tmp = ast_for_expr(c, CHILD(n, i * 2 + 2));
                if (!tmp)
                    return NULL;

                tmp_result = BinOp(result, operator, tmp, 
				   LINENO(next_oper), next_oper->n_col_offset, c->c_arena);
		if (!tmp) 
			return NULL;
		result = tmp_result;
	}
	return result;
}

static expr_ty
ast_for_trailer(struct compiling *c, const node *n, expr_ty left_expr)
{
    /* trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME 
       subscriptlist: subscript (',' subscript)* [',']
       subscript: '.' '.' '.' | test | [test] ':' [test] [sliceop]
     */
    REQ(n, trailer);
    if (TYPE(CHILD(n, 0)) == LPAR) {
        if (NCH(n) == 2)
            return Call(left_expr, NULL, NULL, NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
        else
            return ast_for_call(c, CHILD(n, 1), left_expr);
    }
    else if (TYPE(CHILD(n, 0)) == DOT ) {
        return Attribute(left_expr, NEW_IDENTIFIER(CHILD(n, 1)), Load,
                         LINENO(n), n->n_col_offset, c->c_arena);
    }
    else {
        REQ(CHILD(n, 0), LSQB);
        REQ(CHILD(n, 2), RSQB);
        n = CHILD(n, 1);
        if (NCH(n) == 1) {
            slice_ty slc = ast_for_slice(c, CHILD(n, 0));
            if (!slc)
                return NULL;
            return Subscript(left_expr, slc, Load, LINENO(n), n->n_col_offset, c->c_arena);
        }
        else {
            /* The grammar is ambiguous here. The ambiguity is resolved 
               by treating the sequence as a tuple literal if there are
               no slice features.
            */
            int j;
            slice_ty slc;
            expr_ty e;
            bool simple = true;
            asdl_seq *slices, *elts;
            slices = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
            if (!slices)
                return NULL;
            for (j = 0; j < NCH(n); j += 2) {
                slc = ast_for_slice(c, CHILD(n, j));
                if (!slc)
                    return NULL;
                if (slc->kind != Index_kind)
                    simple = false;
                asdl_seq_SET(slices, j / 2, slc);
            }
            if (!simple) {
                return Subscript(left_expr, ExtSlice(slices, c->c_arena),
                                 Load, LINENO(n), n->n_col_offset, c->c_arena);
            }
            /* extract Index values and put them in a Tuple */
            elts = asdl_seq_new(asdl_seq_LEN(slices), c->c_arena);
            if (!elts)
                return NULL;
            for (j = 0; j < asdl_seq_LEN(slices); ++j) {
                slc = (slice_ty)asdl_seq_GET(slices, j);
                assert(slc->kind == Index_kind  && slc->v.Index.value);
                asdl_seq_SET(elts, j, slc->v.Index.value);
            }
            e = Tuple(elts, Load, LINENO(n), n->n_col_offset, c->c_arena);
            if (!e)
                return NULL;
            return Subscript(left_expr, Index(e, c->c_arena),
                             Load, LINENO(n), n->n_col_offset, c->c_arena);
        }
    }
}

static expr_ty
ast_for_power(struct compiling *c, const node *n)
{
    /* power: atom trailer* ('**' factor)*
     */
    int i;
    expr_ty e, tmp;
    REQ(n, power);
    e = ast_for_atom(c, CHILD(n, 0));
    if (!e)
        return NULL;
    if (NCH(n) == 1)
        return e;
    for (i = 1; i < NCH(n); i++) {
        node *ch = CHILD(n, i);
        if (TYPE(ch) != trailer)
            break;
        tmp = ast_for_trailer(c, ch, e);
        if (!tmp)
            return NULL;
	tmp->lineno = e->lineno;
	tmp->col_offset = e->col_offset;
        e = tmp;
    }
    if (TYPE(CHILD(n, NCH(n) - 1)) == factor) {
        expr_ty f = ast_for_expr(c, CHILD(n, NCH(n) - 1));
        if (!f)
            return NULL;
        tmp = BinOp(e, Pow, f, LINENO(n), n->n_col_offset, c->c_arena);
        if (!tmp)
            return NULL;
        e = tmp;
    }
    return e;
}

/* Do not name a variable 'expr'!  Will cause a compile error.
*/

static expr_ty
ast_for_expr(struct compiling *c, const node *n)
{
    /* handle the full range of simple expressions
       test: or_test ['if' or_test 'else' test] | lambdef
       or_test: and_test ('or' and_test)* 
       and_test: not_test ('and' not_test)*
       not_test: 'not' not_test | comparison
       comparison: expr (comp_op expr)*
       expr: xor_expr ('|' xor_expr)*
       xor_expr: and_expr ('^' and_expr)*
       and_expr: shift_expr ('&' shift_expr)*
       shift_expr: arith_expr (('<<'|'>>') arith_expr)*
       arith_expr: term (('+'|'-') term)*
       term: factor (('*'|'/'|'%'|'//') factor)*
       factor: ('+'|'-'|'~') factor | power
       power: atom trailer* ('**' factor)*

       As well as modified versions that exist for backward compatibility,
       to explicitly allow:
       [ x for x in lambda: 0, lambda: 1 ]
       (which would be ambiguous without these extra rules)
       
       old_test: or_test | old_lambdef
       old_lambdef: 'lambda' [vararglist] ':' old_test

    */

    asdl_seq *seq;
    int i;

 loop:
    switch (TYPE(n)) {
        case test:
        case old_test:
            if (TYPE(CHILD(n, 0)) == lambdef ||
                TYPE(CHILD(n, 0)) == old_lambdef)
                return ast_for_lambdef(c, CHILD(n, 0));
            else if (NCH(n) > 1)
                return ast_for_ifexpr(c, n);
	    /* Fallthrough */
	case or_test:
        case and_test:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            seq = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
            if (!seq)
                return NULL;
            for (i = 0; i < NCH(n); i += 2) {
                expr_ty e = ast_for_expr(c, CHILD(n, i));
                if (!e)
                    return NULL;
                asdl_seq_SET(seq, i / 2, e);
            }
            if (!strcmp(STR(CHILD(n, 1)), "and"))
                return BoolOp(And, seq, LINENO(n), n->n_col_offset, c->c_arena);
            assert(!strcmp(STR(CHILD(n, 1)), "or"));
            return BoolOp(Or, seq, LINENO(n), n->n_col_offset, c->c_arena);
        case not_test:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                expr_ty expression = ast_for_expr(c, CHILD(n, 1));
                if (!expression)
                    return NULL;

                return UnaryOp(Not, expression, LINENO(n), n->n_col_offset, c->c_arena);
            }
        case comparison:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                expr_ty expression;
                asdl_seq *ops, *cmps;
                ops = asdl_seq_new(NCH(n) / 2, c->c_arena);
                if (!ops)
                    return NULL;
                cmps = asdl_seq_new(NCH(n) / 2, c->c_arena);
                if (!cmps) {
                    return NULL;
                }
                for (i = 1; i < NCH(n); i += 2) {
                    /* XXX cmpop_ty is just an enum */
                    cmpop_ty operator;

                    operator = ast_for_comp_op(CHILD(n, i));
                    if (!operator) {
                        return NULL;
		    }

                    expression = ast_for_expr(c, CHILD(n, i + 1));
                    if (!expression) {
                        return NULL;
		    }
                        
                    asdl_seq_SET(ops, i / 2, (void *)(Py_uintptr_t)operator);
                    asdl_seq_SET(cmps, i / 2, expression);
                }
                expression = ast_for_expr(c, CHILD(n, 0));
                if (!expression) {
                    return NULL;
		}
                    
                return Compare(expression, ops, cmps, LINENO(n), n->n_col_offset, c->c_arena);
            }
            break;

