Haskell: Error when passing a non-empty list to a function
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I have written this small function to retrieve the tail of a list:

    let getTail l = if length l > 0 then tail l else "empty list"
Passing `[]`to `getTail` returns `empty list` but passing `[1,2,3]` gives the following error:

    <interactive>:1:14:
    No instance for (Num Char)
      arising from the literal `3'
    Possible fix: add an instance declaration for (Num Char)
    In the expression: 3
    In the first argument of `getTail', namely `[1, 2, 3]'
    In the expression: getTail [1, 2, 3]
I can't understand what that error means. What is the problem? Using GHCi 7.0.4