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

Subject: Re: [Haskell-cafe] General Advice Needed ..
From: Ian675
Date: Thu, 14 Jan 2010 08:53:00 -0800 PST
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 <[email protected]>  
> 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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