def goSequent() :
"""goSequent helps a user interactively type a sequent to be proved,
formats it in cnf (where the goal prop is negated),
and writes it as a string to a textfile.
The string has the format, D1 D2 ... Dn,
where D ::= [F1, F2, ... Fm]
F ::= "p" | "-p"
where p is a string of letters
Example: the input, p->r, q->r |- (p | q) -> r,
is mapped to the cnf form,
[['-p', 'r'], ['-q', 'r'], ['p', 'q'], ['-r']]
and the string,
[-p,r][-q,r][p,q][-r]
is written to the output file that the user requests.
"""
import Parse
premises = True
answer = []
while premises:
text = raw_input("Type premise (or |-): ").strip()
if text == "|-" :
premises = False
else :
prop = cnf( Parse.parse(Parse.scan(text)) )
answer = answer + prop
text = raw_input("Type goal prop: ")
not_text = "-(" + text + ")"
not_goal = cnf( Parse.parse(Parse.scan(not_text)) )
answer = answer + not_goal
print "clauses are:", answer
print
filename = raw_input("Type name of destination file: ")
output = open(filename, "w")
textline = ""
for clause in answer :
textline = textline + "["
items = ""
for literal in clause :
items = items + "," + literal
if items != "" :
items = items[1:] # forget leading comma
textline = textline + items + "]"
print "wrote to", filename + ":", textline
output.write(textline)
output.close
if c == NOT :
opposite = prim[1:]
else :
opposite = NOT + prim
if opposite in d :
return True
return False
if __name__ == '__main__':
#def main():
"""main lets you test the algorithm with interactive input"""
import Parse
text = raw_input("Type a proposition: ")
print
prop0 = Parse.parse(Parse.scan(text))
print "parse tree: "
print prop0
print
prop1 = removeImplications(prop0)
print "-> removed:"
print prop1
print
prop2 = moveNegations(prop1)
print "- shifted inwards:"
print prop2
print
prop3 = makeIntoCNF(prop2)
print "cnf:"
print prop3
print