Reader handling of the @ character

Reader handling of the @ character

[Duncan Mak]

Hello all,

I'm playing with the Alex Shinn match.scm macro again and I noticed that it
doesn't load in Kawa,

I think it's failing because of the handling of the @ character, probably
due to how the splice operator was implemented.

I tried the following in Chez, this is what I see with this test
syntax-rules macro:

$ chez
Chez Scheme Version 9.5.2
Copyright 1984-2019 Cisco Systems, Inc.
> (define-syntax test
    (syntax-rules (@)
      ((test @ x y z) (list x y z))))
> (test @ 1 2 3)
(1 2 3)
> (test 1 2 3)
Exception: invalid syntax (test 1 2 3)
Type (debug) to enter the debugger.
>


The same macro doesn't work in Kawa 3.1.1:

$ kawa
#|kawa:1|# (define-syntax test
#|.....2|#   (syntax-rules (@)
#|.....3|#     ((test @ x y z) (list x y z))))
#|.....4|#
/dev/tty:2:20: invalid character #\)
#|kawa:5|# (test @ 1 2 3)
/dev/tty:5:2: warning - no declaration seen for test
/dev/tty:5:2: unbound location: test
at gnu.mapping.DynamicLocation.get(DynamicLocation.java:36)
at atInteractiveLevel-2.run(tty:5)
at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:290)
at gnu.expr.ModuleExp.evalModule(ModuleExp.java:211)
at kawa.Shell.run(Shell.java:289)
at kawa.Shell.run(Shell.java:196)
at kawa.Shell.run(Shell.java:183)
at kawa.repl.processArgs(repl.java:724)
at kawa.repl.main(repl.java:830)

-- 
Duncan.

Re: Reader handling of the @ character

[Per Bothner]

On 6/28/20 6:44 PM, Duncan Mak via Kawa wrote:
> Hello all,
> 
> I'm playing with the Alex Shinn match.scm macro again and I noticed that it
> doesn't load in Kawa,
> 
> I think it's failing because of the handling of the @ character  probably
> due to how the splice operator was implemented.

This seems to work:

(define-syntax test
   (syntax-rules (|@|)
     ((test @ x y z) (list x y z))))

The --r7rs flag also works.

-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/

Re: Reader handling of the @ character

[Per Bothner]

On 6/28/20 8:04 PM, Per Bothner wrote:
> This seems to work:
> 
> (define-syntax test
>    (syntax-rules (|@|)
>      ((test @ x y z) (list x y z))))
> 
> The --r7rs flag also works.
> 

In private email I was asked about |@| and --r7rs.

The slice operator
    @expression
is converted by the Kawa reader into:
   ($splice$ expression)

The vertical bars in |@| makes @ into a regular
symbol and disables the special treatment of the @ character.

The --r7rs command-line flag disables Kawa extensions that
conflict with strict R7RS compatibility:

https://www.gnu.org/software/kawa/Options.html#Options-for-language-selection
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/

Re: Reader handling of the @ character

[Damien MATTEI]

thanks,

my mail was intend to be in the mailing list.

Le 29/06/2020 à 16:05, Per Bothner a écrit :
> On 6/28/20 8:04 PM, Per Bothner wrote:
>> This seems to work:
>>
>> (define-syntax test
>>    (syntax-rules (|@|)
>>      ((test @ x y z) (list x y z))))
>>
>> The --r7rs flag also works.
>>
>
> In private email I was asked about |@| and --r7rs.
>
> The slice operator
>    @expression
> is converted by the Kawa reader into:
>   ($splice$ expression)
>
> The vertical bars in |@| makes @ into a regular
> symbol and disables the special treatment of the @ character.
>
> The --r7rs command-line flag disables Kawa extensions that
> conflict with strict R7RS compatibility:
>
> https://www.gnu.org/software/kawa/Options.html#Options-for-language-selection 
>

Re: Reader handling of the @ character

[Per Bothner]

On 6/29/20 3:52 PM, Damien MATTEI wrote:
> thanks,
> 
> my mail was intend to be in the mailing list.

I guessed that, which is why I replied publicly,
but without identification ...


-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/