Re: [Haskell-cafe] General Advice Needed ..

Yes. An approach that I have always used that has worked well for me is to keep a list of "tricks" while I am studying. Whenever I get stuck on a practice problem but eventually figure it out (either by simply thinking harder, looking it up, or asking someone for help), I try to identify the missing link that had prevented me from seeing how to do it immediately, and then write it down on my "tricks" list so that I know that I need to keep that trick in mind while I am taking the test. Cheers, Greg On Jan 14, 2010, at 8:53 AM, Ian675 wrote:

thankyou.. that made more sense to me :)

What im doing now is.. Im still working through the "Craft of Functional Programming" book but I've found a site that has solutions to some of the excercise questions. So i'm noting them down and trying to make sense of them

Is that a good approach?

Henk-Jan van Tuyl wrote:

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On Thu, 14 Jan 2010 15:38:26 +0100, Ian675 wrote:

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Pretty much yeah.. Im going through the book and things like :

Define a function rangeProduct which when given natural numbers m and n, returns the product m*(m+1)*....*(n-1)*n

I got the solution from my lecture notes but I still dont understand it..

rangeProduct :: Int -> Int -> Int rangeProduct m n | m > n = 0 | m == n = m | otherwise = m * rangeProduct (m+1) n

I'll try to give a clear explanation of this function:

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rangeProduct :: Int -> Int -> Int rangeProduct m n A function is defined with parameters m and n, both Int; the result of the function is also an Int

...

| m > n = 0

If m > n, the result is 0; the rest of the function definition will be skipped

...

| m == n = m

If m is not larger then n, evalution continues here; if m == n, the result of the function is m

...

| otherwise = m * rangeProduct (m+1) n

If previous predicates were False, this branch is evaluated ("otherwise" is always True); the function calls itself with (m+1) as first parameter

The boolean expressions in this function are called "guards"; the right hand side after the first guard that evaluates to True, will give the result of the function.

Regards, Henk-Jan van Tuyl

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