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Re: specification by implications and example

This page is part of the web mail archives of SRFI 17 from before July 7th, 2015. The new archives for SRFI 17 contain all messages, not just those from before July 7th, 2015.

Shriram Krishnamurthi <shriram@xxxxxxxxxxx> writes:

> You should also edit the
> "Standard setters" section to be of the form
>   (setter car-proc) --> set-car!
> where car-proc is eq? to the built-in primitive car, and so forth,
> rather than the current format.

I agree, though I don't see the point of using `car-proc'
rather than `car'.  It seems unnecessary to me.

--- srfi-17.html	Sun Jan 16 17:46:20 2000
+++ srfi-17.html.new	Mon Jan 17 00:16:58 2000
@@ -155,21 +155,40 @@
 is more intuitive, and has the big advantage that many
 existing functions already have proper setters.
 My tentative recommendation is alternative 1.
+The formal definition is thus:
+(define-syntax set!
+  (syntax-rules ()
+    ((set! (proc arg ...) value)  ;; Assuming Alternative 1
+     ((setter proc) arg ... value))
+    ;; ((set! (proc arg ...) value) ;; Assuming Alternative 2
+    ;;  ((setter proc) value arg ...))
+    ((set! var value)
+     (%%builtin-set! var value))))
+- where <code>%%builtin-set!</code> is the R5RS version of <code>set!</code>,
+and <code>setter</code> is a new standard procedure that maps procedures
+to their setters.  If the procedure has no setter, then <code>setter</code>
+signals an error.
 <h2>Standard setters</h2>
 The following standard procedures have pre-defined setters:
-(set! (car x) v) == (set-car! x v)
-(set! (cdr x) v) == (set-cdr! x v)
-(set! (caar x) v) == (set-car! (car x) v)
-(set! (cadr x) v) == (set-car! (cdr x) v)
+(setter car) --> set-car!
+(setter cdr) --> set-cdr!
+(setter caar) --> (lambda (x v) (set-car! (car x) v))
+;; Hence: (set! (caar x) v) == (set-car! (car x) v)
+(setter cadr) --> (lambda (x v) (set-car! (cdr x) v))
-(set! (caXXr x) v) == (set-car! (cXXr x) v)
-(set! (cdXXr x) v) == (set-cdr! (cXXr x) v)
-(set! (string-ref x i) v) == (string-set! x i v)
-(set! (vector-ref x i) v) == (vector-set! x i v)
+(setter caXXr) --> (lambda (x v) (set-car! (cXXr x) v))
+(setter cdXXr) --> (lambda (x v) (set-cdr! (cXXr x) v))
+(setter string-ref) -> string-set!
+(setter vector-ref) -> vector-set!
+(Here <code>car</code>, <code>set-car!</code>, and so on refer
+to their initial values in <code>(scheme-report-environment 5)</code>.)
@@ -301,7 +320,7 @@
     <address>Editor: <a href="mailto:srfi-editors@xxxxxxxxxxxx";>Mike Sperber</a></address>
 <!-- Created: Wed Nov 10 03:14:43 PST 1999 -->
 <!-- hhmts start -->
-Last modified: Sun Jan 16 10:45:36 MET 2000
+Last modified: Sun Jan 16 17:45:11 PST 2000
 <!-- hhmts end -->

	--Per Bothner
per@xxxxxxxxxxx   http://www.bothner.com/~per/