        /* The next five cases all handle BinOps.  The main body of code
           is the same in each case, but the switch turned inside out to
           reuse the code for each type of operator.
         */
        case expr:
        case xor_expr:
        case and_expr:
        case shift_expr:
        case arith_expr:
        case term:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            return ast_for_binop(c, n);
        case yield_expr: {
	    expr_ty exp = NULL;
	    if (NCH(n) == 2) {
		exp = ast_for_testlist(c, CHILD(n, 1));
		if (!exp)
		    return NULL;
	    }
	    return Yield(exp, LINENO(n), n->n_col_offset, c->c_arena);
	}
        case factor: {
            expr_ty expression;
            
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }

            expression = ast_for_expr(c, CHILD(n, 1));
            if (!expression)
                return NULL;

            switch (TYPE(CHILD(n, 0))) {
                case PLUS:
                    return UnaryOp(UAdd, expression, LINENO(n), n->n_col_offset, c->c_arena);
                case MINUS:
                    return UnaryOp(USub, expression, LINENO(n), n->n_col_offset, c->c_arena);
                case TILDE:
                    return UnaryOp(Invert, expression, LINENO(n), n->n_col_offset, c->c_arena);
            }
            PyErr_Format(PyExc_SystemError, "unhandled factor: %d",
	    		 TYPE(CHILD(n, 0)));
            break;
        }
        case power:
            return ast_for_power(c, n);
        default:
            PyErr_Format(PyExc_SystemError, "unhandled expr: %d", TYPE(n));
            return NULL;
    }
    /* should never get here unless if error is set */
    return NULL;
}

static expr_ty
ast_for_call(struct compiling *c, const node *n, expr_ty func)
{
    /*
      arglist: (argument ',')* (argument [',']| '*' test [',' '**' test]
               | '**' test)
      argument: [test '='] test [gen_for]	 # Really [keyword '='] test
    */

    int i, nargs, nkeywords, ngens;
    asdl_seq *args;
    asdl_seq *keywords;
    expr_ty vararg = NULL, kwarg = NULL;

    REQ(n, arglist);

    nargs = 0;
    nkeywords = 0;
    ngens = 0;
    for (i = 0; i < NCH(n); i++) {
	node *ch = CHILD(n, i);
	if (TYPE(ch) == argument) {
	    if (NCH(ch) == 1)
		nargs++;
	    else if (TYPE(CHILD(ch, 1)) == gen_for)
		ngens++;
            else
		nkeywords++;
	}
    }
    if (ngens > 1 || (ngens && (nargs || nkeywords))) {
        ast_error(n, "Generator expression must be parenthesized "
		  "if not sole argument");
	return NULL;
    }

    if (nargs + nkeywords + ngens > 255) {
      ast_error(n, "more than 255 arguments");
      return NULL;
    }

    args = asdl_seq_new(nargs + ngens, c->c_arena);
    if (!args)
        return NULL;
    keywords = asdl_seq_new(nkeywords, c->c_arena);
    if (!keywords)
        return NULL;
    nargs = 0;
    nkeywords = 0;
    for (i = 0; i < NCH(n); i++) {
	node *ch = CHILD(n, i);
	if (TYPE(ch) == argument) {
	    expr_ty e;
	    if (NCH(ch) == 1) {
		e = ast_for_expr(c, CHILD(ch, 0));
                if (!e)
                    return NULL;
		asdl_seq_SET(args, nargs++, e);
	    }  
	    else if (TYPE(CHILD(ch, 1)) == gen_for) {
        	e = ast_for_genexp(c, ch);
                if (!e)
                    return NULL;
		asdl_seq_SET(args, nargs++, e);
            }
	    else {
		keyword_ty kw;
		identifier key;

		/* CHILD(ch, 0) is test, but must be an identifier? */ 
		e = ast_for_expr(c, CHILD(ch, 0));
                if (!e)
                    return NULL;
                /* f(lambda x: x[0] = 3) ends up getting parsed with
                 * LHS test = lambda x: x[0], and RHS test = 3.
                 * SF bug 132313 points out that complaining about a keyword
                 * then is very confusing.
                 */
                if (e->kind == Lambda_kind) {
                  ast_error(CHILD(ch, 0), "lambda cannot contain assignment");
                  return NULL;
                } else if (e->kind != Name_kind) {
                  ast_error(CHILD(ch, 0), "keyword can't be an expression");
                  return NULL;
                }
		key = e->v.Name.id;
		e = ast_for_expr(c, CHILD(ch, 2));
                if (!e)
                    return NULL;
		kw = keyword(key, e, c->c_arena);
                if (!kw)
                    return NULL;
		asdl_seq_SET(keywords, nkeywords++, kw);
	    }
	}
	else if (TYPE(ch) == STAR) {
	    vararg = ast_for_expr(c, CHILD(n, i+1));
	    i++;
	}
	else if (TYPE(ch) == DOUBLESTAR) {
	    kwarg = ast_for_expr(c, CHILD(n, i+1));
	    i++;
	}
    }

    return Call(func, args, keywords, vararg, kwarg, func->lineno, func->col_offset, c->c_arena);
}

static expr_ty
ast_for_testlist(struct compiling *c, const node* n)
{
    /* testlist_gexp: test (',' test)* [','] */
    /* testlist: test (',' test)* [','] */
    /* testlist_safe: test (',' test)+ [','] */
    /* testlist1: test (',' test)* */
    assert(NCH(n) > 0);
    if (TYPE(n) == testlist_gexp) {
        if (NCH(n) > 1)
            assert(TYPE(CHILD(n, 1)) != gen_for);
    }
    else {
        assert(TYPE(n) == testlist ||
               TYPE(n) == testlist_safe ||
               TYPE(n) == testlist1);
    }
    if (NCH(n) == 1)
	return ast_for_expr(c, CHILD(n, 0));
    else {
        asdl_seq *tmp = seq_for_testlist(c, n);
        if (!tmp)
            return NULL;
	return Tuple(tmp, Load, LINENO(n), n->n_col_offset, c->c_arena);
    }
}

static expr_ty
ast_for_testlist_gexp(struct compiling *c, const node* n)
{
    /* testlist_gexp: test ( gen_for | (',' test)* [','] ) */
    /* argument: test [ gen_for ] */
    assert(TYPE(n) == testlist_gexp || TYPE(n) == argument);
    if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == gen_for)
	return ast_for_genexp(c, n);
    return ast_for_testlist(c, n);
}

