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    <p>It is very possible to do exactly that in Racket, and in a much shorter way than done above. There are two (not-really) tricks involved:</p> <ol> <li><p>Using Racket's <a href="http://docs.racket-lang.org/reference/__top.html#%28form._%28%28quote._~23~25kernel%29._~23~25top%29%29"><code>#%top</code></a> macro makes it possible to create such bindings-out-of-thin-air. This macro is getting used implicitly around any variable reference that is unbound ("top" because these things are references to toplevel variables).</p></li> <li><p>Macros become much simpler if you make them do the necessary minimum, and leave the rest to a function.</p></li> </ol> <p>Here's the complete code with comments and tests (the actual code is tiny, ~10 lines).</p> <pre><code>#lang racket ;; we're going to define our own #%top, so make the real one available (require (only-in racket [#%top real-top])) ;; in case you want to use this thing as a library for other code (provide #%top) ;; non-trick#1: doing the real work in a function is almost trivial (define (c...r path) (apply compose (map (λ(x) (case x [(#\a) car] [(#\d) cdr])) path))) ;; non-trick#2: define our own #%top, which expands to the above in ;; case of a `c[ad]*r', or to the real `#%top' otherwise. (define-syntax (#%top stx) (syntax-case stx () [(_ . id) (let ([m (regexp-match #rx"^c([ad]*)r$" (symbol-&gt;string (syntax-e #'id)))]) (if m #`(c...r '#,(string-&gt;list (cadr m))) #'(real-top . id)))])) ;; Tests, to see that it works: (caadadr '(1 (2 (3 4)) 5 6)) (let ([f caadadr]) (f '(1 (2 (3 4)) 5 6))) ; works even as a value (cr 'bleh) (cadr '(1 2 3)) ; uses the actual `cadr' since it's bound, ;; (cadr '(1)) ; to see this, note this error message ;; (caddddr '(1)) ; versus the error in this case (let ([cr list]) (cr 'bleh)) ; lexical scope is still respected </code></pre>
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    1. COI would +1 this many times if I were able to. Very nice!
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      1. USChris Jester-Young
    2. COExcellent! This solution is what I wanted, thanks! Racket is a truly beautiful and powerful language.
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      1. USRacket Noob
    3. CO@RacketNoob Most of the Racket devs recommend How to Design Programs. It's not a Racket manual, and it probably doesn't cover `#%top`, but it's still a useful book to read.
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