If Lennart's suggestion is combined with GHC's lazy checking for name clashes (i.e., only check if you ever look a name up in a particular scope), it would also work in your example. Manuel "Sittampalam, Ganesh" <ganesh.sittampalam@credit-suisse.com>:
If you’re using unqualified and unrestricted imports, there’s still the risk that another module will export something you care about, e.g.
module M where import I -- currently exports foo import J -- might be changed in future to export foo
… foo …
So I think you need to use import lists or qualified anyway to avoid any risk of future name clashes – given that, does this change buy much?
From: haskell-prime-bounces@haskell.org [mailto:haskell-prime-bounces@haskell.org] On Behalf Of Lennart Augustsson Sent: 24 July 2012 02:29 To: Haskell Prime Subject: Proposal: Scoping rule change
It's not often that one gets the chance to change something as fundamental as the scoping rules of a language. Nevertheless, I would like to propose a change to Haskell's scoping rules.
The change is quite simple. As it is, top level entities in a module are in the same scope as all imported entities. I suggest that this is changed to that the entities from the module are in an inner scope and do not clash with imported identifiers.
Why? Consider the following snippet
module M where import I foo = True
Assume this compiles. Now change the module I so it exports something called foo. After this change the module M no longer compiles since (under the current scoping rules) the imported foo clashes with the foo in M.
Pros: Module compilation becomes more robust under library changes. Fewer imports with hiding are necessary.
Cons: There's the chance that you happen to define a module identifier with the same name as something imported. This will typically lead to a type error, but there is a remote chance it could have the same type.
Implementation status: The Mu compiler has used the scoping rule for several years now and it works very well in practice.
-- Lennart
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