haskell - Parse error in valid code -

haskell - Parse error in valid code -

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why shouldn't mix tabs , spaces? 1 reply

can see error? can't! ghc points at:

err == err = true

but line ok (maybe).

data stone = black | white | none | err instance eq stone black == black = true white == white = true none == none = true err == err = true _ == _ = false instance show stone show black = "b " show white = "w " show err = "e " show none = "n "

error message: main.hs:9:20: parse error on input `='

it's classic tabs versus spaces issue. replace tabs spaces:

data stone = black | white | none | err instance eq stone black == black = true white == white = true none == none = true err == err = true _ == _ = false instance show stone show black = "b " show white = "w " show err = "e " show none = "n "

compiles fine.

the compiler , editor see tabs differently, utilize spaces exclusively avoid problem.

good editors can set utilize spaces indent same amount tab would, autoindent subsequent lines match, , utilize backspace if backtab.

haskell