What about generating the verbose accessor/single module code, and
then creating a hierarchical module space as well, all importing your
Base module, and reexporting the data types you want as well as less
verbosely named accessor functions? Of course, this will break record
update syntax, but maybe you could move to functional references
instead -- given that you're generating all the code to begin with,
autogenerating fref/lens style getter-setter pairs shouldn't be any
more work.
--Sterl
On Jul 15, 2008, at 10:43 AM, Chris Kuklewicz wrote:
Ah, a teachable moment. One of us is not entirely correct about
what GHC can do with this example. Hopefully I am wrong, but my
experiments...
Max Bolingbroke wrote:
And there is no way ghc can compile these in separate modules.
I may be being redundant here, but you may not know that GHC actually
can compile mutually recursive modules. See
http://www.haskell.org/ghc/docs/latest/html/users_guide/separate-
compilation.html#mutual-recursion
. Of course, this is not a great solution either, as creating hs-boot
files is a bit tedious, but at least the option is there.
Cheers,
Max
Consider these 3 files:
A.hs:
module A(A) where
import B(B)
data A = A B
B.hs
module B(B) where
import A(A)
data B = B A
Main.hs
> module Main where
> import A
> import B
> main = return ()
There is no way to create a "A.hs-boot" file that has all of
(1) Allows A.hs-boot to be compiled without compiling B.hs first
(2) Allows B.hs (with a {-# SOURCE #-} pragma) to be compiled
after A.hs-boot
(3) Allows A.hs to compiled after A.hs-boot with a consistent
interface
But this "Main2.hs" file works fine:
module Main where
data A = A B
data B = B A
main = return ()
But in "Main2.hs" I cannot define two record field accessors such as
> data A = A { getName :: B}
> data B = B { getName :: A}
because there cannot be two different "getName" created in the same
namespace.
There is no way GHC can put the two field accessors in different
module namespaces because their "data" types include mutual recursion.
So I can choose one of
(*) Ignore mutual recursion and make all such .proto
specifications break
(*) Autogenerate very verbose data type names and put them all in
the same module to allow mutual recursion. And then either
(**) Autogenerate even more verbose field accessor names
(**) Define no field accessors and create some poor
replacement, such as
class Field'Name a b | a ->b where
getName :: a -> b
setName :: a -> b -> a
Cheers,
Chris
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