----- Original Message -----
From: "marcomaggi" <[EMAIL PROTECTED]>
To: "ikarus-users" <[email protected]>
Sent: Sunday, November 09, 2008 3:56 PM
Subject: [ikarus-users] define-macro
Help a guy out!
Both because I need it and as an exercise in learning
SYNTAX-CASE I have tried for hours to write a Common
Lisp like DEFINE-MACRO. I could not get around how to use/modify/
whatever:
(define lisp-transformer
(lambda (p)
(lambda (x)
(syntax-case x ()
((keyword . rest)
(datum->syntax (syntax keyword)
(p (syntax->datum x))))))))
nor how to change the implementation in the PLT Scheme
module "defmacro.ss".
Finally, after a lot of headbanging, I have this:
;; this-file.sls --
(import (ikarus)
(srfi lightweight-testing))
(check-set-mode! 'report-failed)
(define-syntax define-macro
(lambda (incoming)
(syntax-case incoming ()
((_ (?name ?arg ...) ?form ...)
(syntax
(define-macro ?name (lambda (?arg ...) ?form ...))))
((_ ?name ?func)
(syntax
(define-syntax ?name
(lambda (x)
(syntax-case x ()
((kwd . rest)
(datum->syntax #'kwd (apply ?func (cdr (syntax->datum
x))))))))))
)))
(check
(let ()
(define-macro (proof a b c)
`(list ,a ,b ,c))
(proof 'one 'two 'three))
=> '(one two three))
(check
(let ()
(define-macro (proof a b c)
`(,a ,(+ 1 b) ,c))
(proof list 123 'three))
=> '(124 three))
(let ()
(define-macro (false-if-exception expr)
`(guard (exc (else #f))
,expr))
(check
(false-if-exception (list 1 2 3))
=> '(1 2 3))
(check
(false-if-exception (raise 'slap))
=> #f))
(check-report)
;;; end of file
which I do not fully understand but seems to work.
Is it actually correct?
TIA
Here is one Will Clinger (I think) posted a while back on comp.lang.scheme:
(define-syntax define-macro
(lambda (x)
(syntax-case x ()
[(_ (name . params) body1 body2 ...)
#'(define-macro name (lambda params body1 body2 ...))]
[(_ name expander)
#'(define-syntax name
(lambda (y)
(syntax-case y ()
((k . args)
(let ((lst (syntax->datum #'args)))
(datum->syntax #'k (apply expander lst)))))))]
)))
Definitely easier to understand :)
Cheers
leppie