/* like ast_for_testlist() but returns a sequence */
static asdl_seq*
ast_for_class_bases(struct compiling *c, const node* n)
{
    /* testlist: test (',' test)* [','] */
    assert(NCH(n) > 0);
    REQ(n, testlist);
    if (NCH(n) == 1) {
        expr_ty base;
        asdl_seq *bases = asdl_seq_new(1, c->c_arena);
        if (!bases)
            return NULL;
        base = ast_for_expr(c, CHILD(n, 0));
        if (!base)
            return NULL;
        asdl_seq_SET(bases, 0, base);
        return bases;
    }

    return seq_for_testlist(c, n);
}

static stmt_ty
ast_for_expr_stmt(struct compiling *c, const node *n)
{
    REQ(n, expr_stmt);
    /* expr_stmt: testlist (augassign (yield_expr|testlist) 
                | ('=' (yield_expr|testlist))*)
       testlist: test (',' test)* [',']
       augassign: '+=' | '-=' | '*=' | '/=' | '%=' | '&=' | '|=' | '^='
	        | '<<=' | '>>=' | '**=' | '//='
       test: ... here starts the operator precendence dance
     */

    if (NCH(n) == 1) {
	expr_ty e = ast_for_testlist(c, CHILD(n, 0));
        if (!e)
            return NULL;

	return Expr(e, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (TYPE(CHILD(n, 1)) == augassign) {
        expr_ty expr1, expr2;
        operator_ty operator;
	node *ch = CHILD(n, 0);

	if (TYPE(ch) == testlist)
	    expr1 = ast_for_testlist(c, ch);
	else
	    expr1 = Yield(ast_for_expr(c, CHILD(ch, 0)), LINENO(ch), n->n_col_offset,
                          c->c_arena);

        if (!expr1)
            return NULL;
        /* TODO(jhylton): Figure out why set_context() can't be used here. */
        switch (expr1->kind) {
            case GeneratorExp_kind:
                ast_error(ch, "augmented assignment to generator "
                          "expression not possible");
                return NULL;
            case Name_kind: {
                const char *var_name = PyString_AS_STRING(expr1->v.Name.id);
                if (var_name[0] == 'N' && !strcmp(var_name, "None")) {
                    ast_error(ch, "assignment to None");
                    return NULL;
                }
                break;
            }
            case Attribute_kind:
            case Subscript_kind:
                break;
            default:
                ast_error(ch, "illegal expression for augmented "
                          "assignment");
                return NULL;
        }

	ch = CHILD(n, 2);
	if (TYPE(ch) == testlist)
	    expr2 = ast_for_testlist(c, ch);
	else
	    expr2 = Yield(ast_for_expr(c, ch), LINENO(ch), ch->n_col_offset, c->c_arena);
        if (!expr2)
            return NULL;

        operator = ast_for_augassign(CHILD(n, 1));
        if (!operator)
            return NULL;

	return AugAssign(expr1, operator, expr2, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else {
	int i;
	asdl_seq *targets;
	node *value;
        expr_ty expression;

	/* a normal assignment */
	REQ(CHILD(n, 1), EQUAL);
	targets = asdl_seq_new(NCH(n) / 2, c->c_arena);
	if (!targets)
	    return NULL;
	for (i = 0; i < NCH(n) - 2; i += 2) {
	    expr_ty e;
	    node *ch = CHILD(n, i);
	    if (TYPE(ch) == yield_expr) {
		ast_error(ch, "assignment to yield expression not possible");
		return NULL;
	    }
	    e = ast_for_testlist(c, ch);

	    /* set context to assign */
	    if (!e) 
	      return NULL;

	    if (!set_context(e, Store, CHILD(n, i)))
	      return NULL;

	    asdl_seq_SET(targets, i / 2, e);
	}
	value = CHILD(n, NCH(n) - 1);
	if (TYPE(value) == testlist)
	    expression = ast_for_testlist(c, value);
	else
	    expression = ast_for_expr(c, value);
	if (!expression)
	    return NULL;
	return Assign(targets, expression, LINENO(n), n->n_col_offset, c->c_arena);
    }
}

static stmt_ty
ast_for_print_stmt(struct compiling *c, const node *n)
{
    /* print_stmt: 'print' ( [ test (',' test)* [','] ]
                             | '>>' test [ (',' test)+ [','] ] )
     */
    expr_ty dest = NULL, expression;
    asdl_seq *seq;
    bool nl;
    int i, j, start = 1;

    REQ(n, print_stmt);
    if (NCH(n) >= 2 && TYPE(CHILD(n, 1)) == RIGHTSHIFT) {
	dest = ast_for_expr(c, CHILD(n, 2));
        if (!dest)
            return NULL;
	    start = 4;
    }
    seq = asdl_seq_new((NCH(n) + 1 - start) / 2, c->c_arena);
    if (!seq)
    	return NULL;
    for (i = start, j = 0; i < NCH(n); i += 2, ++j) {
        expression = ast_for_expr(c, CHILD(n, i));
        if (!expression)
            return NULL;
    	asdl_seq_SET(seq, j, expression);
    }
    nl = (TYPE(CHILD(n, NCH(n) - 1)) == COMMA) ? false : true;
    return Print(dest, seq, nl, LINENO(n), n->n_col_offset, c->c_arena);
}

static asdl_seq *
ast_for_exprlist(struct compiling *c, const node *n, int context)
{
    asdl_seq *seq;
    int i;
    expr_ty e;

    REQ(n, exprlist);

    seq = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
    if (!seq)
	return NULL;
    for (i = 0; i < NCH(n); i += 2) {
	e = ast_for_expr(c, CHILD(n, i));
	if (!e)
	    return NULL;
	asdl_seq_SET(seq, i / 2, e);
	if (context && !set_context(e, context, CHILD(n, i)))
	    return NULL;
    }
    return seq;
}

static stmt_ty
ast_for_del_stmt(struct compiling *c, const node *n)
{
    asdl_seq *expr_list;
    
    /* del_stmt: 'del' exprlist */
    REQ(n, del_stmt);

    expr_list = ast_for_exprlist(c, CHILD(n, 1), Del);
    if (!expr_list)
        return NULL;
    return Delete(expr_list, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_flow_stmt(struct compiling *c, const node *n)
{
    /*
      flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt
                 | yield_stmt
      break_stmt: 'break'
      continue_stmt: 'continue'
      return_stmt: 'return' [testlist]
      yield_stmt: yield_expr
      yield_expr: 'yield' testlist
      raise_stmt: 'raise' [test [',' test [',' test]]]
    */
    node *ch;

    REQ(n, flow_stmt);
    ch = CHILD(n, 0);
    switch (TYPE(ch)) {
        case break_stmt:
            return Break(LINENO(n), n->n_col_offset, c->c_arena);
        case continue_stmt:
            return Continue(LINENO(n), n->n_col_offset, c->c_arena);
        case yield_stmt: { /* will reduce to yield_expr */
	    expr_ty exp = ast_for_expr(c, CHILD(ch, 0));
	    if (!exp)
		return NULL;
            return Expr(exp, LINENO(n), n->n_col_offset, c->c_arena);
        }
        case return_stmt:
            if (NCH(ch) == 1)
                return Return(NULL, LINENO(n), n->n_col_offset, c->c_arena);
            else {
                expr_ty expression = ast_for_testlist(c, CHILD(ch, 1));
                if (!expression)
                    return NULL;
                return Return(expression, LINENO(n), n->n_col_offset, c->c_arena);
            }
        case raise_stmt:
            if (NCH(ch) == 1)
                return Raise(NULL, NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
            else if (NCH(ch) == 2) {
                expr_ty expression = ast_for_expr(c, CHILD(ch, 1));
                if (!expression)
                    return NULL;
                return Raise(expression, NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
            }
            else if (NCH(ch) == 4) {
                expr_ty expr1, expr2;

                expr1 = ast_for_expr(c, CHILD(ch, 1));
                if (!expr1)
                    return NULL;
                expr2 = ast_for_expr(c, CHILD(ch, 3));
                if (!expr2)
                    return NULL;

                return Raise(expr1, expr2, NULL, LINENO(n), n->n_col_offset, c->c_arena);
            }
            else if (NCH(ch) == 6) {
                expr_ty expr1, expr2, expr3;

                expr1 = ast_for_expr(c, CHILD(ch, 1));
                if (!expr1)
                    return NULL;
                expr2 = ast_for_expr(c, CHILD(ch, 3));
                if (!expr2)
                    return NULL;
                expr3 = ast_for_expr(c, CHILD(ch, 5));
                if (!expr3)
                    return NULL;
                    
                return Raise(expr1, expr2, expr3, LINENO(n), n->n_col_offset, c->c_arena);
            }
        default:
            PyErr_Format(PyExc_SystemError,
                         "unexpected flow_stmt: %d", TYPE(ch));
            return NULL;
    }

    PyErr_SetString(PyExc_SystemError, "unhandled flow statement");
    return NULL;
}

static alias_ty
alias_for_import_name(struct compiling *c, const node *n)
{
    /*
      import_as_name: NAME ['as' NAME]
      dotted_as_name: dotted_name ['as' NAME]
      dotted_name: NAME ('.' NAME)*
    */
    PyObject *str;

 loop:
    switch (TYPE(n)) {
        case import_as_name:
            str = (NCH(n) == 3) ? NEW_IDENTIFIER(CHILD(n, 2)) : NULL;
            return alias(NEW_IDENTIFIER(CHILD(n, 0)), str, c->c_arena);
        case dotted_as_name:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                alias_ty a = alias_for_import_name(c, CHILD(n, 0));
                assert(!a->asname);
                a->asname = NEW_IDENTIFIER(CHILD(n, 2));
                return a;
            }
            break;
        case dotted_name:
            if (NCH(n) == 1)
                return alias(NEW_IDENTIFIER(CHILD(n, 0)), NULL, c->c_arena);
            else {
                /* Create a string of the form "a.b.c" */
                int i;
                size_t len;
                char *s;

                len = 0;
                for (i = 0; i < NCH(n); i += 2)
                    /* length of string plus one for the dot */
                    len += strlen(STR(CHILD(n, i))) + 1;
                len--; /* the last name doesn't have a dot */
                str = PyString_FromStringAndSize(NULL, len);
                if (!str)
                    return NULL;
                s = PyString_AS_STRING(str);
                if (!s)
                    return NULL;
                for (i = 0; i < NCH(n); i += 2) {
                    char *sch = STR(CHILD(n, i));
                    strcpy(s, STR(CHILD(n, i)));
                    s += strlen(sch);
                    *s++ = '.';
                }
                --s;
                *s = '\0';
                PyString_InternInPlace(&str);
		PyArena_AddPyObject(c->c_arena, str);
                return alias(str, NULL, c->c_arena);
            }
            break;
        case STAR:
	    str = PyString_InternFromString("*");
	    PyArena_AddPyObject(c->c_arena, str);
            return alias(str, NULL, c->c_arena);
        default:
            PyErr_Format(PyExc_SystemError,
                         "unexpected import name: %d", TYPE(n));
            return NULL;
    }

    PyErr_SetString(PyExc_SystemError, "unhandled import name condition");
    return NULL;
}

static stmt_ty
ast_for_import_stmt(struct compiling *c, const node *n)
{
    /*
      import_stmt: import_name | import_from
      import_name: 'import' dotted_as_names
      import_from: 'from' ('.'* dotted_name | '.') 'import'
                          ('*' | '(' import_as_names ')' | import_as_names)
    */
    int lineno;
    int col_offset;
    int i;
    asdl_seq *aliases;

    REQ(n, import_stmt);
    lineno = LINENO(n);
    col_offset = n->n_col_offset;
    n = CHILD(n, 0);
    if (TYPE(n) == import_name) {
        n = CHILD(n, 1);
	REQ(n, dotted_as_names);
	aliases = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
	if (!aliases)
		return NULL;
	for (i = 0; i < NCH(n); i += 2) {
            alias_ty import_alias = alias_for_import_name(c, CHILD(n, i));
            if (!import_alias)
                return NULL;
	    asdl_seq_SET(aliases, i / 2, import_alias);
        }
	return Import(aliases, lineno, col_offset, c->c_arena);
    }
    else if (TYPE(n) == import_from) {
        int n_children;
	int idx, ndots = 0;
	alias_ty mod = NULL;
	identifier modname;
	
