parser/parser.py

   1 import os
   2 from parsimonious import Grammar, NodeVisitor
   3
   4
   5 # cache
   6 _grammar = None
   7
   8
   9 def load_grammar():
  10     global _grammar
  11     parser_dir = os.path.dirname(__file__)
  12     with open(os.path.join(parser_dir, 'grammar.ebnf'), 'rt') as grammar_file:
  13         grammar_text = grammar_file.read()
  14     _grammar = Grammar(grammar_text)
  15
  16
  17 def parse(input):
  18     if _grammar is None:
  19         load_grammar()
  20     return _grammar.parse(input)
  21
  22
  23 def cleanup_children(visited_children):
  24     children = [c for c in visited_children if c]
  25     if len(children) == 1:
  26         return children[0]
  27     else:
  28         return children
  29
  30
  31 class Compiler(NodeVisitor):
  32     def generic_visit(self, node, visited_children):
  33         return cleanup_children(visited_children)
  34
  35     def visit_or_expression(self, node, visited_children):
  36         return ('OR', visited_children[0], visited_children[2])
  37
  38     def visit_and_expression(self, node, visited_children):
  39         return ('AND', visited_children[0], visited_children[2])
  40
  41     def visit_not_expression(self, node, visited_children):
  42         return ('NOT', visited_children[2])
  43
  44     def visit_parens_expression(self, node, visited_children):
  45         return ('PARENS', visited_children[2])
  46
  47     def visit_name(self, node, visited_children):
  48         return ('NAME', node.text)
  49
  50
  51 def compile(tree):
  52     if isinstance(tree, str):
  53         tree = parse(tree)
  54     return Compiler().visit(tree)