Parse sentential logic w/Parsimonious

for_parsimonious.py

# -*- coding: utf-8 -*-

from parsimonious.grammar import Grammar
try:
    from string import lowercase
except:
    from string import ascii_lowercase as lowercase


def vars_expr():
    """ 
    Generate a string to match all vars (except for "v" -- this is used to denote logical or):
        "a" / "b" / "c" / "d" / "e" / "f" (etc.)
    """
    variables = ['"{}"'.format(l) for l in lowercase if l != 'v']
    return ' / '.join(variables)

g = Grammar(
        """
        EXPR = NEG* OPENPAREN OPERAND SPACE BINOP SPACE OPERAND CLOSEPAREN

        # Character Classes
        SPACE = " "
        NEG = "~" / "!" / "¬"
        OPENPAREN = "("
        VAR = {}
        CLOSEPAREN = ")"
        BINOP = "v" / "&" / "=" / "<->" / "->" / "or"
        
        # Character Class Combinations
        OPERAND = TERM / EXPR
        TERM = NEG* VAR
        """.format(vars_expr()))

g.parse('''!(p & q)''')
g.parse('''!(p v (r -> s))''')
g.parse('''((p v w) <-> !e)''')
g.parse('''((p v !w) & (l <-> x))''')
g.parse('''(p <-> ~(!q -> (r v s)))''')
g.parse('''(p or ~(!q -> (r v s)))''')
g.parse('''!¬(p v ~!~q)''')