Proposal: Scoping rule change
ekmett at gmail.com
Tue Jul 24 14:47:04 CEST 2012
+1 from me
I can't count the number of times I've had this bite me when writing ByteString-like APIs that pun names from the Prelude.
On Jul 23, 2012, at 8:28 PM, Lennart Augustsson <lennart at augustsson.net> wrote:
> 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
> 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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