def compute_local_first(firsts, alpha):
first_alpha = ContainerSet()
try:
alpha_is_epsilon = alpha.IsEpsilon
except:
alpha_is_epsilon = False
###################################################
# alpha == epsilon ? First(alpha) = { epsilon }
###################################################
# <CODE_HERE> #
if alpha_is_epsilon:
first_alpha.set_epsilon()
return first_alpha
###################################################
###################################################
# alpha = X1 ... XN
# First(X1) subconjunto First(alpha)
# epsilon pertenece a First(X1)...First(Xi) ? First(Xi+1) subconjunto de First(X) y First(alpha)
# epsilon pertenece a First(X1)...First(XN) ? epsilon pertence a First(X) y al First(alpha)
###################################################
# <CODE_HERE> #
change = False
for i in alpha:
if not firsts[i].contains_epsilon:
# epsilon pertenece a First(X1)...First(Xi) ? First(Xi+1) subconjunto de First(X) y First(alpha)
change = True
for j in firsts[i]:
first_alpha.add(j)
if change:
break
if not change:
# epsilon pertenece a First(X1)...First(XN) ? epsilon pertence a First(X) y al First(alpha)
first_alpha.set_epsilon()
###################################################
# First(alpha)
return first_alpha
def remove_useless_non_terminals(G: Grammar):
usefull_non_terminals = ContainerSet()
change = True
while change:
change = False
for production in G.Productions:
for symbol in production.Right:
if symbol.IsNonTerminal:
if symbol not in usefull_non_terminals:
break
else:
change |= usefull_non_terminals.add(production.Left)
# TODO se puede mejorar
for production in G.Productions:
if production.Left not in usefull_non_terminals:
G.Productions.remove(production)
else:
for symbol in production.Right:
if symbol.IsNonTerminal:
if symbol not in usefull_non_terminals:
G.Productions.remove(production)