PyMeta Pattern-matching language based on OMeta
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Python library Python language

PyMeta Description

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 WorksPyMeta 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 syntaxfoo ::= .... 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. 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.InterfaceThe 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' => 1twos ::= '2' '2' => 2stuff ::= (< ones > | < twos >)+""">>> Example = OMeta.makeGrammar(exampleGrammar, {})>>> g = Example("11221111")>>> result, error = g.apply("stuff")>>> resultProduct's homepage

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