[Haskell-cafe] Printing the function result
alexteslin at yahoo.co.uk
Wed Jul 25 15:50:13 EDT 2007
Thank you guys, i didn't understand the concept of the chapter.
Brent Yorgey wrote:
> On 7/25/07, Alexteslin <alexteslin at yahoo.co.uk> wrote:
>> I am going through examples from the textbook and trying them out but
>> don't work.
>> For example:
>> addNum :: Int -> (Int -> Int)
>> addNum n = addN
>> addN m = n+m
>> This error message i am getting:
>> ERROR - Cannot find "show" function for:
>> *** Expression : addNum 4
>> *** Of type : Int -> Int
> Printing functions is in general not possible, since given a function f
> there is no way to "get at" its implementation.* Functions are like black
> boxes. The only way to observe a function is to observe its effect on
> various inputs. So you can try (addNum 4) 6, (addNum 4) 0, and so on to
> see what the function (addNum 4) does to various Int values.
> *(If there were it would lead to all sorts of fun
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