[Haskell-beginners] Could not get parser ready

[Marcus Manning]

Hello,

I follow the instructions of script [1] in order to set up a parser 
functionality. But I' get into problems at page 202 with the code:

p :: Parser (Char,Char)
p = do
              x ← item
              item
              y ← item
              return (x,y)


ghci and ghc throw errors:
Prelude> let p:: Parser (Char,Char); p = do {x <- item; item; y <- item; 
return (x,y)}

<interactive>:10:65: error:
     • Couldn't match type ‘[(Char, String)]’ with ‘Char’
       Expected type: String -> [((Char, Char), String)]
         Actual type: Parser ([(Char, String)], [(Char, String)])
     • In a stmt of a 'do' block: return (x, y)
       In the expression:
         do x <- item
            item
            y <- item
            return (x, y)
       In an equation for ‘p’:
           p = do x <- item
                  item
                  y <- item
                  ....
Did the semantics of do expr changed?

[1] 
https://userpages.uni-koblenz.de/~laemmel/paradigms1011/resources/pdf/haskell.pdf

Cheers,

iconfly.