Mercurial > lbo > hg > pcombinators
view pcombinators/arith_test.py @ 66:b9ed614fc42f draft
Add Peek and Lazy parsers and fix bugs in Repeat/Sequence
author | Lewin Bormann <lbo@spheniscida.de> |
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date | Sat, 25 May 2019 14:46:01 +0200 |
parents | f2515a9dc9ef |
children |
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#!/usr/bin/env python3 # -*- coding: utf-8 -*- """ Let's test the combinators in a real world application! @author: lbo """ from pcombinators.state import ParseState from pcombinators.combinators import * from pcombinators.primitives import * def Operator(set): """An operator or parenthesis.""" return OneOf(set) def Parens(): """Parentheses contain a term.""" return (Operator('(') + Term() + Operator(')')) >> (lambda l: l[1]) def Variable(): """A variable consists of several letters.""" return Regex('[a-zA-Z]+[0-9]*') def Atom(): """An atom is a variable or a float or a parentheses term.""" return (Variable() | Parens() | Float()) def Product(): return OptimisticSequence(Power(), Operator('*/') + Lazy(Product)) >> operator_result_to_tuple class Power(Parser): ops = Operator('^') def __init__(self): self.p = OptimisticSequence(Lazy(Atom), self.ops + self) >> operator_result_to_tuple def parse(self, st): return self.p.parse(st) class Term(Parser): ops = Operator('+-') def __init__(self): self.p = OptimisticSequence(Product(), self.ops + self) >> operator_result_to_tuple 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. return self.p.parse(st) 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 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(ParseState(expr.replace(' ', ''))) if parsed is None: print('Parse error :(', st) return return pretty_print(parsed)