[Haskell-cafe] strange error message

[Semen Trygubenko / Семен Тригубенко]

Dear Haskell-Cafe,

Every now and then I get error messages when compiling Haskell code :).
Sometimes of the sort:

test.hs:10:15:
    Couldn't match type `[[a2]]' with `Int'
    Expected type: Int -> Int
      Actual type: [[a2]] -> Int
    The function `length . head' is applied to one argument,
    but its type `[[a2]] -> Int' has only one
    In the first argument of `(==)', namely `(length . head) r'
    In the expression: (length . head) r == 0

Is the middle part of the error message

(The function `length . head' is applied to one argument,
but its type `[[a2]] -> Int' has only one)

expected to be confusing like that sometimes?

The line in question, FWIW, is

Right r -> if (length . head) r == 0

It appears as one of the two entries in a case statement, pattern matching on Right constructor.

Many thanks,
S.



--
Семен Тригубенко http://trygub.com
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