Assignment versus binding

[BartC]

On 05/10/2016 11:03, Ben Bacarisse wrote:
> Gregory Ewing <greg.ewing at canterbury.ac.nz> writes:
>
>> Steve D'Aprano wrote:
>>
>>> And (shamelessly using Python syntax) if I have a function:
>>>
>>> def spam(x):
>>>     print(x)
>>>     print(x+1)
>>>
>>> spam(time.sleep(60) or 1)
>>
>> You can't write that in Haskell, because Haskell's
>> equivalent of print() is not a function (or at least
>> it's not a function that ever returns), and neither
>> is sleep().
>
> I suppose it all depends on what "that" is exactly.  Here is the closest
> match I could come up with:
>
> import Control.Concurrent
>
> spam io = do x <- io;
>              print x;
>              print (x+1)
>
> main = spam (do threadDelay (2*10^6); return 1)
>
> It matches the Python in that the delay happens once.  To get the
> behaviour being hinted at (two delays) you need to re-bind the IO
> action:
>
> spam io = do x <- io;
>              print x;
>              x <- io;
>              print (x+1)

(I downloaded Haskell (ghc) yesterday to try this out. First problem was 
that I couldn't figure out how to do two things one after another 
(apparently you need 'do').

And when I tried to use a random number function in an expression to see 
if it was evaluated once or twice, apparently my installation doesn't 
have any form of random() (despite being a monstrous 1700MB with 20,000 
files).

Not an easy language..)

-- 
Bartc