def try_read_rule(ctx: ReadContext) -> Optional[RuleExp]:
loc0 = ctx.source.location
name = try_read_name(ctx)
if name is None:
return None
read_void(ctx)
if ctx.source.pull(soft_assignment_mark):
soft = True
elif ctx.source.pull(hard_assignment_mark):
soft = False
else:
raise ctx.source.error_expected_symbols(soft_assignment_mark,
hard_assignment_mark)
read_void(ctx)
expression = read_expression(ctx)
result = RuleExp(name, expression, soft)
result.area = loc0.area(ctx.source.location)
return result
def read_expression(ctx: ReadContext) -> Expression:
loc0 = ctx.source.location
alt_seq: List[List[Expression]] = [[]]
while True:
expression = try_read_expression_item(ctx)
if expression is None:
break
alt_seq[-1].append(expression)
read_void(ctx)
if ctx.source.pull(alternation_mark):
read_void(ctx)
if len(alt_seq[-1]) == 0:
raise ctx.error('Expected expression.')
alt_seq.append([])
if len(alt_seq) == 0:
raise ctx.error('Expected expression.')
return generate_alt_seq_expression(alt_seq, ctx, loc0)
def parse_source(source: Source) -> List[Element]:
ctx = ReadContext(source)
elements = []
while True:
read_void(ctx)
rule = try_read_rule(ctx)
if rule is None:
break
elements.append(rule)
return elements
def try_read_optional(ctx: ReadContext) -> Optional[OptionalExp]:
loc0 = ctx.source.location
if not ctx.source.pull(optional_begin_mark):
return None
read_void(ctx)
expression = read_expression(ctx)
if not ctx.source.pull(optional_end_mark):
raise ctx.source.error_expected_symbols(optional_end_mark)
result = OptionalExp(expression)
result.area = loc0.area(ctx.source.location)
return result
def try_read_group(ctx: ReadContext) -> Optional[Expression]:
loc0 = ctx.source.location
if not ctx.source.pull(group_begin_mark):
return None
read_void(ctx)
expression = read_expression(ctx)
if not ctx.source.pull(group_end_mark):
raise ctx.source.error_expected_symbols(group_end_mark)
# override area
expression.area = loc0.area(ctx.source.location)
return expression
def try_read_reference(ctx: ReadContext) -> Optional[ReferenceExp]:
loc0 = ctx.source.location
name = try_read_name(ctx)
if name is None:
return None
read_void(ctx)
if (ctx.source.pull(soft_assignment_mark)
or ctx.source.pull(hard_assignment_mark)):
ctx.source.position = loc0.position
return None
result = ReferenceExp(name)
result.area = loc0.area(ctx.source.location)
return result
def try_read_negation(ctx: ReadContext) -> Optional[NegationExp]:
loc0 = ctx.source.location
if not ctx.source.pull(negation_mark):
return None
if read_void(ctx) > 0:
raise ctx.source.error_expected_symbols(negation_mark)
expression = try_read_expression_item(ctx)
if expression is None:
raise ctx.error('Expected expression.')
result = NegationExp(expression)
result.area = loc0.area(ctx.source.location)
return result
def try_read_repetition(ctx: ReadContext) -> Optional[RepetitionExp]:
loc0 = ctx.source.location
if not ctx.source.pull(repetition_begin_mark):
return None
read_void(ctx)
min_count = try_read_integer(ctx)
max_count = None
if min_count is not None:
read_void(ctx)
if ctx.source.pull(repetition_range_mark):
read_void(ctx)
max_count = try_read_integer(ctx)
if max_count is None:
raise ctx.error('Expected max_count.')
read_void(ctx)
elif ctx.source.pull(repetition_count_mark):
max_count = min_count
read_void(ctx)
expression = read_expression(ctx)
if ctx.source.pull(repetition_separator_mark):
read_void(ctx)
separator = read_expression(ctx)
else:
separator = None
if not ctx.source.pull(repetition_end_mark):
raise ctx.source.error_expected_symbols(repetition_end_mark)
result = RepetitionExp(expression, separator, min_count, max_count)
result.area = loc0.area(ctx.source.location)
return result