Sorry to bother again. I just cannot figure out how it could compile.
I got compile errors.
Can someone point out what is right code to use a do notion to make a
Parser works.
Thanks in advance.
--------------------------------------------------------------------------------------------
newtype Parser a = P { parse :: (String -> [(a,String)]) }
instance Monad Parser where
return v = P (\s -> [(v,s)])
p >>= f = P (\s -> case parse p s of
[] -> []
[(v,str)] -> parse (f v) str)
fail _ = P (\_ -> [])
item :: Parser Char
item = \inp -> case inp of
[] -> []
(x:xs) -> [(x,xs)]
p :: Parser (Char,Char)
p = do x <- item
item
y <- item
return (x,y)
---------------------------------------------------------------------------------
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