[GHC] #11393: Ability to define INLINE pragma for all instances of a given typeclass

[GHC]

#11393: Ability to define INLINE pragma for all instances of a given typeclass
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        Reporter:  danilo2           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by danilo2:

Old description:

> Hello! I would like to request a feature that would allow me to define
> the `INLINE` pragma for all instances of a given type class. Currently
> when we are creating high-performance libraries, that strongly depend on
> type-level computations we are using a lot of typeclasses that we want to
> be cut-out during the compilation time. We can use the `INLINE` pragma to
> be sure that after type-class resolution the code will be inlined and
> hopefully strongly optimized, but we have to put the pragme in every
> single type class instance, which makes the code look ugly and is just
> impractival. So I would like to transform code like (this is just
> example, not a real-world problem solving code):
>
> {{{
>
> class Foo a b where foo :: a -> b
>
> instance Foo Int String where foo = show
>                               {-# INLINE foo #-}
> instance Foo Int Int    where foo = id
>                               {-# INLINE foo #-}
> instance Foo Int Float  where foo = fromIntegral
>                               {-# INLINE foo #-}
>
> }}}
>
> into:
>
> {{{
>
> class Foo a b where foo :: a -> b
>                     {-# INLINE foo #-}
>
> instance Foo Int String where foo = show
> instance Foo Int Int    where foo = id
> instance Foo Int Float  where foo = fromIntegral
>
> }}}
>
> I think it would be pretty easy to support such syntax and a lot of
> libraries would benefit from the design.
>
> Edit: As a small note - I've seen another way of dealing with the
> problem, namely mixing the pragmas with semicolons like that:
>
> {{{
>
> class Foo a b where foo :: a -> b
>
> instance Foo Int String where foo = show         ;{-# INLINE foo #-}
> instance Foo Int Int    where foo = id           ;{-# INLINE foo #-}
> instance Foo Int Float  where foo = fromIntegral ;{-# INLINE foo #-}
>
> }}}
>
> But this is just another ugly work-around, not a nice solution.

New description:

 Hello! I would like to request a feature that would allow me to define the
 `INLINE` pragma for all instances of a given type class. Currently when we
 are creating high-performance libraries, that strongly depend on type-
 level computations we are using a lot of typeclasses that we want to be
 cut-out during the compilation time. We can use the `INLINE` pragma to be
 sure that after type-class resolution the code will be inlined and
 hopefully strongly optimized, but we have to put the pragme in every
 single type class instance, which makes the code look ugly and is just
 impractival. So I would like to transform code like (this is just example,
 not a real-world problem solving code):

 {{{

 class Foo a b where foo :: a -> b

 instance Foo Int String where foo = show
                               {-# INLINE foo #-}
 instance Foo Int Int    where foo = id
                               {-# INLINE foo #-}
 instance Foo Int Float  where foo = fromIntegral
                               {-# INLINE foo #-}

 }}}

 into:

 {{{

 class Foo a b where foo :: a -> b
                     {-# INLINE foo #-}

 instance Foo Int String where foo = show
 instance Foo Int Int    where foo = id
 instance Foo Int Float  where foo = fromIntegral

 }}}

 I think it would be pretty easy to support such syntax and a lot of
 libraries would benefit from the design. Unfortunatelly the proposed
 design does not nicely mix with default methods in classes, where we can
 use the pragma to denote that the default implementation should be
 inlined. But if there is no default method implementation GHC rejects the
 above example, so I think we can find a nice solution for the problem.

 Edit: As a small note - I've seen another way of dealing with the problem,
 namely mixing the pragmas with semicolons like that:

 {{{

 class Foo a b where foo :: a -> b

 instance Foo Int String where foo = show         ;{-# INLINE foo #-}
 instance Foo Int Int    where foo = id           ;{-# INLINE foo #-}
 instance Foo Int Float  where foo = fromIntegral ;{-# INLINE foo #-}

 }}}

 But this is just another ugly work-around, not a nice solution.

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11393#comment:2>
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