def parse(stream: Stream) -> Union[None, Function]:
"""
Parses a `Function` from the stream, returning `None` if the
stream didn't start with a function character.
This will both parse the function name, and its arguments. If not
all the arguments could be parsed, a `ParseError` is raised.
"""
name = stream.peek()
if name not in _FUNCS:
return None
func = _FUNCS[name]
stream.matches(Function.REGEX)
args = []
for arg in range(func.__code__.co_argcount):
value = Value.parse(stream)
if value is None:
raise ParseError(f'Missing argument {arg} for function {name}')
args.append(value)
return Function(func, name, args)
def parse(cls, stream: Stream) -> Union[None, Number]:
"""
Parses a Number out from the stream.
This returns `None` if the stream doesn't start with a digit.
"""
if match := stream.matches(Number.REGEX):
return cls(int(match))
def parse(cls, stream: Stream) -> Union[None, Identifier]: """ Parses an Identifier out from the stream. This returns `None` if the stream doesn't start with a lowercase letter, or an underscore. """ if match := stream.matches(Identifier.REGEX): return cls(match)
def parse(cls, stream: Stream) -> Union[None, String]:
"""
Parses a `String` from the `stream`, returning `None` if the
nothing can be parsed.
If a starting quote is matched and no ending quote is, then a
`ParseError` will be raised.
"""
quote = stream.matches(String.BEGIN_REGEX)
if not quote:
return None
regex = String.SINGLE_REGEX if quote == "'" else String.DOUBLE_REGEX
body = stream.matches(regex, 1)
if body is None:
raise ParseError(f'unterminated string encountered: {stream}')
else:
return String(body)
def parse(cls, stream: Stream) -> Union[None, Boolean]:
""" Parses a `Boolean` if the stream starts with `T` or `F`. """
if match := stream.matches(Boolean.REGEX, 1):
return cls(match == 'T')
def parse(cls, stream: Stream) -> Union[None, Boolean]:
""" Attempts to parse a `Boolean """
if match := stream.matches(r'([TF])[A-Z]*', 1):
return cls(match == 'T')
def parse(cls, stream: Stream) -> Union[None, Null]:
""" Parses `Null` if the stream starts with `N`. """
if match := stream.matches(r'N[A-Z]*'):
return cls()
def parse(cls, stream: Stream) -> Union[None, Null]:
""" Parses `Null` if the stream starts with `N`. """
if stream.matches(Null.REGEX):
return cls()
else:
return None