Re: [Hat] Hat bug report: Ambiguous occurrence `List'

On 29-Jun-2004, Malcolm Wallace wrote:

Fergus Henderson writes:

...

This one can be reproduced with a simple one-liner, "(>>) = 42":

bash$ cat Foo.hs (>>) = 42

Hmm, but isn't (>>) indeed defined in the Prelude?

Yes.

So what is the expectation here?

This example should be allowed. hat-trans should generate a type-correct translated Haskell program from it.

Is it something to do with lazy reporting of name clashes?

Yes. The name ">>" is defined in the Prelude, but this occurrence of ">>" in Foo.hs is a definition, so it unambiguously refers to Main.>>, not Prelude.>>. The Haskell 98 report gives a similar example in section 5.5.2 "Name clashes", using "sin" rather than ">>": | For example, the following module is legal: | | module F where | | sin :: Float -> Float | sin x = (x::Float) | | f x = Prelude.sin (F.sin x) | | The local declaration for sin is legal, even though the Prelude function sin is implicitly in scope. | The references to Prelude.sin and F.sin must both be qualified to make | it unambiguous which sin is meant. However, the unqualified name sin in | the type signature in the first line of F unambiguously refers to the | local declaration for sin. -- Fergus J. Henderson | "I have always known that the pursuit Galois Connections, Inc. | of excellence is a lethal habit" Phone: +1 503 626 6616 | -- the last words of T. S. Garp.