mirror of https://github.com/lark-parser/lark.git
64 lines
1.2 KiB
Python
64 lines
1.2 KiB
Python
#
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# This example shows how to write a basic calculator with variables.
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#
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from lark import Lark, InlineTransformer
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calc_grammar = """
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?start: sum
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| NAME "=" sum -> assign_var
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?sum: product
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| sum "+" product -> add
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| sum "-" product -> sub
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?product: atom
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| product "*" atom -> mul
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| product "/" atom -> div
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?atom: /[\d.]+/ -> number
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| "-" atom -> neg
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| NAME -> var
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| "(" sum ")"
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NAME: /[a-zA-Z]\w*/
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WS.ignore: /\s+/
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"""
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class CalculateTree(InlineTransformer):
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from operator import add, sub, mul, truediv as div, neg
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number = float
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def __init__(self):
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self.vars = {}
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def assign_var(self, name, value):
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self.vars[name] = value
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return value
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def var(self, name):
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return self.vars[name]
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calc_parser = Lark(calc_grammar, parser='lalr', transformer=CalculateTree())
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calc = calc_parser.parse
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def main():
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while True:
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try:
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s = raw_input('> ')
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except EOFError:
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break
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print(calc(s))
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def test():
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# print calc("a=(1+2)")
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print(calc("a = 1+2"))
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print(calc("1+a*-3"))
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if __name__ == '__main__':
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test()
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# main()
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