<html> <body> At 02:09 PM 9/9/2006, Eli Barzilay wrote: <blockquote type=cite class=cite cite="">On Sep  9, Blake McBride wrote: > > I probably mean something like procedural macros that allow you to > specify exactly what you want without trying to do it in some higher > level 4th generational descriptive pattern language.  I believe > there is an SRFI about this. Well then, `define-syntax' does just that.  When you write:   (define-syntax foo     (lambda (stx)       ...)) you bind `foo' -- as a syntax -- to a syntax->syntax transformer procedure.  How you implement the procedure is up to you -- `syntax-rules' can construct simple transformers very easily, and `syntax-case' gives you only the pattern matching part in an easy way.  But nothing prevents you to write your own body in the above definition, and you can use the basic syntax manipulation tools (syntax-e, syntax-object->datum and datum->syntax-object).</blockquote> This is very interesting to me.  If I could deal with syntax objects the way I want and go back and forth between syntax objects and scheme objects I would be able to do anything I wanted. Once I get a good understanding of all this I could better understand what the heck is going on with syntax-case. I'd like to play with this.  I did try for a few minutes and couldn't get anywhere.  For starters, on entry stx, I presume, is a syntax object representing my call.  I presume the lambda must also return a syntax object. Since stx is already a syntax object I tried: (define-syntax foo   (lambda (stx)        stx)) (foo 6) and the system hangs. If I try: (define-syntax foo   (lambda (stx)     (syntax-object->datum stx))) (foo 6) I get:  foo: return value from syntax expander was not syntax: (foo 6) If I try: (define-syntax foo   (lambda (stx)     (datum->syntax-object stx (car (syntax-object->datum stx))))) (foo 6) I get:  car: expects argument of type <pair>; given foo So if stx represents the "foo" token, how do you get to the 6? Of course if I try: (define-syntax foo   (lambda (stx)     (datum->syntax-object stx (syntax-object->datum stx)))) (foo 6) I get the system hang again (I'm now full loop). I really like your suggestion.  I just can't figure our how to get it to work at all. (I'd prefer to avoid syntax-e since it doesn't seem to be standard.) Any examples to help me grok this would be greatly appreciated. Blake McBride </body> </html>