#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# rule_engine/parser/base.py
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import threading
import ply.lex as lex
import ply.yacc as yacc
[docs]
class ParserBase(object):
"""
A base class for parser objects to inherit from. This does not provide any
grammar related definitions.
"""
precedence = ()
"""The precedence for operators."""
tokens = ()
reserved_words = {}
"""
A mapping of literal words which are reserved to their corresponding grammar
names.
"""
__mutex = threading.Lock()
[docs]
def __init__(self, debug=False):
"""
:param bool debug: Whether or not to enable debugging features when
using the ply API.
"""
self.debug = debug
self.context = None
# Build the lexer and parser
self._lexer = lex.lex(module=self, debug=self.debug)
self._parser = yacc.yacc(module=self, debug=self.debug, write_tables=self.debug)
[docs]
def parse(self, text, context, **kwargs):
"""
Parse the specified text in an abstract syntax tree of nodes that can later be evaluated. This is done in two
phases. First, the syntax is parsed and a tree of deferred / uninitialized AST nodes are constructed. Next each
node is built recursively using it's respective :py:meth:`rule_engine.ast.ASTNodeBase.build`.
:param str text: The grammar text to parse into an AST.
:param context: A context for specifying parsing and evaluation options.
:type context: :py:class:`~rule_engine.engine.Context`
:return: The parsed AST statement.
:rtype: :py:class:`~rule_engine.ast.Statement`
"""
kwargs['lexer'] = kwargs.pop('lexer', self._lexer)
with self.__mutex:
self.context = context
# phase 1: parse the string into a tree of deferred nodes
result = self._parser.parse(text, **kwargs)
self.context = None
# phase 2: initialize each AST node recursively, providing them with an opportunity to define assignments
return result.build()