[Haskell-cafe] jhc speed

Luke Palmer lrpalmer at gmail.com
Sun Feb 22 10:22:36 EST 2009

On Sun, Feb 22, 2009 at 8:15 AM, John Meacham <john at repetae.net> wrote:

> On Sun, Feb 22, 2009 at 03:36:34PM +0100, Peter Verswyvelen wrote:
> > Would it be possible to separate the frontend (Haskell to Core) and
> backend
> > (Core to machine code) from the Haskell compilers (requiring a standard
> Core
> > language?)
> > I'm not sure how many extensions required a change to the Core language.
> Well, it depends on what you mean by 'core'. If you mean a desugared
> version of haskell, I think such a front end could be quite useful.

By the way, coming up pretty soon, I will need a desugared
*annotated*Haskell for Dana.  If anybody has something like this in
the works, I'd love
to help with it.  If it does not exist by the time I need it, I will make
it, so if anyone is interested in working on it with me, let me know :-)


> in
> particular, I'd like to see a standalone implementation of template
> haskell. If you mean something lower level, as in the ghc core
> intermediate language the compiler uses internally, or jhc's core or
> grin representation, things get a bit more tricky.
> Although many core languages are somewhat similar, based on a typed
> lambda calculus of some sort, the details will differ, and translating
> between them can be lossy.
> For instance, looking at jhc core:
> http://repetae.net/computer/jhc/manual.html#jhc-core-type-system
> you can see it has a very rich language for dealing with strictness and
> boxedness. For instances, a boxed value known to be in WHNF actually has a
> different _type_ than one that is possibly unevaluated. Such
> distinctions are quite useful for jhc's back end but not so much for
> ghc's, hence ghc core doesn't make that distinction and any translation
> between the two would 'lose' that useful information.
> In other cases things are even worse, for instance ghc has a powerful
> type equality concept in its core language which jhc has no counterpart
> for, so that information will be lost on translation. But losing that
> information will actually cause the core to not type check, since ghc
> core can type some things jhc core cannot (and vice versa) so coercions
> or other mechanisms to bypass the type system will have to be
> introduced.
> So, it is certainly possible to translate between the two, in fact, I
> made a jhc core -> ghc core translator, but the code it produced was
> necessarily riddled with unsafeCoerce#'s for everywhere the type systems
> didn't quite match up.
>        John
> --
> John Meacham - ⑆repetae.net⑆john⑈
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