On Thu, 14 Jan 2010 14:42:06 +0000, you wrote:
>> All Lisps have "special forms" which are evaluated uniquely and differently
>> from function application and are therefore reserved words by another name.
>> For example, Clojure has def, if, do, let, var, quote, fn, loop, recur,
>> throw, try, monitor-enter, monitor-exit, dot, new and set!.
>
>Yes, but the special forms are not distinguishable from user defined
>macros --- and some Lisp-implemantations special forms are another
>implementations macros. E.g. you can choose to make `if' a macro that
>expands to `cond' or vice versa. I do not know whether you are
>allowed to shadow the name of special-forms.
You can in Scheme; syntactic-keyword bindings can shadow variable
bindings, and vice versa:
The following is given as an example in R5RS:
(let-syntax ((when (syntax-rules ()
((when test stmt1 stmt2 ...)
(if test
(begin stmt1
stmt2 ...))))))
(let ((if #t))
(when if (set! if 'now))
if))
Evaluating the above returns "now."
Steve Schafer
Fenestra Technologies Corp.
http://www.fenestra.com/
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