[Haskell-cafe] Why this cannot be compiled?

13 Jul 2009


      Hi,
  The following code failed to compiled, with error:
Attribute.hs:46:91:
    Couldn't match expected type `[t]'
           against inferred type `(a, String)'
    In the expression: (color_, rest_)
    In a case alternative: [(color_, rest_)] -> (color_, rest_)
    In the expression:
        case reads rest1 of {
          [(color_, rest_)] -> (color_, rest_)
          _ -> (Color 0 0 0, rest1) }

 43 instance Read Attribute where
 44   readsPrec _ str = [ (mkAttr attr_ color, rest) | (attr_, rest1) <- lex str
 45                                                  , (color, rest)
<- case reads rest1 of
 46
   [(color_, rest_)] -> (color_, rest_)
 47
   _ -> (Color 0 0 0, rest1) ]
 48     where mkAttr "AttrFgColor" color = AttrFgColor color
 49           mkAttr "AttrBgColor" color = AttrBgColor color
 50           mkAttr "AttrInverse" _ = AttrInverse
 51           mkAttr "AttrWeak" _ = AttrWeak
 52           mkAttr "AttrUnderline" _ = AttrUnderline
-- 
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[Haskell-cafe] Why this cannot be compiled?

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