[kepler-dev] Re: zero-length arrays

[Edward A Lee]

The type of an ArrayToken is {t} where t is least upper bound
of the types of the elements.

We have talked about (and have a preliminary implementation of)
a TupleToken, which is tuple of tokens that can have heterogeneous
types.  It is exactly like a RecordToken, except that instead
of named fields, it has numbered fields.  The type inference engine
works fine with this...

Edward



At 08:11 AM 8/12/2004 -0700, Shawn Bowers wrote:
> > TF> It looks (from comments in the source) like ArrayTokens are supposed to
> > TF> have a type that is determined by the least upper bound of their
> > TF> components, but because the code generator doesn't understand 
> 'least upper
> > TF> bound', the current implementation of arrays requires that all of the
> > TF> elements have the same type exactly.  (Otherwise you could have a
> > TF> heterogeneous array, whose type would be elevated to {general}.)
> >
> > ouch... is that how Haskell and other Hindley Milner (HM) type systems
> > would do it? But then again, maybe HM is not the best for the very
> > flexible needs in a Ptolemy/Kepler like system... not sure..
>
>In the Ptolemy expression language, you can give a "heterogeneous" array
>{0, 1.0, "foo"} and the inferred type is array of string (the most general
>concrete type, right under 'general').
>
> >
> > TF> An empty array created from "{}" could have type "{general}", and 
> an empty
> > TF> array created from subarray operations, or repeat(0,"foo"), could have
> > TF> more specific types, and appending something to zero-length array could
> > TF> have the type recomputed on the resulting array (neglecting the
> > TF> non-element and its possibly 'general') type... eh?
> >
> > I think we should at least give HM a chance...
> >
> > all of these typing issues are very interesting and get even more so,
> > as we start adding "semantics"...
> >
> > another day...
> >
> > Bertram
> >
> >
> > TF>
> > TF> ...
> > TF>
> > TF> Tobin
> >
> > 
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>
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------------
Edward A. Lee, Professor
518 Cory Hall, UC Berkeley, Berkeley, CA 94720
phone: 510-642-0455, fax: 510-642-2739
eal at eecs.Berkeley.EDU, http://ptolemy.eecs.berkeley.edu/~eal