On Wed, Jul 25, 2007 at 11:27:59AM -0700, Alexteslin wrote:
Hi,
I am going through examples from the textbook and trying them out but some don't work. For example:
addNum :: Int -> (Int -> Int) addNum n = addN where addN m = n+m
This error message i am getting:
ERROR - Cannot find "show" function for: *** Expression : addNum 4 *** Of type : Int -> Int
Now, the type of show is a->String, but i need some kind of function to print the function as a result. I tried some input output functions but i don't think that is the right way to follow.
Can anyone suggest me where to look?
You can't print function values because there is no reasonable way to do it; printing the definition would break useful equations like 2 + 2 = 4 (since show (\_ -> 2 + 2) == "\_ -> 2 + 2" /= "\_ -> 4" == show (\_ -> 4); printing the table of values would take forever for a big type like Int (at least a billion constructors, many more on some systems), etc. You can print applications of functions, however; (addNum 4) 10 ==> 14 (addNum 4) 20 ==> 24 etc. Stefan