[Haskell-cafe] Hiding functions

[Lyle Kopnicky]

Simon,

That makes good sense, as it's hard to read code that contains standard 
terms used in a nonstandard way.  I was just concerned that the function 
name I wanted to use was already in the Prelude!  Perhaps the Prelude 
'catch', I reasoned, could be called 'catchIO', since it is specific to 
the IO monad, allowing people to write their own 'catch'.  Or 'catch' 
could be a member of a type class, which could be overloaded for any new 
monad.

But then I realized this argument could be made for practically every 
function in the Prelude.  To dilute it with such abstraction would be a 
waste of resources.  And there are loads of synonyms... I could use 
'fling' and 'nab', 'punt' and 'snare', 'toss' and 'capture'....

Thanks for the point.

 - Lyle

Simon Peyton-Jones wrote:

>It's an explicit Haskell 98 design choice
>	http://haskell.org/onlinereport/modules.html
>
>"5.6.2  Shadowing Prelude Names
>
>The rules about the Prelude have been cast so that it is possible to use
>Prelude names for nonstandard purposes; however, every module that does
>so must have an import declaration that makes this nonstandard usage
>explicit."
>
>It's a decision one could debate, but it was an explicit choice.
>
>Simon
>
>
>
>| -----Original Message-----
>| From: haskell-cafe-bounces at haskell.org
>[mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Lyle
>| Kopnicky
>| Sent: 12 August 2004 20:23
>| To: Haskell Cafe
>| Subject: [Haskell-cafe] Hiding functions
>| 
>| Hi all,
>| 
>| I'm working on a program that uses my own brand of exceptions, and I
>| created two functions called 'throw' and 'catch'.  In order for this
>to
>| work, I hide the Prelude 'catch' in my module, called 'Cont.hs'.
>Thus:
>| 
>| module Cont where
>| import Prelude hiding (catch)
>| ...
>| throw = ...
>| catch = ...
>| 
>| This works hunky-dory until I create another file that imports Cont.
>I
>| get a conflict when I use 'catch', so I have to  hide the Prelude one
>again:
>| 
>| import Prelude hiding (catch)
>| import Cont
>| ...
>| ... throw ...
>| ... catch ...
>| 
>| So I'm a bit annoyed by this 'propagation' of hiding clauses.  Then I
>| created a new file,  that redefined throw:
>| 
>| module ResumableExceptions where
>| import Cont hiding (throw)
>| import qualified Cont (throw)
>| ...
>| throw = ... Cont.throw ...
>| 
>| Finally, I created a file using ResumableExceptions:
>| 
>| import Cont hiding (throw)
>| import ResumableExceptions
>| ...
>| ... throw ...
>| 
>| If I wanted to also use 'catch' I'd have to hide that from the Prelude
>| as well.
>| 
>| I can't use type classes to solve this problem, because the types of
>the
>| two 'throw' functions are different.
>| 
>| Perhaps I should just make up new names for these things, eh?  But
>there
>| might be code that uses 'throw' and doesn't really care which one is
>| used, and it would be nice to just modify the import line and be done
>| with it.
>| 
>| Any opinions?
>| 
>| Thanks,
>| Lyle
>| _______________________________________________
>| Haskell-Cafe mailing list
>| Haskell-Cafe at haskell.org
>| http://www.haskell.org/mailman/listinfo/haskell-cafe
>  
>