       /* Count the number of dots (for relative imports) and check for the
          optional module name */
	for (idx = 1; idx < NCH(n); idx++) {
	    if (TYPE(CHILD(n, idx)) == dotted_name) {
	    	mod = alias_for_import_name(c, CHILD(n, idx));
	    	idx++;
	    	break;
	    } else if (TYPE(CHILD(n, idx)) != DOT) {
	        break;
	    }
	    ndots++;
	}
	idx++; /* skip over the 'import' keyword */
        switch (TYPE(CHILD(n, idx))) {
        case STAR:
            /* from ... import * */
	    n = CHILD(n, idx);
	    n_children = 1;
	    if (ndots) {
	        ast_error(n, "'import *' not allowed with 'from .'");
	        return NULL;
	    }
	    break;
	case LPAR:
	    /* from ... import (x, y, z) */
	    n = CHILD(n, idx + 1);
	    n_children = NCH(n);
	    break;
	case import_as_names:
	    /* from ... import x, y, z */
	    n = CHILD(n, idx);
	    n_children = NCH(n);
            if (n_children % 2 == 0) {
                ast_error(n, "trailing comma not allowed without"
                             " surrounding parentheses");
                return NULL;
            }
	    break;
	default:
	    ast_error(n, "Unexpected node-type in from-import");
	    return NULL;
	}

	aliases = asdl_seq_new((n_children + 1) / 2, c->c_arena);
	if (!aliases)
            return NULL;

        /* handle "from ... import *" special b/c there's no children */
        if (TYPE(n) == STAR) {
            alias_ty import_alias = alias_for_import_name(c, n);
            if (!import_alias)
                return NULL;
	        asdl_seq_SET(aliases, 0, import_alias);
        }
        else {
    	    for (i = 0; i < NCH(n); i += 2) {
                alias_ty import_alias = alias_for_import_name(c, CHILD(n, i));
                if (!import_alias)
                    return NULL;
	            asdl_seq_SET(aliases, i / 2, import_alias);
            }
        }
        if (mod != NULL)
            modname = mod->name;
        else
            modname = new_identifier("", c->c_arena);
        return ImportFrom(modname, aliases, ndots, lineno, col_offset,
                          c->c_arena);
    }
    PyErr_Format(PyExc_SystemError,
                 "unknown import statement: starts with command '%s'",
                 STR(CHILD(n, 0)));
    return NULL;
}

static stmt_ty
ast_for_global_stmt(struct compiling *c, const node *n)
{
    /* global_stmt: 'global' NAME (',' NAME)* */
    identifier name;
    asdl_seq *s;
    int i;

    REQ(n, global_stmt);
    s = asdl_seq_new(NCH(n) / 2, c->c_arena);
    if (!s)
    	return NULL;
    for (i = 1; i < NCH(n); i += 2) {
	name = NEW_IDENTIFIER(CHILD(n, i));
	if (!name)
	    return NULL;
	asdl_seq_SET(s, i / 2, name);
    }
    return Global(s, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_exec_stmt(struct compiling *c, const node *n)
{
    expr_ty expr1, globals = NULL, locals = NULL;
    int n_children = NCH(n);
    if (n_children != 2 && n_children != 4 && n_children != 6) {
        PyErr_Format(PyExc_SystemError,
                     "poorly formed 'exec' statement: %d parts to statement",
                     n_children);
        return NULL;
    }

    /* exec_stmt: 'exec' expr ['in' test [',' test]] */
    REQ(n, exec_stmt);
    expr1 = ast_for_expr(c, CHILD(n, 1));
    if (!expr1)
        return NULL;
    if (n_children >= 4) {
        globals = ast_for_expr(c, CHILD(n, 3));
        if (!globals)
            return NULL;
    }
    if (n_children == 6) {
        locals = ast_for_expr(c, CHILD(n, 5));
        if (!locals)
            return NULL;
    }

    return Exec(expr1, globals, locals, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_assert_stmt(struct compiling *c, const node *n)
{
    /* assert_stmt: 'assert' test [',' test] */
    REQ(n, assert_stmt);
    if (NCH(n) == 2) {
        expr_ty expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
	return Assert(expression, NULL, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (NCH(n) == 4) {
        expr_ty expr1, expr2;

        expr1 = ast_for_expr(c, CHILD(n, 1));
        if (!expr1)
            return NULL;
        expr2 = ast_for_expr(c, CHILD(n, 3));
        if (!expr2)
            return NULL;
            
	return Assert(expr1, expr2, LINENO(n), n->n_col_offset, c->c_arena);
    }
    PyErr_Format(PyExc_SystemError,
                 "improper number of parts to 'assert' statement: %d",
                 NCH(n));
    return NULL;
}

static asdl_seq *
ast_for_suite(struct compiling *c, const node *n)
{
    /* suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT */
    asdl_seq *seq;
    stmt_ty s;
    int i, total, num, end, pos = 0;
    node *ch;

    REQ(n, suite);

    total = num_stmts(n);
    seq = asdl_seq_new(total, c->c_arena);
    if (!seq)
    	return NULL;
    if (TYPE(CHILD(n, 0)) == simple_stmt) {
	n = CHILD(n, 0);
	/* simple_stmt always ends with a NEWLINE,
	   and may have a trailing SEMI 
	*/
	end = NCH(n) - 1;
	if (TYPE(CHILD(n, end - 1)) == SEMI)
	    end--;
        /* loop by 2 to skip semi-colons */
	for (i = 0; i < end; i += 2) {
	    ch = CHILD(n, i);
	    s = ast_for_stmt(c, ch);
	    if (!s)
		return NULL;
	    asdl_seq_SET(seq, pos++, s);
	}
    }
    else {
	for (i = 2; i < (NCH(n) - 1); i++) {
	    ch = CHILD(n, i);
	    REQ(ch, stmt);
	    num = num_stmts(ch);
	    if (num == 1) {
		/* small_stmt or compound_stmt with only one child */
		s = ast_for_stmt(c, ch);
		if (!s)
		    return NULL;
		asdl_seq_SET(seq, pos++, s);
	    }
	    else {
		int j;
		ch = CHILD(ch, 0);
		REQ(ch, simple_stmt);
		for (j = 0; j < NCH(ch); j += 2) {
		    /* statement terminates with a semi-colon ';' */
		    if (NCH(CHILD(ch, j)) == 0) {
			assert((j + 1) == NCH(ch));
			break;
		    }
		    s = ast_for_stmt(c, CHILD(ch, j));
		    if (!s)
			return NULL;
		    asdl_seq_SET(seq, pos++, s);
		}
	    }
	}
    }
    assert(pos == seq->size);
    return seq;
}

static stmt_ty
ast_for_if_stmt(struct compiling *c, const node *n)
{
    /* if_stmt: 'if' test ':' suite ('elif' test ':' suite)*
       ['else' ':' suite]
    */
    char *s;

