hello,
it is just a question about semantic and aside the subject of project, and
related to another subject of internal definitions that Linus is talking
about:
On Fri, Nov 18, 2022 at 5:55 PM Matt Wette<matt.wette@gmail.com> wrote:
Here is an example of an auto-coded event decoder:
(lambda (obj-id bv ix cm)
"event decoder for global"
(let*-values
(((name ix) (dec-u32 bv ix))
((interface ix) (dec-string bv ix))
((version ix) (dec-u32 bv ix)))
(values obj-id name interface version)))
i was just thinking how i would write the procedure above in Scheme+ (
https://github.com/damien-mattei/Scheme-PLUS-for-Guile ) that has feature
for multiple values.
this code could be rewritten like that:
(lambda (obj-id bv ix cm)
"event decoder for global"
{(name ix) <+ (dec-u32 bv ix)}
{(interface ix) <+ (dec-string bv ix)}
{(version ix) <+ (dec-u32 bv ix)}
(values obj-id name interface version))
note that <+ is an "operator" that allows multiple values definitions.
but it would fails to compile because of multiple redefinition of ix
variable:
scheme@(guile-user)> (use-modules (Scheme+))
scheme@(guile-user)> (lambda (obj-id bv ix cm)
"event decoder for global"
{(name ix) <+ (dec-u32 bv ix)}
{(interface ix) <+ (dec-string bv ix)}
{(version ix) <+ (dec-u32 bv ix)}
(values obj-id name interface version))
While compiling expression:
Syntax error:
unknownfile:7:0: invalid or duplicate identifier in definition in form
(lambda (obj-id bv ix cm) "event decoder for global" (<+ (name ix) (dec-u32
bv ix)) (<+ (interface ix) (dec-string bv ix)) (<+ (version ix) (dec-u32 bv
ix)) (values obj-id name interface version))
a longer and a bit unsightly solution could be:
(lambda (obj-id bv ix cm)
"event decoder for global"
(declare name interface version)
{(name ix) <v (dec-u32 bv ix)}
{(interface ix) <v (dec-string bv ix)}
{(version ix) <v (dec-u32 bv ix)}
(values obj-id name interface version))
that would be correct:
(note <v instead of <+ is a setter! for already defined values and declare
just define variables initialised by default with '() in Scheme+)
scheme@(guile-user)> (lambda (obj-id bv ix cm)
"event decoder for global"
(declare name interface version)
{(name ix) <v (dec-u32 bv ix)}
{(interface ix) <v (dec-string bv ix)}
{(version ix) <v (dec-u32 bv ix)}
(values obj-id name interface version))
;;; <stdin>:16:24: warning: possibly unbound variable `dec-u32'
;;; <stdin>:17:29: warning: possibly unbound variable `dec-string'
$3 = #<procedure 149009320 at <unknown port>:13:0 (obj-id bv ix cm)>
the first example fails not because of my Scheme+ language extension but
because in scheme redefinition is only allowed at toplevel or in the REPL.
Would it not be a good idea to allow redefinitions in Scheme and Guile not
only at toplevel or REPL but in procedure definitions and lambda, in their
bodies?
personaly i can not see any "bad" side effect or consequences... of course
it relax the possibility of code error by unchecking a redefinition of
variable but it is like in C++ where you can define private or protected
variables but even with protective language feature one can wrote bad
code...
Best regards,
Damien