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. optimisation of code (PICCA Frederic-Emmanuel)
2. Haskell interpretation of names produces error? (trent shipley)
3. Re: Haskell interpretation of names produces error?
(Francesco Ariis)
4. Re: optimisation of code (Oleg Nykolyn)
5. Re: optimisation of code (David McBride)
----------------------------------------------------------------------
Message: 1
Date: Fri, 21 Sep 2018 08:25:20 +0000
From: PICCA Frederic-Emmanuel
<[email protected]>
To: "The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell" <[email protected]>
Subject: [Haskell-beginners] optimisation of code
Message-ID:
<a2a20ec3b8560d408356cac2fc148e53015b32c...@sun-dag3.synchrotron-soleil.fr>
Content-Type: text/plain; charset="us-ascii"
Hello,
I would like to have your advice in order to optimize this code.
The purpose is to trigg an action 'a' if a list of files (thousands) exists.
A process copy files from one directory to another.
allFilesThere :: MonadIO m => [Path Abs File] -> m Bool
allFilesThere fs = liftIO $ allM (doesFileExist . fromAbsFile) fs
trigOnAllFiles :: MonadIO m => m r -> [Path Abs File] -> m r
trigOnAllFiles a fs = go
where
go = do
r <- allFilesThere fs
if r then a else
( do liftIO $ threadDelay 1000000
go)
It works, but it consums a lot's of resources when all the files does not
exists yet.
So I would like your advice in order to optimize it :)
thanks for your help.
Frederic
------------------------------
Message: 2
Date: Fri, 21 Sep 2018 03:26:02 -0700
From: trent shipley <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Haskell interpretation of names produces
error?
Message-ID:
<CAEFLybLneYEhpzkbH2+wi2dMUEHWJXY_0NdOXhyRgh=tc4v...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
data Prop = Const Bool
| Var Char
| Not Prop
| And Prop Prop
| If Prop Prop
| Or Prop Prop
| Yff Prop Prop -- Why do I get errors if "Yff" is replaced with
"Iff"?
| Xor Prop Prop
type Assoc k v = [(k, v)]
-- Hutton, Graham. Programming in Haskell (p. 93). Cambridge University
Press. Kindle Edition.
find :: Eq k => k -> Assoc k v -> v
find k t = head [v | (k', v) <- t, k == k']
-- Hutton, Graham. Programming in Haskell (p. 93). Cambridge University
Press. Kindle Edition.
type Subst = Assoc Char Bool
-- Hutton, 2016, Ch 8.6
eval :: Subst -> Prop -> Bool
eval _ (Const b) = b
eval s (Var x) = find x s
eval s (Not p) = not (eval s p)
eval s (And p q) = eval s p && eval s q
eval s (If p q) = eval s p <= eval s q
eval s (Or p q) = eval s p || eval s q
eval s (Yff p q) = eval s p == eval s q -- Iff produces error here
eval s (Xor p q) = eval s p /= eval s q
-- Hutton 2016 Ch 8.6
vars :: Prop -> [Char]
vars (Const _) = []
vars (Var x) = [x]
vars (Not p) = vars p
vars (And p q) = vars p ++ vars q
vars (If p q) = vars p ++ vars q
vars (Or p q) = vars p ++ vars q
vars (Yff p q) = vars p ++ vars q -- Iff produces error here
vars (Xor p q) = vars p ++ vars q
-- Hutton 2016 Ch 8.6
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20180921/b91846f9/attachment-0001.html>
------------------------------
Message: 3
Date: Fri, 21 Sep 2018 12:42:23 +0200
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Haskell interpretation of names
produces error?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hello trent,
On Fri, Sep 21, 2018 at 03:26:02AM -0700, trent shipley wrote:
> data Prop = Const Bool
> [...]
changing all the three occurrences of Yff to Iff does not produce
error.
If you change only two you will get an error, because you have a
pattern-matching against a non-existent constructor
-F
------------------------------
Message: 4
Date: Fri, 21 Sep 2018 13:46:16 +0300
From: Oleg Nykolyn <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] optimisation of code
Message-ID:
<CALqbk1Rq0pMwH6ArBSheqiCidnk8M=mo8qriyhkqygnofib...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
Current code re-checks file existence always in same order, so worst case
is - N files and only last of them does not exists.
In that case this code will re-check (N-1) files during each consecutive
retry.
This can be optimized by moving already existing files to the end of file
list(or dropping them from list completely, if files are only added but
never removed).
For this you could re-write `allFilesThere` something like:
allFilesThere fs = liftIO $ do
existing, non_existing <- partitionM (doesFileExist . fromAbsFile) fs
return (non_existing++ existing, null non_existing)
Then allFilesThere could start next iteration by checking previously
non-existing files and probably failing much faster.
On Fri, Sep 21, 2018 at 11:25 AM PICCA Frederic-Emmanuel <
[email protected]> wrote:
> Hello,
>
> I would like to have your advice in order to optimize this code.
> The purpose is to trigg an action 'a' if a list of files (thousands)
> exists.
> A process copy files from one directory to another.
>
> allFilesThere :: MonadIO m => [Path Abs File] -> m Bool
> allFilesThere fs = liftIO $ allM (doesFileExist . fromAbsFile) fs
>
> trigOnAllFiles :: MonadIO m => m r -> [Path Abs File] -> m r
> trigOnAllFiles a fs = go
> where
> go = do
> r <- allFilesThere fs
> if r then a else
> ( do liftIO $ threadDelay 1000000
> go)
>
> It works, but it consums a lot's of resources when all the files does not
> exists yet.
> So I would like your advice in order to optimize it :)
>
> thanks for your help.
>
> Frederic
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20180921/3b361ecc/attachment-0001.html>
------------------------------
Message: 5
Date: Fri, 21 Sep 2018 07:45:46 -0400
From: David McBride <[email protected]>
To: Haskell Beginners <[email protected]>
Subject: Re: [Haskell-beginners] optimisation of code
Message-ID:
<CAN+Tr41sPwqnVvLa3XAxRHgi=KoY63skus=4ctdmvof1jus...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
My first instinct is to just use anyM instead of allM
allFilesThere :: MonadIO m => [Path Abs File] -> m Bool
allFilesThere fs = liftIO $ anyM (not . doesFileExist . fromAbsFile) fs
However you'll now have the opposite problem. It will take a lot of
resources when all the files are there. But maybe that is okay for your
use case?
On Fri, Sep 21, 2018 at 4:25 AM PICCA Frederic-Emmanuel <
[email protected]> wrote:
> Hello,
>
> I would like to have your advice in order to optimize this code.
> The purpose is to trigg an action 'a' if a list of files (thousands)
> exists.
> A process copy files from one directory to another.
>
> allFilesThere :: MonadIO m => [Path Abs File] -> m Bool
> allFilesThere fs = liftIO $ allM (doesFileExist . fromAbsFile) fs
>
> trigOnAllFiles :: MonadIO m => m r -> [Path Abs File] -> m r
> trigOnAllFiles a fs = go
> where
> go = do
> r <- allFilesThere fs
> if r then a else
> ( do liftIO $ threadDelay 1000000
> go)
>
> It works, but it consums a lot's of resources when all the files does not
> exists yet.
> So I would like your advice in order to optimize it :)
>
> thanks for your help.
>
> Frederic
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20180921/4fc93550/attachment.html>
------------------------------
Subject: Digest Footer
_______________________________________________
Beginners mailing list
[email protected]
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
End of Beginners Digest, Vol 123, Issue 9
*****************************************
