Mercurial > lbo > hg > pcombinators
view pcombinators/arith_test.py @ 31:084d753d5b6a draft
Update parser examples to new model.
author | Lewin Bormann <lbo@spheniscida.de> |
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date | Tue, 21 May 2019 15:46:41 +0200 |
parents | 9fe660fc8efe |
children | 859c9eaa90c2 |
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#!/usr/bin/env python3 # -*- coding: utf-8 -*- """ Let's test the combinators in a real world application! @author: lbo """ from combinators import * from primitives import * def Parens(): """Parentheses contain a term.""" return (Operator('(') + Term() + Operator(')')) >> (lambda l: l[1]) def Variable(): """A variable consists of several letters.""" return Last(Skip(Whitespace()) + Regex('[a-zA-Z]+[0-9]*')) def Atom(): """An atom is a variable or a float or a parentheses term.""" return (Variable() | Parens() | Last(Skip(Whitespace()) + Float())) def Operator(set): """An operator or parenthesis.""" return Last(Skip(Whitespace()) + OneOf(set)) def operator_result_to_tuple(l): if len(l) == 1: return l[0] elif len(l) == 2 and len(l[1]) == 2: return (l[0], l[1][0], l[1][1]) else: # Parse failed if not either 1 or 3. raise Exception("Parse failed: Missing operand") def Power(): return (OptimisticSequence(Atom(), Operator('^') + Atom()) >> operator_result_to_tuple) class Product(Parser): def parse(self, st): # Try to parse an atom, a product operator, and another product. p = OptimisticSequence(Power(), Operator('*/') + Product()) >> operator_result_to_tuple return p.parse(st) class Term(Parser): def parse(self, st): # Try to parse a product, then a sum operator, then another term. # OptimisticSequence will just return a product if there is no sum operator. p = OptimisticSequence(Product(), Operator('+-') + Term()) >> operator_result_to_tuple return p.parse(st) def pretty_print(tpl): # tpl is a (left, op, right) tuple or a scalar. if not isinstance(tpl, tuple): return str(tpl) assert len(tpl) == 3 return '({} {} {})'.format(pretty_print(tpl[0]), tpl[1], pretty_print(tpl[2])) def parse_and_print(expr): """Parse an expression string and return a string of the parsing result.""" parsed, st = Term().parse(ps(expr)) if parsed is None: print('Parse error :(', st) return print(pretty_print(parsed))