On Tuesday 25 October 2005 08:36 pm, michael@schmong.org wrote:

Hi, My name is Michael. I'm new to Haskell. I'm working through The Craft of Functional Programming by Simon Thompson. I'm having problems with a few exercises from chapter 4. I will present one per post.

This one is from 4.9 Given a function f of type Int -> Int give a recursive definition of a function of type Int -> Int which on input n returns the maximum values f 0, f 1, ... , f n

I defined f as follows f 0 = 0 f 1 = 44 f 2 = 5 f 9 = 8

Most likely your problem is that f is only defined for input values 0, 1, 2 and 9. If you call f with any other value, you will end up with an error.

this works except when f n > n. In that case I get an "illegal instruction" error and hugs exits. I'm pretty sure this is a logic problem. Could someone point me in the right direction so I can think about this problem correctly. Here is my code

maxOverf :: Int -> Int maxOverf m

| f m > m = (f m) | otherwise = (maxOverf m-1)

Here you are calling f with successively decreasing values; that will run into areas where f is undefined for any value of m other than 1 or 2.

Any hints/help/flames welcome. Thanks

Try a total rather than a partial function for f. You can just add a default clause to the end, like f _ = 0 which will define f x to be 0 for all values of x except the ones already mentioned.

Am Mittwoch, 26. Oktober 2005 02:36 schrieb michael@schmong.org:

In that case I get an "illegal instruction" error and hugs exits.

This is a bug in Hugs but your code is incorrect, too. You get into infinite recursion for some argument values and I suppose, Hugs doesn't handle infinite recursions well. At least, Hugs sometimes dies with a segementation fault on Linux when it actually should cancel the computation cleanly because of a stack/heap overflow caused by infinite recursion.

[...]

Best wishes, Wolfgang