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Today's Topics:
1. Can I set Cabal conditional options for all build targets
(Dimitri DeFigueiredo)
2. Re: Finding Keith Numbers with Haskell (Rein Henrichs)
3. Re: Finding Keith Numbers with Haskell (Alexander Berntsen)
----------------------------------------------------------------------
Message: 1
Date: Tue, 11 Nov 2014 17:47:11 -0700
From: Dimitri DeFigueiredo <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Can I set Cabal conditional options for
all build targets
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252; format=flowed
Hi,
Is there a way to set a conditional in a .cabal file that applies to all
the build targets in the file?
I have many build targets and repeating the conditional for each of them
doesn't make sense.
But I get an error message when doing that.
For example, I can do this in my example.cabal file:
----
name: MyExample
build-type: Simple
-- the conditional flag I want to use
Flag production
Description: Attempts to get production env
Default: True
executable client
main-is: client.hs
if flag(production)
CPP-Options: -DPRODUCTION
executable server
main-is: server.hs
if flag(production)
CPP-Options: -DPRODUCTION
------
So I have to specify the options once per target. I get an error message
if I move the "if flag(production)" outside an "executable" block. And
the docs "seem to indicate" that's not possible.
Thanks,
Dimitri
PS. I'm using cabal "1.20.0.3"
------------------------------
Message: 2
Date: Tue, 11 Nov 2014 17:44:45 -0800
From: Rein Henrichs <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Finding Keith Numbers with Haskell
Message-ID:
<cajp6g8xh+wtbzaasm0zk7e8zwa8upcw_zmaauaswq_pn8ew...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Tue, Nov 11, 2014 at 5:26 AM, Jack Mott <[email protected]> wrote:
> I did try this approach as well, reversing the digits and adding elements
> to the head, however having to use take and letting the list build up
> larger seems to result in slightly worse performance overall.
>
The list doesn't build up. The specification for Keith Numbers requires
that we only sum the previous n numbers, where n is the length of the
decimal encoding of the given number, so we always truncate using take
before the recursive call.
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Message: 3
Date: Wed, 12 Nov 2014 10:07:03 +0100
From: Alexander Berntsen <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Finding Keith Numbers with Haskell
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
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On 11/11/14 16:17, Kim-Ee Yeoh wrote:
> On Tue, Nov 11, 2014 at 8:26 PM, Jack Mott <[email protected]>
> wrote:
>
>> Thanks, is the notation with the single quote (isKeith') a
>> convention for helper functions or does it actually change
>> something about the program?
>
>
> An unspoken coding convention.
>
> Function foo' would be read "foo-prime". E.g.of usage:
> haskell-prime is the next standard of haskell, which became moot
> because you need good vibes for diverse peoples to collaborate on
> such an undertaking, including supporting it by writing more than
> one implementation.
>
> Strictly syntax, the compiler doesn't treat it differently from
> any other name label.
>
> So yes, you could have foo-double-prime and so forth.
It's inherited from maths (like everything else). Very commonly used
for a changed/new version of something. Comes up a lot in games
programming. One banal example:
update :: World -> World
update (World p p2 b e) =
let p' = update p
p2' = update p2
b' = update b
e' = update e
in World p' p2' b' e'
where update = draw . move . react
- --
Alexander
[email protected]
https://secure.plaimi.net/~alexander
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