Send Beginners mailing list submissions to
[email protected]
To subscribe or unsubscribe via the World Wide Web, visit
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
or, via email, send a message with subject or body 'help' to
[email protected]
You can reach the person managing the list at
[email protected]
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Beginners digest..."
Today's Topics:
1. Desugar list comprehension (mike h)
----------------------------------------------------------------------
Message: 1
Date: Wed, 2 Dec 2020 10:30:37 +0000
From: mike h <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Desugar list comprehension
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Hi,
I have
sumIs2020P1' xs = do
x <- xs
y <- xs
guard (x + y == 2020)
pure (x,y)
which has been desugared from a list comprehension
I would like to reduce this even more using >>=
So I do
sumIs2020P1'' xs = (a,b) where
(a,b):rest = filter (\(x,y) -> x + y == 2020) pairs
pairs = xs >>= \x ->
xs >>= \y ->
pure (x,y)
but really I would like the guard to be within the >>= sections but I could not
work out
how to do it!
i.e. I’m looking for something like (pseudo code)
pairs = xs >>= \x ->
xs >>= \y ->
if (x + y == 2020) then pure (x,y) else DO_NOTHING
which would then allow the filter to be removed.
Many Thanks
Mike
Dr Mike Houghton
[email protected]
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20201202/bf9fb94f/attachment-0001.html>
------------------------------
Subject: Digest Footer
_______________________________________________
Beginners mailing list
[email protected]
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
End of Beginners Digest, Vol 149, Issue 1
*****************************************
