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#
# simpleArith.py
#
# Example of defining an arithmetic expression parser using
# the infixNotation helper method in pyparsing.
#
# Copyright 2006, by Paul McGuire
#
import sys
from pyparsing import *
ppc = pyparsing_common
ParserElement.enablePackrat()
sys.setrecursionlimit(3000)
integer = ppc.integer
variable = Word(alphas, exact=1)
operand = integer | variable
expop = Literal("^")
signop = oneOf("+ -")
multop = oneOf("* /")
plusop = oneOf("+ -")
factop = Literal("!")
# To use the infixNotation helper:
# 1. Define the "atom" operand term of the grammar.
# For this simple grammar, the smallest operand is either
# an integer or a variable. This will be the first argument
# to the infixNotation method.
# 2. Define a list of tuples for each level of operator
# precedence. Each tuple is of the form
# (opExpr, numTerms, rightLeftAssoc, parseAction), where
# - opExpr is the pyparsing expression for the operator;
# may also be a string, which will be converted to a Literal
# - numTerms is the number of terms for this operator (must
# be 1 or 2)
# - rightLeftAssoc is the indicator whether the operator is
# right or left associative, using the pyparsing-defined
# constants opAssoc.RIGHT and opAssoc.LEFT.
# - parseAction is the parse action to be associated with
# expressions matching this operator expression (the
# parse action tuple member may be omitted)
# 3. Call infixNotation passing the operand expression and
# the operator precedence list, and save the returned value
# as the generated pyparsing expression. You can then use
# this expression to parse input strings, or incorporate it
# into a larger, more complex grammar.
#
expr = infixNotation(
operand,
[
(factop, 1, opAssoc.LEFT),
(expop, 2, opAssoc.RIGHT),
(signop, 1, opAssoc.RIGHT),
(multop, 2, opAssoc.LEFT),
(plusop, 2, opAssoc.LEFT),
],
)
test = [
"9 + 2 + 3",
"9 + 2 * 3",
"(9 + 2) * 3",
"(9 + -2) * 3",
"(9 + -2) * 3^2^2",
"(9! + -2) * 3^2^2",
"M*X + B",
"M*(X + B)",
"1+2*-3^4*5+-+-6",
"(a + b)",
"((a + b))",
"(((a + b)))",
"((((a + b))))",
"((((((((((((((a + b))))))))))))))",
]
for t in test:
print(t)
print(expr.parseString(t))
print("")