Re: Need help to understand a macro

[szgyg]

Josef Wolf wrote:
> I am trying to understand the defstruct macro from the "teach yourself
> scheme in fixnum days" tutorial, which can be found in chapter 9 at
> http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-11.html#node_chap_9
>
> My first question is of a more generic type. For a better understanding
> how macros work, I'd like to have a way to show what expansion a macro
> would generate when it would be used. E.g., I'd like to do something
> like
>
>   (show-expansion (defstruct tree height girth age leaf-shape leaf-color))
>
> and get what the expansion of this macro would produce:
>
>   (begin
>     (define make-tree
>       (lambda fvfv
>         [ ... and so on ... ]

Use the trick from the inexplicable JRM's Syntax-rules Primer for the 
Merely Eccentric[1], wrap the output with quote:

...
(let ((ff (map (lambda (f) (if (pair? f) (car f) f))
               ff)))
  `'(begin
;  ^
      (define ,(string->symbol
                (string-append "make-" s-s))
...


[1]
http://www.xs4all.nl/~hipster/lib/scheme/gauche/define-syntax-primer.txt