Re: Revised straw proposal for heuristic info

["R. Kent Dybvig" <dyb@cs.indiana.edu>]

> (procedure-arity _proc_)

>   Returns information about the arity of _proc_.  If the result
>   is #F, then no information is available.  If the result
>   is an exact non-negative integer k, then _proc_ requires
>   exactly k arguments.  If the result is an inexact non-negative
>   integer n, then _proc_ requires n or more arguments.  If the
>   result is a pair, then it is a list of exact non-negative
>   integers, each of which is a number of arguments that will be
>   accepted by _proc_; the list is not necessarily exhaustive.

Why limit the list in the third case to exact non-negative integers?
By doing so, procedure-arity can't precisely describe procedures that
accept, for example, 1 or 2+ arguments.

I prefer encoding "n or more arguments" as (- -1 n), e.g., 0 or more is
-1, 1 or more is -2, etc., since this encoding does not presume support
for both exact and inexact numbers.  Also, I think that using inexact
numbers for this purpose is misleading even if it is cute.

> (procedure-source-position _proc_)

>   Returns information about the position of the source code for
>   _proc_ within the source file specified by PROCEDURE-SOURCE-FILE.
>   If the result is #F, then no information is available.  If the
>   result is an exact integer k, then k characters precede the
>   opening parenthesis of the source code for _proc_ within that
>   source file.

Procedure expression do not necessarily begin with an open parenthesis
in all implementations.  I suggest simply eliminating "the opening
parenthesis of".

> (procedure-expression _proc_)

>   Returns information about the source code for _proc_.  If the
>   result is #F, then no information is available.  If the result
>   is a pair, then it is a lambda expression in the traditional
>   representation as a list.

Source-level procedure expressions are not necessarily represented as
lists in all implementations.  (They may be after expansion.)  I
suggest replacing "as a list" with "as a datum".  Also, the text should
specify whether the expression is source-level or post-expansion, or it
should explicitly leave this unspecified.

Kent