    REQ(n, if_stmt);

    if (NCH(n) == 4) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, CHILD(n, 3)); 
        if (!suite_seq)
            return NULL;
            
	return If(expression, suite_seq, NULL, LINENO(n), n->n_col_offset, c->c_arena);
    }

    s = STR(CHILD(n, 4));
    /* s[2], the third character in the string, will be
       's' for el_s_e, or
       'i' for el_i_f
    */
    if (s[2] == 's') {
        expr_ty expression;
        asdl_seq *seq1, *seq2;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        seq1 = ast_for_suite(c, CHILD(n, 3));
        if (!seq1)
            return NULL;
        seq2 = ast_for_suite(c, CHILD(n, 6));
        if (!seq2)
            return NULL;

	return If(expression, seq1, seq2, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (s[2] == 'i') {
	int i, n_elif, has_else = 0;
	asdl_seq *orelse = NULL;
	n_elif = NCH(n) - 4;
        /* must reference the child n_elif+1 since 'else' token is third,
           not fourth, child from the end. */
	if (TYPE(CHILD(n, (n_elif + 1))) == NAME
	    && STR(CHILD(n, (n_elif + 1)))[2] == 's') {
	    has_else = 1;
	    n_elif -= 3;
	}
	n_elif /= 4;

	if (has_else) {
            expr_ty expression;
            asdl_seq *seq1, *seq2;

	    orelse = asdl_seq_new(1, c->c_arena);
	    if (!orelse)
		return NULL;
            expression = ast_for_expr(c, CHILD(n, NCH(n) - 6));
            if (!expression)
                return NULL;
            seq1 = ast_for_suite(c, CHILD(n, NCH(n) - 4));
            if (!seq1)
                return NULL;
            seq2 = ast_for_suite(c, CHILD(n, NCH(n) - 1));
            if (!seq2)
                return NULL;

	    asdl_seq_SET(orelse, 0, If(expression, seq1, seq2, 
				       LINENO(CHILD(n, NCH(n) - 6)), CHILD(n, NCH(n) - 6)->n_col_offset,
                                       c->c_arena));
	    /* the just-created orelse handled the last elif */
	    n_elif--;
	}

	for (i = 0; i < n_elif; i++) {
	    int off = 5 + (n_elif - i - 1) * 4;
            expr_ty expression;
            asdl_seq *suite_seq;
	    asdl_seq *new = asdl_seq_new(1, c->c_arena);
	    if (!new)
		return NULL;
            expression = ast_for_expr(c, CHILD(n, off));
            if (!expression)
                return NULL;
            suite_seq = ast_for_suite(c, CHILD(n, off + 2));
            if (!suite_seq)
                return NULL;

	    asdl_seq_SET(new, 0,
			 If(expression, suite_seq, orelse, 
			    LINENO(CHILD(n, off)), CHILD(n, off)->n_col_offset, c->c_arena));
	    orelse = new;
	}
	return If(ast_for_expr(c, CHILD(n, 1)),
		  ast_for_suite(c, CHILD(n, 3)),
		  orelse, LINENO(n), n->n_col_offset, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "unexpected token in 'if' statement: %s", s);
    return NULL;
}

static stmt_ty
ast_for_while_stmt(struct compiling *c, const node *n)
{
    /* while_stmt: 'while' test ':' suite ['else' ':' suite] */
    REQ(n, while_stmt);

    if (NCH(n) == 4) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, CHILD(n, 3));
        if (!suite_seq)
            return NULL;
	return While(expression, suite_seq, NULL, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (NCH(n) == 7) {
        expr_ty expression;
        asdl_seq *seq1, *seq2;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        seq1 = ast_for_suite(c, CHILD(n, 3));
        if (!seq1)
            return NULL;
        seq2 = ast_for_suite(c, CHILD(n, 6));
        if (!seq2)
            return NULL;

	return While(expression, seq1, seq2, LINENO(n), n->n_col_offset, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "wrong number of tokens for 'while' statement: %d",
                 NCH(n));
    return NULL;
}

static stmt_ty
ast_for_for_stmt(struct compiling *c, const node *n)
{
    asdl_seq *_target, *seq = NULL, *suite_seq;
    expr_ty expression;
    expr_ty target;
    /* for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite] */
    REQ(n, for_stmt);

    if (NCH(n) == 9) {
	seq = ast_for_suite(c, CHILD(n, 8));
        if (!seq)
            return NULL;
    }

    _target = ast_for_exprlist(c, CHILD(n, 1), Store);
    if (!_target)
        return NULL;
    if (asdl_seq_LEN(_target) == 1)
	target = asdl_seq_GET(_target, 0);
    else
	target = Tuple(_target, Store, LINENO(n), n->n_col_offset, c->c_arena);

    expression = ast_for_testlist(c, CHILD(n, 3));
    if (!expression)
        return NULL;
    suite_seq = ast_for_suite(c, CHILD(n, 5));
    if (!suite_seq)
        return NULL;

    return For(target, expression, suite_seq, seq, LINENO(n), n->n_col_offset, c->c_arena);
}

static excepthandler_ty
ast_for_except_clause(struct compiling *c, const node *exc, node *body)
{
    /* except_clause: 'except' [test [',' test]] */
    REQ(exc, except_clause);
    REQ(body, suite);

    if (NCH(exc) == 1) {
        asdl_seq *suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

	return excepthandler(NULL, NULL, suite_seq, c->c_arena);
    }
    else if (NCH(exc) == 2) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(exc, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

	return excepthandler(expression, NULL, suite_seq, c->c_arena);
    }
    else if (NCH(exc) == 4) {
        asdl_seq *suite_seq;
        expr_ty expression;
	expr_ty e = ast_for_expr(c, CHILD(exc, 3));
	if (!e)
            return NULL;
	if (!set_context(e, Store, CHILD(exc, 3)))
            return NULL;
        expression = ast_for_expr(c, CHILD(exc, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

	return excepthandler(expression, e, suite_seq, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "wrong number of children for 'except' clause: %d",
                 NCH(exc));
    return NULL;
}

static stmt_ty
ast_for_try_stmt(struct compiling *c, const node *n)
{
    const int nch = NCH(n);
    int n_except = (nch - 3)/3;
    asdl_seq *body, *orelse = NULL, *finally = NULL;

    REQ(n, try_stmt);

    body = ast_for_suite(c, CHILD(n, 2));
    if (body == NULL)
        return NULL;

    if (TYPE(CHILD(n, nch - 3)) == NAME) {
        if (strcmp(STR(CHILD(n, nch - 3)), "finally") == 0) {
            if (nch >= 9 && TYPE(CHILD(n, nch - 6)) == NAME) {
                /* we can assume it's an "else",
                   because nch >= 9 for try-else-finally and
                   it would otherwise have a type of except_clause */
                orelse = ast_for_suite(c, CHILD(n, nch - 4));
                if (orelse == NULL)
                    return NULL;
                n_except--;
            }

            finally = ast_for_suite(c, CHILD(n, nch - 1));
            if (finally == NULL)
                return NULL;
            n_except--;
        }
        else {
            /* we can assume it's an "else",
               otherwise it would have a type of except_clause */
            orelse = ast_for_suite(c, CHILD(n, nch - 1));
            if (orelse == NULL)
                return NULL;
            n_except--;
        }
    }
    else if (TYPE(CHILD(n, nch - 3)) != except_clause) {
        ast_error(n, "malformed 'try' statement");
        return NULL;
    }
    
    if (n_except > 0) {
	int i;
	stmt_ty except_st;
        /* process except statements to create a try ... except */
        asdl_seq *handlers = asdl_seq_new(n_except, c->c_arena);
        if (handlers == NULL)
            return NULL;

        for (i = 0; i < n_except; i++) {
            excepthandler_ty e = ast_for_except_clause(c, CHILD(n, 3 + i * 3),
                                                       CHILD(n, 5 + i * 3));
            if (!e)
                return NULL;
            asdl_seq_SET(handlers, i, e);
        }

	except_st = TryExcept(body, handlers, orelse, LINENO(n), n->n_col_offset, c->c_arena);
        if (!finally)
	    return except_st;

