def intersect(cfg, nfa):
ret = CFG()
Nt = cfg.nonterms
St = list(nfa.states)
for _ in range(len(Nt) * len(St)**2 - 1):
ret.addNonterm()
NtInv = { Nt[i]:i for i in range(len(Nt)) }
StInv = { St[i]:i for i in range(len(St)) }
def getNterm(p, A, q):
idx = (NtInv[A]*len(St) + StInv[p])*len(St) + StInv[q]
return ret.nonterms[idx]
ret.start = getNterm(nfa.start, cfg.start, nfa.final)
for lhs, rhsSet in cfg.productions.items():
for rhs in rhsSet:
items = [(x, [], x) for x in St]
for term in rhs:
if term in Nt:
newItems = []
for z in St:
newItems.extend([(x, R + [getNterm(y, term, z)], z) for (x, R, y) in items])
items = newItems
else:
newItems = []
for (x, R, y) in items:
newItems.extend([(x, R + [term], z) for z in nfa.transitions.get(x, {}).get(term, [])])
newItems.extend([(x, R + [term], z) for z in nfa.transitions.get(x, {}).get(WILDCARD, [])])
items = newItems
for (p, R, q) in items:
ret.addProduction(getNterm(p, lhs, q), R)
return ret
if __name__ == '__main__':
class Num:
def __init__(self):
pass
def __str__(self):
return 'Num'
def __repr__(self):
return 'Num'
def __hash__(self):
return hash(0)
def __eq__(self, other):
return isinstance(other, Num)
gram = CFG()
expr = gram.start
term = gram.addNonterm()
fact = gram.addNonterm()
WS = gram.addNonterm()
gram.addProduction(fact, [WS, Num(), WS])
gram.addProduction(fact, [WS, '-', Num(), WS])
gram.addProduction(fact, [WS, '(', expr, ')', WS])
gram.addProduction(term, [term, WS, '*', WS, fact])
gram.addProduction(term, [term, WS, '/', WS, fact])
gram.addProduction(term, [WS, fact, WS])
gram.addProduction(expr, [expr, '+', term])
gram.addProduction(expr, [expr, '-', term])
gram.addProduction(expr, [WS, term, WS])
gram.addProduction(WS, [WS, '\t'])
gram.addProduction(WS, [WS, ' '])
gram.addProduction(WS, [])
