Karl-Filip Faxen wrote
> Section 5.5.2 relates to name clashes and has an interesting example
> towards the end:
>
> module F where
>
> sin :: Float -> Float
> sin x = (x::Float)
>
> f x = Prelude.sin (F.sin x)
>
> where the type signature refers to the local "sin" rather than the imported
> although none of them is visible unqualified. These rules are quite tricky
> to understand, I think. They are also different in spirit from the rules
The Haskell report seems to be inconsistent here (once again). In the
beginning of section 5.3 it says
Imported names serve as top level declarations: they scope over the entire
body of the module but may be shadowed by local NON-TOP-LEVEL bindings.
Thus, the definition of sin in module F is invalid because another
top-level declaration of sin already exists due to the (implicit)
import of the Prelude. In order to redefine sin locally the imported
definition should be hidden and imported only qualified:
module F where
import Prelude hiding(sin)
import qualified Prelude(sin)
...
> for instance declarations in section 4.3.2 where the binding occurrences
> for the names of the methods must be qualified if the unqualified method
> name is not in scope. In the "sin" example it is allowed to resolve the
> name clash using the "extra" knowledge that it is illegal to provide type
> signatures for imported names, wheras in the case for instance declarations
> we may not use the corresponding "extra" knowledge that only methods in
> the instance'd class may be bound by the bindings.
>
> What I'm driving at is this: I propose that top level bindings shadow
> imported names and that qualified names can not be used to refer to
> declarations in the same module.
The second part is going to conflict with the revised report which relies
on the qualified names of entities in order to specify which entites exported
from module M (module M) where { ... }
> /kff
>
> who feels very relieved at having come out publicly in favour of shadowing
> imported names ;-)
Wolfgang
who prefers to forbid shadowing of imported names :-)
--
Wolfgang Lux Phone: +49-251-83-38263
Institut fuer Wirtschaftinformatik FAX: +49-251-83-38259
Universitaet Muenster Email: [EMAIL PROTECTED]
_______________________________________________
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
