Haskell - parse error on input `='

Question

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?

Seems you have mixed tabs and spaces. – max taldykin Jul 19 '14 at 16:38 — max taldykin, Jul 19 '14 at 16:38

score 1 · Answer 1 · answered Jul 19 '14 at 16:40

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.

1 Answers1