def _selection_share_common(sel: Antlr4Selection, start_index):
assert start_index == 0 or start_index == -1
assert isinstance(sel, Antlr4Selection), sel.__class__
# find options which starting with the same element
with_item = {i: set([
i,
])
for i in range(len(sel))}
for i0, p_opt in enumerate(sel):
for i1, opt in enumerate(islice(sel, i0 + 1, None)):
if p_opt and opt and p_opt[start_index] == opt[start_index]:
prefix_cls = with_item[i0]
prefix_cls.update(with_item[i0 + i1 + 1])
with_item[i0 + i1 + 1] = prefix_cls
resolved = set()
new_options = []
changed = False
for i, _prefix_eq_cls in sorted(with_item.items()):
if i in resolved:
continue
if len(_prefix_eq_cls) == 1:
# keep option as it is
new_opt = sel[i]
else:
changed = True
# extraction of shared prefix
eq_cls = list(sorted(_prefix_eq_cls))
extracted_item = sel[i][start_index]
if start_index == 0:
new_opt = Antlr4Sequence([
extracted_item,
Antlr4Selection(
[Antlr4Sequence(sel[i0][1:]) for i0 in eq_cls])
])
else:
assert start_index == -1
new_opt = Antlr4Sequence([
Antlr4Selection(
[Antlr4Sequence(sel[i0][:-1]) for i0 in eq_cls]),
extracted_item
])
resolved.update(eq_cls)
new_options.append(new_opt)
if len(new_options) == 1:
return new_options[0], changed
else:
sel.clear()
sel.extend(new_options)
return sel, changed
def _selection_reduce_optional(o: Antlr4Selection):
"""
a? | b? -> (a | b)?
"""
assert isinstance(o, Antlr4Selection)
non_optional_items = []
for c in o:
if isinstance(c, Antlr4Sequence):
if len(c) != 1:
return o, False
c = c[0]
if not isinstance(c, Antlr4Option):
return o, False
non_optional_items.append(c.body)
o.clear()
o.extend(non_optional_items)
return Antlr4Sequence([
Antlr4Option(o),
]), True