mirror of https://github.com/python/cpython
34 lines
1.5 KiB
Markdown
34 lines
1.5 KiB
Markdown
|
# Tooling to generate interpreters
|
||
|
|
|
||
|
|
What's currently here:
|
||
|
|
|
||
|
|
- lexer.py: lexer for C, originally written by Mark Shannon
|
||
|
|
- plexer.py: OO interface on top of lexer.py; main class: `PLexer`
|
||
|
|
- parser.py: Parser for instruction definition DSL; main class `Parser`
|
||
|
|
- `generate_cases.py`: driver script to read `Python/bytecodes.c` and
|
||
|
|
write `Python/generated_cases.c.h`
|
||
|
|
|
||
|
|
The DSL for the instruction definitions in `Python/bytecodes.c` is described
|
||
|
|
[here](https://github.com/faster-cpython/ideas/blob/main/3.12/interpreter_definition.md).
|
||
|
|
Note that there is some dummy C code at the top and bottom of the file
|
||
|
|
to fool text editors like VS Code into believing this is valid C code.
|
||
|
|
|
||
|
|
## A bit about the parser
|
||
|
|
|
||
|
|
The parser class uses a pretty standard recursive descent scheme,
|
||
|
|
but with unlimited backtracking.
|
||
|
|
The `PLexer` class tokenizes the entire input before parsing starts.
|
||
|
|
We do not run the C preprocessor.
|
||
|
|
Each parsing method returns either an AST node (a `Node` instance)
|
||
|
|
or `None`, or raises `SyntaxError` (showing the error in the C source).
|
||
|
|
|
||
|
|
Most parsing methods are decorated with `@contextual`, which automatically
|
||
|
|
resets the tokenizer input position when `None` is returned.
|
||
|
|
Parsing methods may also raise `SyntaxError`, which is irrecoverable.
|
||
|
|
When a parsing method returns `None`, it is possible that after backtracking
|
||
|
|
a different parsing method returns a valid AST.
|
||
|
|
|
||
|
|
Neither the lexer nor the parsers are complete or fully correct.
|
||
|
|
Most known issues are tersely indicated by `# TODO:` comments.
|
||
|
|
We plan to fix issues as they become relevant.
|