Re: [Haskell-beginners] Laziness, automatic memoization and arrays

On Sunday 28 August 2011, 01:03:00, Oscar Picasso wrote:

Hi,

I have a very simple question about laziness, memoization and arrays. If I have:

import Data.Array

a = listArray (1,10) $ map (\x -> (x*x)) [1..10]

main = do print c ! 4 print c ! 4 print c ! 4

Needs parentheses, print (c ! 4) Without, it parses `(print c) ! 4' since function application binds tighter than infix operators.

Can we assume that the operation 4 * 4 is evaluated only once, when first calling print c ! 4 in the main method?

Yes. Although technically an implementation is allowed to recompute the value, no serious implementation will.