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 eval_(text: Value) -> Value:
""" Evaluates `text` as Knight code, returning its result. """
value = Value.parse(Stream(str(text)))
if value is None:
raise ParseError('Nothing to parse.')
else:
return value.run()
