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Today's Topics:
1. Re: best way to code this~~ ([email protected])
2. Command line interface programming (Dananji Liyanage)
----------------------------------------------------------------------
Message: 1
Date: Sun, 31 May 2015 08:02:29 -0700
From: <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] best way to code this~~
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII
On Sun, 31 May 2015 05:17:10 +0000
Alex Hammel <[email protected]> wrote:
> f as alist = [ b | (a, b) <- alist, a `elem` as ]
>
> perhaps?
perhaps. i have no idea how that works. but don't spoil it for me though, i'm
going to go of and study it :-)
@Chaddai . this is for very small lists, so optimization in the form of sorting
and binary lookup is definitely not worth the effort.
Here's what I finally wrote. partitionMaybe is a modified version of partition
from the List library.
unsure what the ~(ts, fs) syntax is though, removing the `~` doesn't seem to
matter.
this seems fairly clean. i noticed that partition simply uses foldr. it looks
like select is just a helper so that partition isn't cluttered. i'm unsure why
select was broken out as a separate function instead of just being in a where
clause. possibly to be able to assign it a an explicit type signature ? more
likely it has something to do with the fact that in the library partition is
declared inline.
extract :: [(String,b)] -> [String] -> ([b], [String])
extract alist l =
let inList s = lookup (uppercase s) alist
(l1, l2) = partitionMaybe inList l
in
(l1, l2)
partitionMaybe :: (a -> Maybe b) -> [a] -> ([b],[a])
partitionMaybe p xs = foldr (select p) ([],[]) xs
select :: (a -> Maybe b) -> a -> ([b], [a]) -> ([b], [a])
select p x ~(ts,fs) | isJust y = ((fromJust y):ts,fs)
| otherwise = (ts, x:fs)
where
y = p x
------------------------------
Message: 2
Date: Mon, 1 Jun 2015 15:41:54 +0530
From: Dananji Liyanage <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Command line interface programming
Message-ID:
<CAAPsY8z063srqTJCn2gV6mp9a=i8ww4pTH-7Cp=qh14a1ro...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi All,
I'm in the process of learning Haskell, and I need to write a command line
interface program which can interact with the user.
Right now, I have a sample program written using 'System.Console.Haskeline'
package.
Can someone please give me some additional material, which I can read on
with respect to this?
Thanks in advance!
--
Regards,
Dananji Liyanage
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