Re: Q: unboxed values and polymorphism

[stt@henning.camb.inmet.com (Tucker Taft)]

Hannes Haug (Hannes.Haug@Student.Uni-Tuebingen.de) wrote:

: ...
: Sort of. Fixnums are integers in the range -2^30 ... 2^30-1. Other
: integers are interpreted as pointers to (or indices in arrays of)
: bignums or list cells. And it is not a bad idea.

:     Jon> I'm not sure what it is you are trying to do.  Make a list?
:     Jon> Make a generic list?  Make a typed polymorphic list?  Make an
:     Jon> untyped uncheckd programmer beware list?  What?

: I need it for my computer algebra nucleus. I need lisp-like dynamic
: typing. I cannot use tagged records. This would make a list cell 50%
: bigger. This would mean 33% less list cells. And this would mean 50%
: more garbage collections. I also need the type information on the stack
: for my garbage collector. I cannot use records for fixnums either. This
: would mean a "new" for every operation. My nagation takes ca. 20 nsec
: for fixnums on a 90MHz hyperSPARC. With a "new" this would be a not so
: little bit slower. Perhaps the usage of records for fixnums would even
: make some functions too big for inlining.

Rather than tagged records, which allow for "unbounded" polymorphism,
you might want to simply use a variant record.  By using an appropriate
record representation clause, you should be able to keep your list
cells down to 2 words.  You might still find a use for unbounded
polymorphism (i.e. tagged records), when you point to larger objects 
which are not simply composted of list cells.  However, if you
are essentially implementing a variant of Lisp, then I doubt if
tagged records will do much for you.  Tightly encoded variant records
seem more likely to be the answer.

:  - hannes

-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Cambridge, MA  USA