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From: | szgyg |
Subject: | Re: Need help to understand a macro |
Date: | Sat, 20 Mar 2010 15:13:45 +0100 |
User-agent: | Mozilla/5.0 (Windows; U; Windows NT 5.1; hu; rv:1.9.1.8) Gecko/20100227 Lightning/1.0b1 Thunderbird/2.0 ThunderBrowse/3.2.8.1 |
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
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