Re: Type-checking of slot values

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: Tue, 26 Jan 88 13:30:23 PST
    From: kempf%hplabsz@hplabs.HP.COM

    >      
    >      If CLOS is defined is such a way that acceptable performance is only
    >      achievable on "special purpose" hardware [e.g., a defclass is far too
    >      slow to be a substitute for defstruct], then I suspect it will be subject
    >      to Deutsch's Dictum:

    > I don't think that the type checking has anything to do with good
    > performance. The important thing for good performance is that  an
    > implementation an optimize slot access based on :type information. I
    > don't want to take that away from CLOS, or CLtL.

    Sorry, but I think you're wrong. On stock hardware, FIXNUM + is one
    instruction, and a compiler which can deduce when to use it will always
    win over one that can't.

What does this have to do with a requirement that a particular construct
shall signal an error in a particular circumstance?

I think you two are using the phrase "type checking" to mean two different
things.

Note how I resist the urge to point out that a certain vendor's
processor, which said vendor claims is the only stock hardware anyone
would ever want to use, and has in fact succeeded in convincing several
other corporations of the merits of that idea, has a Common Lisp +
instruction.