Dylan's type system

[Glenn S. Burke <gsb>]

   Date: Wed, 30 Sep 1992 18:46:49 +0100
   From: Jonathan Bachrach <Jonathan.Bachrach@ircam.fr>
   . . .
   2. non-specialized parameters

   It would be nice to be able to specify the type of a parameter without
   incurring the dispatch penalty.  Let's say that a parameter has the
   same type in all the methods for a particular generic-function.  The
   programmer really doesn't want to incur the overhead of specialization
   for this parameter, because the specialization is really only
   performing a kind of type-checking.  Perhaps there could be a flag (or
   maybe sealing a class does this now) for turning off dispatching when
   a parameter has only one specializer (where dispatching is really just
   doing a kind of type-checking anyways).

The issue of whether to do type checking vs. doing "dispatching"
should be relegated to the implementation and perhaps more general
optimization suggestions, and need not be specified in the language.
I can imagine an implementation where this sort of optimization is
performed dynamically and automatically, and furthermore it doesn't
necessarily require that the parameter have the same type in all
methods of the generic function, only in the subset being selected
from.

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