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A Python 3 compatible fork of https://launchpad.net/pymeta
License: Other
This project forked from wbond/pymeta3
A Python 3 compatible fork of https://launchpad.net/pymeta
License: Other
======== PyMeta3 ======== -------------------------------------------- A Pattern-Matching Language Based on Python -------------------------------------------- This is a fork of PyMeta 0.5.0 that supports Python 2 and 3. Installation ============ pip install PyMeta3 Summary ======= PyMeta is an implementation of OMeta, an object-oriented pattern-matching language developed by Alessandro Warth (http://www.cs.ucla.edu/~awarth/ometa/). PyMeta provides a compact syntax based on Parsing Expression Grammars (PEGs) for common lexing, parsing and tree-transforming activities in a way that's easy to reason about for Python programmers. How It Works ============ PyMeta compiles a grammar to a Python class, with the rules as methods. The rules specify parsing expressions, which consume input and return values if they succeed in matching. Basic syntax ~~~~~~~~~~~~~~~~ ``foo ::= ....`` Define a rule named foo. ``expr1 expr2`` Match expr1, and then match expr2 if it succeeds, returning the value of expr2. Like Python's ``and``. ``expr1 | expr2`` Try to match expr1 --- if it fails, match expr2 instead. Like Python's ``or``. ``expr*`` Match expr zero or more times, returning a list of matches. ``expr+`` Match expr one or more times, returning a list of matches. ``expr?`` Try to match expr. Returns None if it fails to match. ``~expr`` Fail if the next item in the input matches expr. ``<ruleName>`` Call the rule ``ruleName``. ``'x'`` Match the literal character 'x'. ``expr:name`` Bind the result of expr to the local variable ``name``. ``=> pythonExpression`` Evaluate the given Python expression and return its result. Comments like Python comments are supported as well, starting with # and extending to the end of the line. Interface ========= The starting point for defining a new grammar is ``pymeta.grammar.OMeta.makeGrammar``, which takes a grammar definition and a dict of variable bindings for its embedded expressions and produces a Python class. Grammars can be subclassed as usual, and makeGrammar can be called on these classes to override rules and provide new ones. To invoke a grammar rule, call ``grammarObject.apply()`` with its name. Example Usage ============= >>> from pymeta.grammar import OMeta >>> exampleGrammar = """ ones ::= '1' '1' => 1 twos ::= '2' '2' => 2 stuff ::= (<ones> | <twos>)+ """ >>> Example = OMeta.makeGrammar(exampleGrammar, {}) >>> g = Example("11221111") >>> result, error = g.apply("stuff") >>> result [1, 2, 1, 1]
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