[PATCH] Replace define-macro with syntax-rules

[PATCH] Replace define-macro with syntax-rules

[KAction]

From: Dmitry Bogatov <KAction@gnu.org>

As I can see, definition with define-macro is hygienic and 
move to syntax-rules adds two lines of code, but define-syntax 
is considered preferable. 

WDYT?
Signed-off-by: Dmitry Bogatov <KAction@gnu.org>
---
 module/rnrs/bytevectors.scm | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/module/rnrs/bytevectors.scm b/module/rnrs/bytevectors.scm
index 9744359..856ad4a 100644
--- a/module/rnrs/bytevectors.scm
+++ b/module/rnrs/bytevectors.scm
@@ -75,9 +75,12 @@
 (load-extension (string-append "libguile-" (effective-version))
                 "scm_init_bytevectors")
 
-(define-macro (endianness sym)
-  (if (memq sym '(big little))
-      `(quote ,sym)
-      (error "unsupported endianness" sym)))
+(define-syntax endianness
+    (syntax-rules ()
+        ((_ sym)
+         (let ((qsym (quote sym)))
+             (if (memq qsym '(big little))
+                 qsym
+                 (error "unsupported endianness" qsym))))))
 
 ;;; bytevector.scm ends here
-- 
Recipients list generated via git-blame. Tell me, if you object.

Re: [PATCH] Replace define-macro with syntax-rules

[Taylan Ulrich B.]

KAction@gnu.org writes:

> From: Dmitry Bogatov <KAction@gnu.org>
>
> As I can see, definition with define-macro is hygienic and 
> move to syntax-rules adds two lines of code, but define-syntax 
> is considered preferable. 
>
> WDYT?
> Signed-off-by: Dmitry Bogatov <KAction@gnu.org>
> ---
>  module/rnrs/bytevectors.scm | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/module/rnrs/bytevectors.scm b/module/rnrs/bytevectors.scm
> index 9744359..856ad4a 100644
> --- a/module/rnrs/bytevectors.scm
> +++ b/module/rnrs/bytevectors.scm
> @@ -75,9 +75,12 @@
>  (load-extension (string-append "libguile-" (effective-version))
>                  "scm_init_bytevectors")
>  
> -(define-macro (endianness sym)
> -  (if (memq sym '(big little))
> -      `(quote ,sym)
> -      (error "unsupported endianness" sym)))
> +(define-syntax endianness
> +    (syntax-rules ()
> +        ((_ sym)
> +         (let ((qsym (quote sym)))
> +             (if (memq qsym '(big little))
> +                 qsym
> +                 (error "unsupported endianness" qsym))))))
>  
>  ;;; bytevector.scm ends here

(FYI, your mail ended up in my Gmail spam folder.  Don't know why.)

That definition is not equivalent, it moves the error to run-time.
Something like the following should be better:

(define-syntax endianness
  (syntax-rules ()
    ((_ big) 'big)
    ((_ little) 'little)))

This removes the "unsupported endianness" error and will instead raise a
generic syntax error ("source expression failed to match any pattern in
form ...").  This might just be enough, but if we want it a specific
error message could be achieved with `syntax-case', or a `syntax-error'
macro (used in an "else" clause of `syntax-rules').

Taylan

Re: [PATCH] Replace define-macro with syntax-rules

[Ian Price]

taylanbayirli@gmail.com (Taylan Ulrich B.) writes:

> (define-syntax endianness
>   (syntax-rules ()
>     ((_ big) 'big)
>     ((_ little) 'little)))
Except now whenever you use it, you only ever get big endianness. You
forgot to add big and little to the literals list.

Also, IMO, if you are using literals they should be to bound identifiers.

> This removes the "unsupported endianness" error and will instead raise a
> generic syntax error ("source expression failed to match any pattern in
> form ...").  This might just be enough, but if we want it a specific
> error message could be achieved with `syntax-case', or a `syntax-error'
> macro (used in an "else" clause of `syntax-rules').

Pattern match errors are completely useless, really.

-- 
Ian Price -- shift-reset.com

"Programming is like pinball. The reward for doing it well is
the opportunity to do it again" - from "The Wizardy Compiled"

Re: [PATCH] Replace define-macro with syntax-rules

[Taylan Ulrich B.]

Ian Price <ianprice90@googlemail.com> writes:

> taylanbayirli@gmail.com (Taylan Ulrich B.) writes:
>
>> (define-syntax endianness
>>   (syntax-rules ()
>>     ((_ big) 'big)
>>     ((_ little) 'little)))
> Except now whenever you use it, you only ever get big endianness. You
> forgot to add big and little to the literals list.

Doh!  Can't believe I made such a mistake, must write more Scheme. :)

Well, actually, it will still coincidentally work because the `big' in
`'big' (`(quote big)') will refer to the pattern variable.  (Essentially
we made an alias to `quote'.)