Haskell - parse error on input `=' [duplicate]

问题

This question already has an answer here:

Parse error in valid code [duplicate] (1 answer)

Closed 5 years ago.

when implementing the code for the "Towers of Hanoi" problem I get the following error message:

hanoi.hs:4:24: parse error on input `='
Failed, modules loaded: none.

---

Here is the code:

hanoi 1 i j = [(i, j)]
hanoi n i j = hanoi n' i otherT ++ [(i,j)] ++ hanoi n' otherT j
    where   n' = n-1
            otherT = 1+2+3-i-j

---

Any Ideas?

回答1:

Your editor and the compiler see the tabs differently. Avoid using tabs and indent with spaces:

hanoi 1 i j = [(i, j)]
hanoi n i j = hanoi n' i otherT ++ [(i,j)] ++ hanoi n' otherT j
    where   n' = n-1
            otherT = 1+2+3-i-j

Good editors can be set up to do the right number of spaces automatically when you press tab.

来源：https://stackoverflow.com/questions/24842552/haskell-parse-error-on-input