Proposal: Scoping rule change

[Lennart Augustsson]

An optional shadowing warning (for the paranoid) seems reasonable.


On Tue, Jul 24, 2012 at 1:45 AM, Greg Weber <greg at gregweber.info> wrote:

> sounds good. will there be a shadowing warning?
>
> On Mon, Jul 23, 2012 at 5:28 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
> > 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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> >
>
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