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parser.py
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45 lines (32 loc) · 1.08 KB
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#!/usr/bin/env python3
from typing import Callable, Tuple, TypeVar, Generic, Optional
T = TypeVar('T')
U = TypeVar('U')
class Parser(Generic[T]):
def __init__(self, f: Callable[[str], Optional[Tuple[T, str]]]) -> None:
self.f = f
def __call__(self, s: str) -> Optional[Tuple[T, str]]:
return self.f(s)
def __or__(self, p: 'Parser[T]') -> 'Parser[T]':
def parse(s: str) -> Optional[Tuple[T, str]]:
r1 = self(s)
if r1 is not None:
return r1
return p(s)
return Parser(parse)
def __rshift__(self, p: Callable[[T], 'Parser[U]']) -> 'Parser[U]':
def parse(s: str) -> Optional[Tuple[U, str]]:
r1 = self(s)
if r1 is None:
return None
a, s2 = r1
return p(a)(s2)
return Parser(parse)
single = Parser(lambda s: (s[0], s[1:]))
def char(c: str) -> Parser[str]:
def parse(s: str) -> Optional[Tuple[str, str]]:
if s[0] == c:
return c, s[1:]
return None
return Parser(parse)
parse_item = single