[Haskell-cafe] jhc speed

[John Meacham]

On Sun, Feb 22, 2009 at 07:25:26AM -0700, John A. De Goes wrote:
>
> Is there any conceivable factoring of GHC that would allow you to  
> sandwich the core of jhc in between the front and back ends of GHC? Or  
> are the architectures so fundamentally incompatible as to make this  
> impossible?

Well, it wouldn't really be useful sandwiched between the front and back
end of ghc, the main advantages jhc has over ghc's model are in its
lower level optimizations closer to the back end. Feeding ghc core into
jhc shouldn't be impossible. Oddly enough, I have written a ghc back end
for jhc, mainly for testing purposes rather than a serious back end.

The tricky part isn't so much the translation of ghc to jhc core, the
type system and representation are quite similar, but the difference in
the primitives that the two systems expect to exist. for instance, ghc
has high level primitives, such as operations on Integers and primitive
types that high signedness. While jhcs primitives are much lower level,
it has no special concept of Integer for instance, you implement Integer
either in pure haskell code or FFI bindings to GMP or some other way,
and jhc's primitive numerical types are simply bit patterns with no
interpretation, for instance

data Int = I Bits32_
data Word = W Bits32_

and the only thing that makes Int signed and Word not is in the 'Num'
instances for those types.

That said, i don't see any reason a ghc-core front end for jhc wouldn't
be possible, an adapter library could be written to provide ghc style
primitives on top of the jhc ones. It would certainly be an interesting
project.


        John


-- 
John Meacham - ⑆repetae.net⑆john⑈