Hello all,<div> </div><div>I am reading through the PLT Scheme Guide section on Generating Macros (<a href="http://docs.plt-scheme.org/guide/pattern-macros.html#(part._.Macro-.Generating_.Macros)">http://docs.plt-scheme.org/guide/pattern-macros.html#(part._.Macro-.Generating_.Macros)</a> A number of the examples in this section depend on the macro define-get/put-id, which is defined (seemingly just as the appropriate macroexpansion for one case rather than for the general case) as :<div> <table cellspacing="0" class="schemeblock"><tbody><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> (<a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/misc..ss)._define-syntax-rule))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">define-syntax-rule</a> (define-get/put-id id get put!)</td> </tr><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> (<a href="http://docs.plt-scheme.org/reference/define.html#(form._((lib._scheme/private/define..ss)._define-syntax))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">define-syntax</a> clock</td> </tr><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> (<a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._syntax-id-rules))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">syntax-id-rules</a> (<a href="http://docs.plt-scheme.org/reference/set_.html#(form._((quote._~23~25kernel)._set!))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">set!</a>)</td> </tr><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> [(<a href="http://docs.plt-scheme.org/reference/set_.html#(form._((quote._~23~25kernel)._set!))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">set!</a> clock e) (put-clock! e)]</td> </tr><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> [(clock a (<a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">...</a> <a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">...</a>)) ((get-clock) a (<a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">...</a> <a href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))" class="schemesyntaxlink" style="text-decoration: none; color: black; font-weight: bold; ">...</a>))]</td> </tr><tr><td style="padding-left: 0px; padding-right: 0px; vertical-align: baseline; "> [clock (get-clock)]))) </td></tr></tbody></table></div><div>I simply adapted it to the general case and got:</div><div> </div><blockquote class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: 0px;"> (define-syntax-rule (define-get/put-id id get put!) (define-syntax id (syntax-id-rules (set!) [(set! id e) (put! e)] [(id a (... ...)) ((get) a (... ...))] [id (get)])))</blockquote> <div><div> </div><div>Which works, surprisingly, and confuses me. Generally define-syntax does not evaluate the first argument but uses it as a symbol naming the item in the syntax, but in this case, id is a identifier which gets evaluated so that the passed value of id is used as the actual syntax. Does define-syntax check in the environment and use the literal symbol as its name unless it has a defined value as an identifier? I tried to look this up in the documentation for define-syntax but quickly got confused.</div> <div> </div><div>Thanks,</div><div> </div><div>Adam</div></div></div>