[Haskell-cafe] General Advice Needed ..
Ian675
adam_khan_rfc at hotmail.com
Thu Jan 14 11:53:00 EST 2010
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 <adam_khan_rfc at hotmail.com>
> 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
>
>
> --
> http://Van.Tuyl.eu/
> http://members.chello.nl/hjgtuyl/tourdemonad.html
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