[Haskell-cafe] [Maybe Int] sans Nothings

michael rice nowgate at yahoo.com
Mon May 23 19:52:21 CEST 2011

Thanks, all.
Earlier, I was going to ask how to break out of a sequence op prematurely, i.e., you give it some replication number but want to break early if you get an end-flag value. While I was composing the post I thought of using Maybe for the good values and Nothing for the end value. Ergo, losing the Nothings at the end.
I was passing a map and an empty list into some state, but since the map doesn't change once it's created I moved it into a Reader. I was using the list to collect the elements but thought I can get that functionality automatically using sequence. 
So, one thing leads to another. It's interesting how ideas begin bubbling up after one absorbs some critical mass of Haskell.
--- On Mon, 5/23/11, Malcolm Wallace <malcolm.wallace at me.com> wrote:

From: Malcolm Wallace <malcolm.wallace at me.com>
Subject: Re: [Haskell-cafe] [Maybe Int] sans Nothings
To: "haskell-cafe Cafe" <haskell-cafe at haskell.org>
Date: Monday, May 23, 2011, 12:35 PM

On 23 May 2011, at 17:20, michael rice wrote:

> What's the best way to end up with a list composed of only the Just values,
> no Nothings?


    [ x      | Just x <- originals ]

It also occurs to me that perhaps you still want the Just constructors.

    [ Just x | Just x <- originals ]
    [ x      | x@(Just _) <- originals ]

Haskell-Cafe mailing list
Haskell-Cafe at haskell.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20110523/36f23154/attachment.htm>

More information about the Haskell-Cafe mailing list