soure->source Xformer

Joe Armstrong <>
Tue Sep 23 15:04:42 CEST 2003


On Tue, 23 Sep 2003, Richard Carlsson wrote:

> 
> On Tue, 23 Sep 2003, Joe Armstrong wrote:
> 
> >   Has anybody (Luke?, Robert?) got a source->source Erlang transformer
> > that expand out
> >
> > 	- records
> > 	- funs
> > 	- list-comprehensions
> > 	- if/case/receive
> >
> > This is prettry similar to erl_lint + sys_pre_expand only brought
> > up-to-date for list-comprehensions and records.
> 
> sys_pre_expand already *does* expand away records and list
> comprehensions (do "c(foo, ['E'])." and look at the "foo.E" file).

  Sorry - I'd forgotten aabout the records - but the expansion of list
comprehensions is missing ...

> 
> Adding a pass to expand ifs to normal cases should be simple (there used
> to be a template parse transform file somewhere - under stdlib I think -
> but I can't find it in the current distribution). Or just hack
> sys_pre_expand to do it for you - it should not make any difference
> if it is done there or later (well, the debugger could be confused).

Yup - done this before :-)

> Funs should _not_ be "expanded" however, as long as you're still on this
> level - it's a *big* mistake to expose the actual implementation of
> closures until you get to the really low level code.

This where I am of two minds. One part of me says implement funs
by lambda-lifting and transforming into regular first-order code 
(and yes I know you have to "cheat" with the odd funny atom name :-)
The other part says make "proper" closures (internally) - both
approaches have advantages and disadvantages.

IMHO the difficult bit in an implementation is the layering - what goes into
which layer....




> 	/Richard
> 
> 
> Richard Carlsson ()   (This space intentionally left blank.)
> E-mail: 	WWW: http://user.it.uu.se/~richardc/
>  "Having users is like optimization: the wise course is to delay it."
>    -- Paul Graham
> 




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