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63 lines
1.8 KiB
Python
63 lines
1.8 KiB
Python
import argparse
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import sys
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from typing import Any, Callable, Iterator
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from pegen.build import build_parser
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from pegen.grammar import Grammar, Rule
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argparser = argparse.ArgumentParser(
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prog="pegen", description="Pretty print the AST for a given PEG grammar"
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)
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argparser.add_argument("filename", help="Grammar description")
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class ASTGrammarPrinter:
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def children(self, node: Rule) -> Iterator[Any]:
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for value in node:
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if isinstance(value, list):
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yield from value
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else:
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yield value
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def name(self, node: Rule) -> str:
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if not list(self.children(node)):
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return repr(node)
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return node.__class__.__name__
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def print_grammar_ast(self, grammar: Grammar, printer: Callable[..., None] = print) -> None:
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for rule in grammar.rules.values():
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printer(self.print_nodes_recursively(rule))
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def print_nodes_recursively(self, node: Rule, prefix: str = "", istail: bool = True) -> str:
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children = list(self.children(node))
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value = self.name(node)
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line = prefix + ("└──" if istail else "├──") + value + "\n"
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sufix = " " if istail else "│ "
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if not children:
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return line
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*children, last = children
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for child in children:
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line += self.print_nodes_recursively(child, prefix + sufix, False)
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line += self.print_nodes_recursively(last, prefix + sufix, True)
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return line
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def main() -> None:
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args = argparser.parse_args()
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try:
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grammar, parser, tokenizer = build_parser(args.filename)
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except Exception as err:
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print("ERROR: Failed to parse grammar file", file=sys.stderr)
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sys.exit(1)
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visitor = ASTGrammarPrinter()
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visitor.print_grammar_ast(grammar)
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if __name__ == "__main__":
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main()
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