[Haskell-cafe] RE: Packages and modules

Simon Peyton-Jones simonpj at microsoft.com
Thu Jul 6 11:51:05 EDT 2006

| 1) Qualified names:
|   import A.B.C( T1 ) from "foo"
|   import A.B.C( T2 ) from "bar"
|   type S = A.B.C.T1 -> A.B.C.T2
| I'd suggest that the above should give a compiler error that A.B.C is
| ambiguous (as a qualifier), rather than allowing T1 to disambiguate
| because otherwise it allows people to write code that could be very
hard to
| understand ie within the code, every occurrence of A.B.C as a
| should refer to the same module. (Otherwise the thing qualified
| the qualifier that's qualifying it...)

But that's inconsistent with Haskell 98.  In H98 you can say
	import M( T1 ) as Q
	import N( T2 ) as Q
	type S = Q.T1 -> Q.T2
and it'll work just fine.  You may think it should not work, but that's
water under the bridge.  We should be consistent here.

| In my spec, if you omit the package name you get an "old-style" import
| the shared namespace, and if you supply a package name you get a
| import that only searches in the specified package:
|     import A.B.C -- search home + exposed as is done at the moment
|     import "" A.B.C -- search home package only
|     import "pkg" A.B.C -- search "pkg" only

That's exactly what our spec says too.  (Good news, again.)  Only maybe
not explicitly enough!  See the section "Is the from<package>
compulsory".   Perhaps you could improve the wording to make it more

Indeed, if we've converged, would you like to fold into our draft
whatever you think is useful from yours?


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