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Today's Topics:
1. Re: Are these soloutions all valid and a good use of Haskell
(Chris Linton-Ford)
2. Re: Are these soloutions all valid and a good use of Haskell
(Frerich Raabe)
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Message: 1
Date: Mon, 10 Nov 2014 10:29:29 +0000
From: Chris Linton-Ford <[email protected]>
To: "The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell" <[email protected]>
Subject: Re: [Haskell-beginners] Are these soloutions all valid and a
good use of Haskell
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Never mind - I should have Googled this:
https://www.haskell.org/haskellwiki/Haskell_programming_tips#Avoid_explicit_recursion
Chris
-----Original Message-----
From: Beginners [mailto:[email protected]] On Behalf Of Chris
Linton-Ford
Sent: Monday, November 10, 2014 10:25 AM
To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level
topics related to Haskell
Subject: Re: [Haskell-beginners] Are these soloutions all valid and a good use
of Haskell
I've seen this mentioned a couple of times - that you should avoid explicit
recursion where possible in Haskell (although I can't find the references now).
Is this to make programs easier to understand, or more compact, or is there a
performance benefit?
Chris
-----Original Message-----
From: Beginners [mailto:[email protected]] On Behalf Of Karl Voelker
Sent: Monday, November 10, 2014 10:17 AM
To: [email protected]
Subject: Re: [Haskell-beginners] Are these soloutions all valid and a good use
of Haskell
On Mon, Nov 10, 2014, at 01:50 AM, Roelof Wobben wrote:
> What do you experts think of the different ways ?
2 and 4 are quite similar, and both fine. 3 is not so good: guards provide
weaker guarantees than patterns, and head and tail are partial functions.
All three implementations have in common that they do their own recursion. It
would be a good exercise to try implementing last as a fold - in other words,
letting the standard library do the recursion for you.
-Karl
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Message: 2
Date: Mon, 10 Nov 2014 11:43:56 +0100
From: Frerich Raabe <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Are these soloutions all valid and a
good use of Haskell
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII; format=flowed
On 2014-11-10 11:16, Karl Voelker wrote:
> On Mon, Nov 10, 2014, at 01:50 AM, Roelof Wobben wrote:
>> What do you experts think of the different ways ?
>
> 2 and 4 are quite similar, and both fine. 3 is not so good: guards
> provide weaker guarantees than patterns, and head and tail are partial
> functions.
In addition to what Karl wrote, I'd like to suggest not using the semicolon
all the time -- it's not needed and just adds noise.
> All three implementations have in common that they do their own
> recursion. It would be a good exercise to try implementing last as a
> fold - in other words, letting the standard library do the recursion for
> you.
Right - I suggest trying to express the problem with the most abstract
function first, then consider using a fold, then use manual recursion. in
your particular case you could exploit that for non-empty lists, getting
the last element of a list is the same as getting the first element of
a reversed list (and there are ready-made functions for reversing a list
and getting the first element of a list).
--
Frerich Raabe - [email protected]
www.froglogic.com - Multi-Platform GUI Testing
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