[Haskell-cafe] pointers for EDSL design

[oleg at okmij.org]

John Lato wrote:

> So here's a very simple expression:
>
> t1 = let v = sigGen (cnst 1) in outs v v
>
> which is what led to my question.  I'm binding the sigGen to 'v' to
> introduce sharing at the meta-level.  Would it be better to introduce
> support for this in the dsl?

Often this is not a question of preference but that of
necessity. Sharing at the meta-level may help the generator, but it
does _not_ translate into the sharing at the object level. In the
generated code, the code for 'sigGen (cnst 1)' shall be
duplicated. It could be that two csound blocks must share the same
signal source, to receive samples in parallel. Meta-level sharing
(Haskell's let) would not do. We need a construct for an object-level
let, for example

  t1 = let_ (SigGen (cnst 1)) (\v -> outs v v)

(Template Haskell can improve the syntax.)

The term `off-shoring' was coined by Walid Taha and collaborators, and
first appeared in the paper 
	Implicitly Heterogeneous Multi-Stage Programming. GPCE'05
(whose first draft was written in Feb 2004).