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Re: CHECK-ARG-TYPE [and CHECK-SUBSEQUENCE]
- To: David A. Moon <Moon at SCRC-TENEX at MIT-MC>
- Subject: Re: CHECK-ARG-TYPE [and CHECK-SUBSEQUENCE]
- From: JonL at PARC-MAXC
- Date: Thu, 02 Sep 1982 16:30:00 -0000
- Cc: Common-Lisp at SU-AI
- In-reply-to: Moon at SCRC-TENEX's message of Thursday, 26 August 1982, 03:04-EDT
PDP10 MacLisp and VAX/NIL have had the name CHECK-TYPE for several
years for essentially this functionality (unless someone has recently renamed
it). Since it is used to certify the type of any variable's value, it did not
include the "-ARG" part. The motivation was to have a "checker" which was
more succinct than CHECK-ARGS, but which would generally open-code the
type test (and hence introduce no delay to the non-error case).
I rather prefer the semantics you suggested, namely that the second argument
to CHECK-TYPE be a type name (given the CommonLisp treatment of type
hierarchy). At some level, I'd think a "promise" of fast type checking should
be guaranteed (in compiled code) so that persons will prefer to use this
standardized facililty; without some indication of performance, one would
be tempted to write his own in order not to slow down the common case.
If the general sequence functions continue to thrive in CommonLisp, I'd
like to suggest that the corresponding CHECK-SUBSEQUENCE macro (or
whatever renaming of it should occur) be included in CommonLisp.
CHECK-SUBSEQUENCE (<var> <start-index> <count>) &optional <typename>
provides a way to certify that <var> holds a sequence datum of the type
<typename>, or of any suitable sequence type (e.g., LIST, or STRING or
VECTOR etc) if <typename> is null; and that the indicated subsequence
in it is within the size limits.