On Fri, Jul 19, 2013 at 3:23 PM, Matt Ford <matt@dancingfrog.co.uk> wrote:
I started by putting brackets in

([1,2] >>= \n -> [3,4]) >>= \m -> return (n,m)

This immediately fails when evaluated: I expect it's something to do
with the n value now not being seen by the final return.

You're bracketing from the wrong end, which your intuition about n's visibility hints at.  Try this as your first set of parens:

 [1,2] >>= (\n -> [3,4] >>= \m -> return (n,m))

--Rogan
 

It seems to me that the return function is doing something more than
it's definition (return x = [x]).

If ignore the error introduced by the brackets I have and continue to
simplify I get.

[3,4,3,4] >>= \m -> return (n,m)

Now this obviously won't work as there is no 'n' value.  So what's
happening here? Return seems to be doing way more work than lifting the
result to a list, how does Haskell know to do this?  Why's it not in the
function definition?  Are lists somehow a special case?

Any pointers appreciated.

Cheers,

--
Matt

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe