1  import argparse
       2  import sys
       3  from typing import Any, Callable, Iterator
       4  
       5  from pegen.build import build_parser
       6  from pegen.grammar import Grammar, Rule
       7  
       8  argparser = argparse.ArgumentParser(
       9      prog="pegen", description="Pretty print the AST for a given PEG grammar"
      10  )
      11  argparser.add_argument("filename", help="Grammar description")
      12  
      13  
      14  class ESC[4;38;5;81mASTGrammarPrinter:
      15      def children(self, node: Rule) -> Iterator[Any]:
      16          for value in node:
      17              if isinstance(value, list):
      18                  yield from value
      19              else:
      20                  yield value
      21  
      22      def name(self, node: Rule) -> str:
      23          if not list(self.children(node)):
      24              return repr(node)
      25          return node.__class__.__name__
      26  
      27      def print_grammar_ast(self, grammar: Grammar, printer: Callable[..., None] = print) -> None:
      28          for rule in grammar.rules.values():
      29              printer(self.print_nodes_recursively(rule))
      30  
      31      def print_nodes_recursively(self, node: Rule, prefix: str = "", istail: bool = True) -> str:
      32  
      33          children = list(self.children(node))
      34          value = self.name(node)
      35  
      36          line = prefix + ("└──" if istail else "├──") + value + "\n"
      37          sufix = "   " if istail else "│  "
      38  
      39          if not children:
      40              return line
      41  
      42          *children, last = children
      43          for child in children:
      44              line += self.print_nodes_recursively(child, prefix + sufix, False)
      45          line += self.print_nodes_recursively(last, prefix + sufix, True)
      46  
      47          return line
      48  
      49  
      50  def main() -> None:
      51      args = argparser.parse_args()
      52  
      53      try:
      54          grammar, parser, tokenizer = build_parser(args.filename)
      55      except Exception as err:
      56          print("ERROR: Failed to parse grammar file", file=sys.stderr)
      57          sys.exit(1)
      58  
      59      visitor = ASTGrammarPrinter()
      60      visitor.print_grammar_ast(grammar)
      61  
      62  
      63  if __name__ == "__main__":
      64      main()