Type-checking of slot values

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

    Date: Tue, 26 Jan 88 01:28:37 PST
    From: Jon L White <edsel!jonl@labrea.Stanford.EDU>

    The two sentences you are comparing here aren't really that different:
     (1) "An implementation may or may not choose to check the type of the 
	  new value when initializing or assigning to a slot"
     (2) "An implementation is required to check the type of the value being 
	  stored in a slot only under the safest compiler safety setting and 
	  in the interpreter." 
    As I read these two, they require absolutely nothing in the way of error
    checking.  

If you read CLOS pages 1-6 and 2-23, that is clearly not the case.  The
second one requires every implementation to signal an error in certain
circumstances.

    ...nor does it 
    even imply that an implementation has to provide "compiler safety settings".

CLtL page 160.

I'd rather not get into a discussion on this mailing list of whether
Lisp should or should not be changed into a strongly-typed language.  That
belongs on some other list.