Question About the Variable Allocator

[Noah Lavine]

Hello,

I've always been puzzled about part of the variable allocator. In
module/language/tree-il/analyze.scm, we deal with allocations, which
are hash tables that say where in the stack each local variable goes.
The maps are two level, symbol - {lambda - location}. The reason
given is that different lambdas could have different variables with
the same symbol.

But if I understand correctly, each variable also gets a gensym, and
the gensyms are globally unique. So wouldn't it be possible to use the
gensyms as keys instead, and only have a single level map? If so, why
don't we do it?

Thanks,
Noah

Re: Question About the Variable Allocator

[Andy Wingo]

Hi Noah,

On Sun 03 Jun 2012 16:20, Noah Lavine noah.b.lav...@gmail.com writes:

 I've always been puzzled about part of the variable allocator. In
 module/language/tree-il/analyze.scm, we deal with allocations, which
 are hash tables that say where in the stack each local variable goes.
 The maps are two level, symbol - {lambda - location}. The reason
 given is that different lambdas could have different variables with
 the same symbol.

 But if I understand correctly, each variable also gets a gensym, and
 the gensyms are globally unique. So wouldn't it be possible to use the
 gensyms as keys instead, and only have a single level map? If so, why
 don't we do it?

AFAIR the reason is not to permit multiple lexically bound variables
with the same gensym, but to provide for different allocations of the
same variable in different closures.

Thus a variable might be at local 5 in one closure, free variable 3 in
another, free variable 6 in another, etc.

Cheers,

Andy
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