[Haskell-cafe] Hiding functions

[Simon Peyton-Jones]

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
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