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