MonoLocalBinds and hoopl

[Iavor Diatchki]

Hello,
Another design-pattern which sometimes works pretty well is to
encapsulate commonly used polymorphic types in ordinary data-types
(i.e., use the rank-2 style). Then, the data-type constructors provide
a quick way to---essentially---write a type signature. It seems that
this should work well in combination with mono-bindings.
Unfortunately,  I am not sure that this would work for HOOPL (I
haven't looked at the code in detail), so apologies if this is a
red-herring.
-Iavor

On Fri, Dec 10, 2010 at 4:52 AM, Simon Peyton-Jones
<simonpj at microsoft.com> wrote:
> Yes, argument to higher rank functions are probably the top reason why MonoLocalBinds is a nuisance.
>
> As of now I think the best thing is to do (1), but define type synonyms that abbreviate the oft-repeated signatures. That should make the signatures much onerous.
>
> Simon
>
> | -----Original Message-----
> | From: Edward Z. Yang [mailto:ezyang at MIT.EDU]
> | Sent: 09 December 2010 15:28
> | To: glasgow-haskell-users; Simon Peyton-Jones
> | Subject: MonoLocalBinds and hoopl
> |
> | Hello all,
> |
> | Here's an experience report for porting hoopl to manage MonoLocalBinds.  The
> | Compiler.Hoop.XUtil module has a rather interesting (but probably common)
> | style of code
> | writing, along the lines of this:
> |
> | fbnf3 (ff, fm, fl) block = unFF3 $ scottFoldBlock (ScottBlock f m l cat)
> | block
> |     where f n = FF3 $ ff n
> |           m n = FF3 $ fm n
> |           l n = FF3 $ fl n
> |           FF3 f `cat` FF3 f' = FF3 $ f' . f
> |
> | f, m, l and cat are polymorphic functions that are only used once in the
> | main expression, and are floated outside to improve readability.  However,
> | when
> | MonoLocalBinds is turned on, these all become monomorphic and the definitions
> | fail.  In contrast, this (uglier) version typechecks:
> |
> | fbnf3 (ff, fm, fl) block = unFF3 $ scottFoldBlock (ScottBlock (FF3 . ff) (FF3
> | . fm) (FF3 . fl) (\(FF3 f) (FF3 f') -> FF3 $ f' . f)) block
> |
> | One suggestion that I had was that we should generalize local bindings that
> | are only used once, but Marlow pointed out that this would make the
> | typechecker
> | more complex and I probably would agree.
> |
> | As a userspace developer, I have two options:
> |
> |     1. Bite the bullet and put in the polymorphic type signatures (which
> |        can be quite hefty)
> |     2. Inline the definitions
> |     3. Move the polymorphic functions into the global namespace
> |
> | (3) and (2) are not so nice because it breaks the nice symmetry between these
> | definitions, which always define f, m, l for the many, many definitions in
> | Hoopl of this style.
> |
> | Cheers,
> | Edward
>
> _______________________________________________
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users at haskell.org
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>