def compute_signature(preds):
# for each predicate, compute signatures ---
# i.e. each formal parameter is assigned to one of the following categories
# sig_fw: forward local edge is passed via this parameter
# sig_bw: backward local edge is passed via this parameter
# sig_eq: "extra edge" is passed via this parameter (NOT YET IMPLEMENTED)
sig = {}
for p in preds.keys():
(params, rules) = preds[p]
sig_fw = []
sig_bw = []
sig_eq = []
for k in range(0, len(params)):
if params[k] == '':
continue
if alloc(p, k, preds) and fw_edge(p, k, preds):
sig_fw.append(k)
if points_to(p, k, preds) and bw_edge(p, k, preds):
sig_bw.append(k)
if not(k in sig_fw or k in sig_bw):
#raise InputError("Extra edges are not allowed")
sig_eq.append(k)
sig[p] = (sig_fw, sig_bw, sig_eq)
return sig
def join(preds, top_calls, emptyheap_eq, ex_quantified):
# it emptyheap_eq==[] then join sould not create some empty heap - assert in the furure
work_with_emptyheap = (not emptyheap_eq == [])
while len(top_calls) > 1:
# pick the first call for the join
call, params = top_calls.pop(0)
if emptyheap_eq == []:
empty = []
else:
empty = emptyheap_eq.pop(0)
# find a second call for a join
# maximal number of attempts is given by the number of top calls
candidate = ""
count = 0
while (candidate == "") and (count < len(top_calls)):
count = count + 1
find = 0
for i in range(len(top_calls)):
call2, params2 = top_calls[i]
if emptyheap_eq == []:
empty2 = []
else:
empty2 = emptyheap_eq[i]
p_intersect = create_intersection(params, params2)
if not (p_intersect == [] or (len(p_intersect) == 1 and "nil" in p_intersect)):
top_calls.pop(i)
if not emptyheap_eq == []:
emptyheap_eq.pop(i)
find = 1
break
if find == 0:
raise JoinFailed("Join failed")
# find the candidate variable
# - the candidate must be allocated in head of one of the calls
# - the candidate must be an existentially quantified variable
# - the candidate must be a link only between these two calls
candidate = ""
for par in p_intersect:
if (alloc(call, params.index(par), preds)):
candidate = par
if candidate == "":
# swap positions of call and call2
call_aux = call
call = call2
call2 = call_aux
params_aux = params
params = params2
params2 = params_aux
empty_aux = empty
empty = empty2
empty2 = empty_aux
for par in p_intersect:
if (alloc(call, params.index(par), preds)):
candidate = par
if candidate == "":
# still no success, push call (originally call2) back to topcalls
# swap back call2 to call
# then we will try so other item from topcall as call2
top_calls.append((call, params))
if work_with_emptyheap:
emptyheap_eq.append(empty)
(call, params, empty) = (call2, params2, empty2)
# check whether the candidate was found
if candidate == "":
raise JoinFailed(
"Join failed: impossible to join the input into a single predicate call (or bad strategy)")
if candidate == "nil":
raise JoinFailed(
"Something odd happened: nil taken as a candidate. nil existantially quantified in RootCall?")
# create a list of other parameters (different from candidate and nil) shared between the two calls
# pop the "candidate"
p_intersect.pop(p_intersect.index(candidate))
# pop all "nil" variables
while "nil" in p_intersect:
p_intersect.pop(p_intersect.index("nil"))
# the candidate is removed from the parameters after join
# if is it existentially quantified and it is not a parameter of other top level call
to_remove = candidate in ex_quantified
for (callX, paramsX) in top_calls:
if candidate in paramsX:
to_remove = False
#raise JoinFailed("Join failed: parameter %s is in more the two calls on top level"%candidate)
(call, params, empty, forbid) = do_join(candidate, call, params,
empty, call2, params2, empty2, preds, p_intersect, to_remove)
# check that variables in forbid are no more part of top calls and forbid
# is ex_quantificated
for x in forbid:
if not x in ex_quantified:
raise JoinFailed("JOIN: forbiden variable is not existentially quantified")
for (c, p) in top_calls:
if intersect_lists(p, forbid) > 0:
raise JoinFailed("JOIN: forbiden variable in other calls")
# add the newly created top call
top_calls.append((call, params))
if work_with_emptyheap:
emptyheap_eq.append(empty)
elif (not empty == []):
raise JoinFailed("JOIN: ERROR: created emptyheap from some non-empty stuff")
root_rule, root_params = top_calls[0]
if emptyheap_eq == []:
ret_empty = []
else:
ret_empty = emptyheap_eq[0]
return (root_rule, root_params, ret_empty)