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

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:

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

...

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:

...

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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