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