Hi, Yes it's correct. You can check this with ghci: f :: Integer -> Maybe Integer f 5 = Nothing f x = Just x

let xs = [1..] :: [Integer] mapM f xs Nothing (it doesn't loop forever) :sprint xs xs = 1 : 2 : 3 : 4 : 5 : _ (the tail after 5 is not evaluated)

Cheers Sylvain On 22/09/2016 11:57, Dennis Raddle wrote:

I want to evaluate a function on a series of inputs:

f :: a -> Maybe b

then collect the results [b] if they are all Just, or terminate the computation immediately upon hitting Nothing.

This is exactly what mapM does in the Maybe monad, correct?

In particular I want to make sure that it will not try to evaluate anything past the first 'Nothing' result as the efficiency of my design is based on that.

D

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