Re: [Haskell-beginners] Question about example in 'using do notation with Writer' section of LYH

27 Jan 2017

      On 26/01/2017 16:02, David McBride wrote:
...
Nothing happens to them.  They are still in there.  Whereas logNumber
always returns the number you give it, multiWithLog always returns 15
and appends two strings into its state ("got number 3 and 5").
You can return whatever value you want from a Monad.  In this case
he's doing a * b, but you could do 2 * b, Just (a + b) or anything
else.  As an example, here I return a tuple instead.
multWithLogTuple :: Writer [String] (Int,Int,Int)
multWithLogTuple = do
    a <- logNumber 3
    b <- logNumber 5
    return (a,b,2*b)
So return (a*b) still creates Writer [String] Int?

I thought the [String] parts of 'a' and 'b' ought to be in the result 
but I see it needn't.

- Olumide