        /* if a 'finally' is present too, we nest the TryExcept within a
           TryFinally to emulate try ... except ... finally */
	body = asdl_seq_new(1, c->c_arena);
	if (body == NULL)
	    return NULL;
	asdl_seq_SET(body, 0, except_st);
    }

    /* must be a try ... finally (except clauses are in body, if any exist) */
    assert(finally != NULL);
    return TryFinally(body, finally, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_with_var(struct compiling *c, const node *n)
{
    REQ(n, with_var);
    if (strcmp(STR(CHILD(n, 0)), "as") != 0) {
        ast_error(n, "expected \"with [expr] as [var]\"");
        return NULL;
    }
    return ast_for_expr(c, CHILD(n, 1));
}

/* with_stmt: 'with' test [ with_var ] ':' suite */
static stmt_ty
ast_for_with_stmt(struct compiling *c, const node *n)
{
    expr_ty context_expr, optional_vars = NULL;
    int suite_index = 3;    /* skip 'with', test, and ':' */
    asdl_seq *suite_seq;

    assert(TYPE(n) == with_stmt);
    context_expr = ast_for_expr(c, CHILD(n, 1));
    if (TYPE(CHILD(n, 2)) == with_var) {
        optional_vars = ast_for_with_var(c, CHILD(n, 2));

        if (!optional_vars) {
            return NULL;
        }
	if (!set_context(optional_vars, Store, n)) {
	    return NULL;
	}
        suite_index = 4;
    }

    suite_seq = ast_for_suite(c, CHILD(n, suite_index));
    if (!suite_seq) {
        return NULL;
    }
    return With(context_expr, optional_vars, suite_seq, LINENO(n), 
		n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_classdef(struct compiling *c, const node *n)
{
    /* classdef: 'class' NAME ['(' testlist ')'] ':' suite */
    asdl_seq *bases, *s;
    
    REQ(n, classdef);

    if (!strcmp(STR(CHILD(n, 1)), "None")) {
	    ast_error(n, "assignment to None");
	    return NULL;
    }

    if (NCH(n) == 4) {
        s = ast_for_suite(c, CHILD(n, 3));
        if (!s)
            return NULL;
	return ClassDef(NEW_IDENTIFIER(CHILD(n, 1)), NULL, s, LINENO(n), n->n_col_offset,
                        c->c_arena);
    }
    /* check for empty base list */
    if (TYPE(CHILD(n,3)) == RPAR) {
	s = ast_for_suite(c, CHILD(n,5));
	if (!s)
		return NULL;
	return ClassDef(NEW_IDENTIFIER(CHILD(n, 1)), NULL, s, LINENO(n), n->n_col_offset,
                        c->c_arena);
    }

    /* else handle the base class list */
    bases = ast_for_class_bases(c, CHILD(n, 3));
    if (!bases)
        return NULL;

    s = ast_for_suite(c, CHILD(n, 6));
    if (!s)
        return NULL;
    return ClassDef(NEW_IDENTIFIER(CHILD(n, 1)), bases, s, LINENO(n), n->n_col_offset,
                    c->c_arena);
}

static stmt_ty
ast_for_stmt(struct compiling *c, const node *n)
{
    if (TYPE(n) == stmt) {
	assert(NCH(n) == 1);
	n = CHILD(n, 0);
    }
    if (TYPE(n) == simple_stmt) {
	assert(num_stmts(n) == 1);
	n = CHILD(n, 0);
    }
    if (TYPE(n) == small_stmt) {
	REQ(n, small_stmt);
	n = CHILD(n, 0);
	/* small_stmt: expr_stmt | print_stmt  | del_stmt | pass_stmt
	             | flow_stmt | import_stmt | global_stmt | exec_stmt
                     | assert_stmt
	*/
	switch (TYPE(n)) {
            case expr_stmt:
                return ast_for_expr_stmt(c, n);
            case print_stmt:
                return ast_for_print_stmt(c, n);
            case del_stmt:
                return ast_for_del_stmt(c, n);
            case pass_stmt:
                return Pass(LINENO(n), n->n_col_offset, c->c_arena);
            case flow_stmt:
                return ast_for_flow_stmt(c, n);
            case import_stmt:
                return ast_for_import_stmt(c, n);
            case global_stmt:
                return ast_for_global_stmt(c, n);
            case exec_stmt:
                return ast_for_exec_stmt(c, n);
            case assert_stmt:
                return ast_for_assert_stmt(c, n);
            default:
                PyErr_Format(PyExc_SystemError,
                             "unhandled small_stmt: TYPE=%d NCH=%d\n",
                             TYPE(n), NCH(n));
                return NULL;
        }
    }
    else {
        /* compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt
	                | funcdef | classdef
	*/
	node *ch = CHILD(n, 0);
	REQ(n, compound_stmt);
	switch (TYPE(ch)) {
            case if_stmt:
                return ast_for_if_stmt(c, ch);
            case while_stmt:
                return ast_for_while_stmt(c, ch);
            case for_stmt:
                return ast_for_for_stmt(c, ch);
            case try_stmt:
                return ast_for_try_stmt(c, ch);
            case with_stmt:
                return ast_for_with_stmt(c, ch);
            case funcdef:
                return ast_for_funcdef(c, ch);
            case classdef:
                return ast_for_classdef(c, ch);
            default:
                PyErr_Format(PyExc_SystemError,
                             "unhandled small_stmt: TYPE=%d NCH=%d\n",
                             TYPE(n), NCH(n));
                return NULL;
	}
    }
}

static PyObject *
parsenumber(const char *s)
{
	const char *end;
	long x;
	double dx;
#ifndef WITHOUT_COMPLEX
	Py_complex c;
	int imflag;
#endif

