patch applied (ghc): Three improvements to Template Haskell (fixes #3467)

[Duncan Coutts]

On Thu, 2009-09-10 at 06:41 -0700, Simon Peyton Jones wrote:

>   Nested top-level splices
>   ~~~~~~~~~~~~~~~~~~~~~~~~
>   Previously TH would reject this, saying that splices cannot be nested:
>   	f x = $(g $(h 'x))
>   But there is no reason for this not to work.  First $(h 'x) is run,
>   yielding code <blah> that is spliced instead of the $(h 'x). Then (g
>   <blah>) is typechecked and run, yielding code that replaces the
>   $(g ...) splice.  
>   
>   So this simply lifts the restriction.

Cool. I remember when I was working on partial evaluation / program
specialisation that this was an annoying restriction.

So now we can all write programs that generate programs that generate
programs... to our heart's content.

Duncan