Can we change a variable from a transformer into a procedure?
R7RS explains that (define <variable> <expression>) is the same as
(set! <variable> <expression>)
if <variable> is bound to a non-syntax value -- but if <variable>
is a syntactic keyword, then the definition would bind <variable>
to a new location.
We tested:
Some of the tested systems do not aim at R7RS compliance, but it is interesting to see the results nevertheless.
(define-syntax f
(syntax-rules ()
((_) -1)))
(define (f) -2)
(display (f))
(newline)| system | REPL | batch/compiled |
|---|---|---|
| Bigloo | -1 | |
| Chibi | -2 | -2 |
| Chicken | -1 | -2 |
| Chez | -2 | -2 |
| Cyclone | -2 | -1 |
| Gambit | -1 (error on define) |
error on define |
| Gauche | -2 | -2 |
| Guile | -2 | -2 |
| Kawa | -2 | ? |
| LIPS | -2 | |
| Loko | -2 | |
| MIT | -2 | error (Variable reference to a syntactic keyword) |
| Peroxide | -2 | |
| Racket | -2 | |
| Sagittarius | -2 | -2 |
| Scheme48 | -2 | |
| STklos (up to 1.70) | -1 | -1 |
| STklos (post v1.70) | -2 | -1 |
| scheme9 | -1 | |
| Unsyntax | -2 | duplicate definition of identifier |
| Ypsilon | -2 |
The same program was translated into Elisp, Common Lisp and Clojure:
| system | result |
|---|---|
| elisp | -2 |
| Clojure | -2 |
| Common Lisp | -2 |
(define-syntax f
(syntax-rules ()
((_) -1)))
(define (change-f)
(set! f (lambda () -2)))
(display (f))
(newline)| system | REPL | batch/compiled |
|---|---|---|
| Bigloo | Unbound variable | |
| Chez | invalid syntax | |
| Chibi | invalid use of syntax | |
| Cyclone | -2 | Error: Unbound variable |
| Chicken | -1 | -2 |
| Gambit | Macro name can't be used as a variable: f |
Macro name can't be used as a variable: f |
| Gauche | -2 | -2 |
| Guile | set! - not a transformer |
set! - not a transformer |
| Kawa | error - constant variable f is set! | unexpected exception while compiling: java.lang.NullPointerException |
| LIPS | -2 | n/a |
| Loko | invalid syntax | |
| MIT | Variable required | |
| Peroxide | cannot set non-variable f |
|
| Racket | set!: cannot mutate syntax identifier | |
| Sagittarius | syntax error | n/a |
| Scheme48 | -1 (after warning: invalid assignment) | |
| STklos 1.70 | -1 (after error: variable 'f' unbound) | error ('f' unbound) |
| Stklos post-1.70 | -2 | -1 |
| Scheme9 | -1 | n/a |
| Unsyntax | -1 (after error: not a variable transformer 'f') |
|
| Ypsilon | error in set!: misplaced syntactic keyword as variable |
The same program was translated into Elisp, Common Lisp and Clojure:
| system | result |
|---|---|
| elisp | -1 |
| Clojure | -2 |
| Common Lisp | -2 |
(In Common Lisp, the function value of f was changed with (setf (symbol-function 'f) (lambda () -2))
n/a = no compiler, or no difference between "compiled" and "running from the REPL".