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Today's Topics:
1. general comments requested (Michael Mossey)
2. Re: general comments requested (Stephen Tetley)
3. Template Haskell confusion (Alex Rozenshteyn)
4. Re: general comments requested (Michael Mossey)
5. Re: general comments requested (Heinrich Apfelmus)
----------------------------------------------------------------------
Message: 1
Date: Sat, 17 Jul 2010 12:35:42 -0700
From: Michael Mossey <[email protected]>
Subject: [Haskell-beginners] general comments requested
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I'm wondering if I could get really general comments on my program...
like notes about language features I'm failing to take advantage of.
This is part of a program to convert MusicXML to a simpler
representation which I then manipulate. Most of the data is defined in
MusDoc.Data:
<http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27679#a27679>
and the functions are defined in MusDoc.FromXml:
<http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27678#a27678>
A module called XmlAccess can access various interesting parts of the
MusicXML document in a way that lets me ignore most of its complexity:
<http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27680#a27680>
MusicXML Haskell module can be found here:
<http://hackage.haskell.org/package/musicxml>
Thanks,
Mike
------------------------------
Message: 2
Date: Sat, 17 Jul 2010 21:29:36 +0100
From: Stephen Tetley <[email protected]>
Subject: Re: [Haskell-beginners] general comments requested
To: Michael Mossey <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
Hi Michael
It looks fine - with one big exception.
Tracking down /undefined/ can be quite tedious, there is no indication
at run time which particular undefined signalled the exit - I'd
recommend you always throw an error with an identifiable string.
Also, I wonder if the the MusicXML library on Hackage was
auto-generated at least in part?
It would be nicer to work with if it used constructors and
field-labels more, rather than long tuples; though there isn't much
you can do about that.
Best wishes
Stephen
------------------------------
Message: 3
Date: Sat, 17 Jul 2010 18:45:17 -0400
From: Alex Rozenshteyn <[email protected]>
Subject: [Haskell-beginners] Template Haskell confusion
To: beginners <[email protected]>
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="utf-8"
I'm trying to learn Template Haskell.
I decided to try to write a mapTup function which takes function and a tuple
(e.g. mapTup id (1,"hi",'a') ) and, well, applies the function to each cell.
The closest I've gotten so far is this:
> {-# LANGUAGE TemplateHaskell #-}
> module MapTup
> where
> import Language.Haskell.TH
> import Control.Monad
>
> mapTup fun tup = do
> funE <- runQ $ [| $fun |]
> TupE tupContents <- runQ $ [| $tup |]
> return $ TupE $ map (AppE funE) tupContents
The problem is that I can't figure out how to get the representation of the
values bound to fun and tup.
Sorry if I'm wording this badly. My head hurts from meta-programming ;)
--
Alex R
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Message: 4
Date: Sat, 17 Jul 2010 15:54:58 -0700
From: Michael Mossey <[email protected]>
Subject: Re: [Haskell-beginners] general comments requested
To: haskellbeginners <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Thanks, Stephen. I didn't realize I had left all those undefined's in
there. I don't know of the origin of the MusicXML package. One nice
thing is that reading the source for it, and looking at what fields go
in the tuples, give a clue about the valid combinations of elements in
MusicXML. Otherwise, I had at my disposal only some MusicXML tutorials,
which don't go into depth. I supposed I could look at the XMD file or
whatever that's called (the document that defines MusicXML) but I am not
currently familiar with how to read those.
Mike
Stephen Tetley wrote:
> Hi Michael
>
> It looks fine - with one big exception.
>
> Tracking down /undefined/ can be quite tedious, there is no indication
> at run time which particular undefined signalled the exit - I'd
> recommend you always throw an error with an identifiable string.
>
> Also, I wonder if the the MusicXML library on Hackage was
> auto-generated at least in part?
>
> It would be nicer to work with if it used constructors and
> field-labels more, rather than long tuples; though there isn't much
> you can do about that.
>
> Best wishes
>
> Stephen
------------------------------
Message: 5
Date: Sun, 18 Jul 2010 14:31:34 +0200
From: Heinrich Apfelmus <[email protected]>
Subject: [Haskell-beginners] Re: general comments requested
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
Michael Mossey wrote:
> I'm wondering if I could get really general comments on my program...
> like notes about language features I'm failing to take advantage of.
>
> This is part of a program to convert MusicXML to a simpler
> representation which I then manipulate. Most of the data is defined in
> MusDoc.Data:
>
> <http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27679#a27679>
>
> and the functions are defined in MusDoc.FromXml:
>
> <http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27678#a27678>
>
> A module called XmlAccess can access various interesting parts of the
> MusicXML document in a way that lets me ignore most of its complexity:
>
> <http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27680#a27680>
I'm not familiar enough with the problem domain to say anything about
the large scale organization of your code.
But on a per-function scale, you have a few helper functions that are
best expressed with list comprehension and combinators like fold or
listToMaybe instead of general recursion. For instance, I recommend to
write
-- in module MusDoc.XmlAccess
headerScoreParts = ...
where
remainder = [part | Part_List_2 scorePart <- pl_s]
-- in module MusDoc.FromXml
xScorePart = ...
where ...
lookupMidiInstr scInstrId =
listToMaybe . filter ((scInstrId==) . A.midiInstrumentId)
In a sense, the Haskell Prelude and standard libraries come with a
superb "domain specific language for manipulating (some) lists" which is
much easier to understand and visualize than general recursion. :)
Concerning the MusicXML package itself, I think the use of 7-tuples in
the MusicXML package for data types like Score_Header is creepy. I do
admit that it has some interesting, yet ghastly appeal due to its
regularity, but frankly, I think this is bad design. For instance,
consider the following randomly chosen example
data Orientation_ = Orientation_1 | Orientation_2
deriving (Eq, Show)
read_Orientation_ :: Data.Char.String -> Result Orientation_
read_Orientation_ "over" = return Orientation_1
read_Orientation_ "under" = return Orientation_2
I am rather dissatisfied that the constructors are named Orientation_1
and Orientation_2 instead of Over and Under , and that
read_Orientation is not a member of a type class or thelike.
I can only hope that this code was generated automatically ...
Regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
------------------------------
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