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import math
from parsley import makeGrammar
def calculate(start, pairs):
result = start
for op, value in pairs:
if op == '+':
result += value
elif op == '-':
result -= value
elif op == '*':
result *= value
elif op == '/':
result /= value
return result
calcGrammar = """
number = <digit+>:ds -> int(ds)
parens = '(' ws expr:e ws ')' -> e
value = number | parens
ws = ' '*
add = '+' ws expr2:n -> ('+', n)
sub = '-' ws expr2:n -> ('-', n)
mul = '*' ws value:n -> ('*', n)
div = '/' ws value:n -> ('/', n)
addsub = ws (add | sub)
muldiv = ws (mul | div)
expr = expr2:left addsub*:right -> calculate(left, right)
expr2 = value:left muldiv*:right -> calculate(left, right)
"""
Calc = makeGrammar(calcGrammar, {"calculate": calculate}, name="Calc")
calcGrammarEx = """
value = super | constant
constant = 'pi' -> math.pi
| 'e' -> math.e
"""
CalcEx = makeGrammar(calcGrammarEx, {"math": math}, name="CalcEx",
extends=Calc)
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