infelicity in module imports

Simon Peyton-Jones [email protected]
Thu, 12 Jul 2001 01:24:51 -0700


| I have often tried, but never succeeded, to understand what
| the report says and at the same time unify it with what the=20
| particular compiler I was using actually implemented.

Could I ask you to try one more time, with the current draft report?
available at
	http://research.microsoft.com/~simonpj/haskell98-revised

I have tried hard to make it easy to understand.  I am sure the result
is not perfect.  If it is not fairly easy to answer your questions below
by reading the text, then I would like to improve the text.  Can you
suggest ways in which it could be made clearer?

I've filled in the answers to each of your examples.

Simon


| Namely what happens in each of the following cases:
| Where A is a module exporting the names x, y, p, q, v, w.

|   import A
x, y, p, q, v, w
A.x, A.y, A.p, A.q, A.v, A.w

|   import A()
nothing is imported, except instance declarations

|   import A(x,y)
x, y, A.x, A.y

|   import qualified A
A.x, A.y, A.p, A.q, A.v, A.w

|   import qualified A()
nothing is imported, except instance declarations

|   import qualified A(x,y)
A.x A,y

|   import A hiding ()
same as import A

|   import A() hiding ()
syntactically illegal

|   import A(x,y) hiding ()
syntactically illegal

|   import A hiding (p,q)
x, y,  v, w
A.x, A.y,  A.v, A.w

|   import A() hiding (p,q)
syntactically illegal

|   import A(x,y) hiding (p,q)
syntactically illegal

|   import qualified A hiding ()
same as import qualified A

|   import qualified A() hiding ()
syntactically illegal

|   import qualified A(x,y) hiding ()
syntactically illegal

|   import qualified A hiding (p,q)
A.x, A.y,  A.v, A.w

|   import qualified A() hiding (p,q)
syntactically illegal

|   import qualified A(x,y) hiding (p,q)
syntactically illegal
|=20
| Honestly, in some of these case I do not understand if 1) it
| is legal syntax, and if so, 2) what happens, and, if not so,
| 3) why not.