def compute_firsts():
from Skoarcery.terminals import Empty, tokens as T
from Skoarcery.nonterminals import nonterminals as N
global FIRST
# do terminals first
for X in T.values():
FIRST(X).add(X)
last = 0
first_len = len(FIRST)
while first_len > last:
last = first_len
for X in N.values():
if X.derives_empty:
FIRST(X).add(Empty)
for R in X.production_rules:
i = -1
n = len(R.production)
# figure out FIRST(X) first
for Yi in R.production:
i += 1
Yi_to_end = R.production[i:]
if len(Yi_to_end) > 0:
S = FIRST(Yi_to_end)
S.update(
everything_but_e(FIRST(Yi))
)
FIRST(X).update(S)
FIRST(Yi_to_end).update(S)
if not Yi.derives_empty:
break
# if we got to the end of the loop without breaking, add Empty
else:
FIRST(X).add(Empty)
first_len = len(FIRST)
def compute_firsts():
from Skoarcery.terminals import Empty, tokens as T
from Skoarcery.nonterminals import nonterminals as N
global FIRST
# do terminals first
for X in T.values():
FIRST(X).add(X)
last = 0
first_len = len(FIRST)
while first_len > last:
last = first_len
for X in N.values():
if X.derives_empty:
FIRST(X).add(Empty)
for R in X.production_rules:
i = -1
n = len(R.production)
# figure out FIRST(X) first
for Yi in R.production:
i += 1
Yi_to_end = R.production[i:]
if len(Yi_to_end) > 0:
S = FIRST(Yi_to_end)
S.update(everything_but_e(FIRST(Yi)))
FIRST(X).update(S)
FIRST(Yi_to_end).update(S)
if not Yi.derives_empty:
break
# if we got to the end of the loop without breaking, add Empty
else:
FIRST(X).add(Empty)
first_len = len(FIRST)
def compute_follows():
from Skoarcery.terminals import EOF, Empty
from Skoarcery.nonterminals import nonterminals as N, SKOAR
global FIRST, FOLLOW
# start symbol gets end symbol
FOLLOW(SKOAR).add(EOF)
# repeat until nothing can be added to any follow set
last = 0
follow_len = len(FOLLOW)
while follow_len > last:
last = follow_len
for X in N.values():
for R in X.production_rules:
A = R.production
# If there is a production [ A -> alpha B beta]:
# everything except <e> in FIRST(beta) is in FOLLOW(B)
# examine each suffix (except last)
n = len(A)
for i in range(0, n - 1):
B = A[i]
if not isinstance(B, Nonterminal):
continue
beta = A[i + 1:]
#print("n: " + str(n) + " i: " + str(i) + " A: " + repr(A) + " beta: " + repr(beta))
S = FIRST(beta)
FOLLOW(B).update(everything_but_e(S))
for i in reversed(range(0, n)):
B = A[i]
if not isinstance(B, Nonterminal):
continue
# we are at the end of the list
if i == n - 1:
FOLLOW(B).update(FOLLOW(X))
continue
beta = A[i + 1:]
S = FIRST(beta)
#print(": FIRST(" + repr(beta) + ") = " + repr(S))
if Empty in S:
FOLLOW(B).update(FOLLOW(X))
else:
break
follow_len = len(FOLLOW)
def compute_follows():
from Skoarcery.terminals import EOF, Empty
from Skoarcery.nonterminals import nonterminals as N, SKOAR
global FIRST, FOLLOW
# start symbol gets end symbol
FOLLOW(SKOAR).add(EOF)
# repeat until nothing can be added to any follow set
last = 0
follow_len = len(FOLLOW)
while follow_len > last:
last = follow_len
for X in N.values():
for R in X.production_rules:
A = R.production
# If there is a production [ A -> alpha B beta]:
# everything except <e> in FIRST(beta) is in FOLLOW(B)
# examine each suffix (except last)
n = len(A)
for i in range(0, n - 1):
B = A[i]
if not isinstance(B, Nonterminal):
continue
beta = A[i + 1:]
#print("n: " + str(n) + " i: " + str(i) + " A: " + repr(A) + " beta: " + repr(beta))
S = FIRST(beta)
FOLLOW(B).update(everything_but_e(S))
for i in reversed(range(0, n)):
B = A[i]
if not isinstance(B, Nonterminal):
continue
# we are at the end of the list
if i == n - 1:
FOLLOW(B).update(FOLLOW(X))
continue
beta = A[i + 1:]
S = FIRST(beta)
#print(": FIRST(" + repr(beta) + ") = " + repr(S))
if Empty in S:
FOLLOW(B).update(FOLLOW(X))
else:
break
follow_len = len(FOLLOW)