	errno = 0;
	end = s + strlen(s) - 1;
#ifndef WITHOUT_COMPLEX
	imflag = *end == 'j' || *end == 'J';
#endif
	if (*end == 'l' || *end == 'L')
		return PyLong_FromString((char *)s, (char **)0, 0);
	if (s[0] == '0') {
		x = (long) PyOS_strtoul((char *)s, (char **)&end, 0);
 		if (x < 0 && errno == 0) {
	 			return PyLong_FromString((char *)s,
							 (char **)0,
							 0);
		}
	}
	else
		x = PyOS_strtol((char *)s, (char **)&end, 0);
	if (*end == '\0') {
		if (errno != 0)
			return PyLong_FromString((char *)s, (char **)0, 0);
		return PyInt_FromLong(x);
	}
	/* XXX Huge floats may silently fail */
#ifndef WITHOUT_COMPLEX
	if (imflag) {
		c.real = 0.;
		PyFPE_START_PROTECT("atof", return 0)
		c.imag = PyOS_ascii_atof(s);
		PyFPE_END_PROTECT(c)
		return PyComplex_FromCComplex(c);
	}
	else
#endif
	{
		PyFPE_START_PROTECT("atof", return 0)
		dx = PyOS_ascii_atof(s);
		PyFPE_END_PROTECT(dx)
		return PyFloat_FromDouble(dx);
	}
}

static PyObject *
decode_utf8(const char **sPtr, const char *end, char* encoding)
{
#ifndef Py_USING_UNICODE
	Py_FatalError("decode_utf8 should not be called in this build.");
        return NULL;
#else
	PyObject *u, *v;
	char *s, *t;
	t = s = (char *)*sPtr;
	/* while (s < end && *s != '\\') s++; */ /* inefficient for u".." */
	while (s < end && (*s & 0x80)) s++;
	*sPtr = s;
	u = PyUnicode_DecodeUTF8(t, s - t, NULL);
	if (u == NULL)
		return NULL;
	v = PyUnicode_AsEncodedString(u, encoding, NULL);
	Py_DECREF(u);
	return v;
#endif
}

static PyObject *
decode_unicode(const char *s, size_t len, int rawmode, const char *encoding)
{
	PyObject *v, *u;
	char *buf;
	char *p;
	const char *end;
	if (encoding == NULL) {
	     	buf = (char *)s;
		u = NULL;
	} else if (strcmp(encoding, "iso-8859-1") == 0) {
	     	buf = (char *)s;
		u = NULL;
	} else {
		/* "\XX" may become "\u005c\uHHLL" (12 bytes) */
		u = PyString_FromStringAndSize((char *)NULL, len * 4);
		if (u == NULL)
			return NULL;
		p = buf = PyString_AsString(u);
		end = s + len;
		while (s < end) {
			if (*s == '\\') {
				*p++ = *s++;
				if (*s & 0x80) {
					strcpy(p, "u005c");
					p += 5;
				}
			}
			if (*s & 0x80) { /* XXX inefficient */
				PyObject *w;
				char *r;
				int rn, i;
				w = decode_utf8(&s, end, "utf-16-be");
				if (w == NULL) {
					Py_DECREF(u);
					return NULL;
				}
				r = PyString_AsString(w);
				rn = PyString_Size(w);
				assert(rn % 2 == 0);
				for (i = 0; i < rn; i += 2) {
					sprintf(p, "\\u%02x%02x",
						r[i + 0] & 0xFF,
						r[i + 1] & 0xFF);
					p += 6;
				}
				Py_DECREF(w);
			} else {
				*p++ = *s++;
			}
		}
		len = p - buf;
		s = buf;
	}
	if (rawmode)
		v = PyUnicode_DecodeRawUnicodeEscape(s, len, NULL);
	else
		v = PyUnicode_DecodeUnicodeEscape(s, len, NULL);
	Py_XDECREF(u);
	return v;
}

/* s is a Python string literal, including the bracketing quote characters,
 * and r &/or u prefixes (if any), and embedded escape sequences (if any).
 * parsestr parses it, and returns the decoded Python string object.
 */
static PyObject *
parsestr(const char *s, const char *encoding)
{
	size_t len;
	int quote = Py_CHARMASK(*s);
	int rawmode = 0;
	int need_encoding;
	int unicode = 0;

	if (isalpha(quote) || quote == '_') {
		if (quote == 'u' || quote == 'U') {
			quote = *++s;
			unicode = 1;
		}
		if (quote == 'r' || quote == 'R') {
			quote = *++s;
			rawmode = 1;
		}
	}
	if (quote != '\'' && quote != '\"') {
		PyErr_BadInternalCall();
		return NULL;
	}
	s++;
	len = strlen(s);
	if (len > INT_MAX) {
		PyErr_SetString(PyExc_OverflowError, 
				"string to parse is too long");
		return NULL;
	}
	if (s[--len] != quote) {
		PyErr_BadInternalCall();
		return NULL;
	}
	if (len >= 4 && s[0] == quote && s[1] == quote) {
		s += 2;
		len -= 2;
		if (s[--len] != quote || s[--len] != quote) {
			PyErr_BadInternalCall();
			return NULL;
		}
	}
#ifdef Py_USING_UNICODE
	if (unicode || Py_UnicodeFlag) {
		return decode_unicode(s, len, rawmode, encoding);
	}
#endif
	need_encoding = (encoding != NULL &&
			 strcmp(encoding, "utf-8") != 0 &&
			 strcmp(encoding, "iso-8859-1") != 0);
	if (rawmode || strchr(s, '\\') == NULL) {
		if (need_encoding) {
#ifndef Py_USING_UNICODE
			/* This should not happen - we never see any other
			   encoding. */
			Py_FatalError("cannot deal with encodings in this build.");
#else
			PyObject *v, *u = PyUnicode_DecodeUTF8(s, len, NULL);
			if (u == NULL)
				return NULL;
			v = PyUnicode_AsEncodedString(u, encoding, NULL);
			Py_DECREF(u);
			return v;
#endif
		} else {
			return PyString_FromStringAndSize(s, len);
		}
	}

	return PyString_DecodeEscape(s, len, NULL, unicode,
				     need_encoding ? encoding : NULL);
}

/* Build a Python string object out of a STRING atom.  This takes care of
 * compile-time literal catenation, calling parsestr() on each piece, and
 * pasting the intermediate results together.
 */
static PyObject *
parsestrplus(struct compiling *c, const node *n)
{
	PyObject *v;
	int i;
	REQ(CHILD(n, 0), STRING);
	if ((v = parsestr(STR(CHILD(n, 0)), c->c_encoding)) != NULL) {
		/* String literal concatenation */
		for (i = 1; i < NCH(n); i++) {
			PyObject *s;
			s = parsestr(STR(CHILD(n, i)), c->c_encoding);
			if (s == NULL)
				goto onError;
			if (PyString_Check(v) && PyString_Check(s)) {
				PyString_ConcatAndDel(&v, s);
				if (v == NULL)
				    goto onError;
			}
#ifdef Py_USING_UNICODE
			else {
				PyObject *temp = PyUnicode_Concat(v, s);
				Py_DECREF(s);
				Py_DECREF(v);
				v = temp;
				if (v == NULL)
				    goto onError;
			}
#endif
		}
	}
	return v;

 onError:
	Py_XDECREF(v);
	return NULL;
}