On Jul 12, 2014, at 6:43 PM, Brian Adkins <racketus...@lojic.com> wrote:
> On Jul 12, 2014, at 6:19 PM, Daniel Prager wrote:
>
>> Hi Brian
>>
>> r >= 0 && r <= 4 && c >= 0 && c <= r
>>
>>
>> implies
>>
>> 0 <= c <= r <= 4
>>
>>
>> Or using prefix and the variable-arity of <=:
>>
>> (define (is-pos r c)
>> (<= 0 c r 4))
>>
>>
>> which I think works well for clarity, concision, and efficiency.
>>
>> Dan
>
> Very nice observation; I like it. I've always felt the variable-arity of lisp
> was a cool feature. I switched to a struct for the arg, but the following
> works:
>
> (defpat (is-pos? (pos r c))
> (<= 0 c r 4))
>
> I probably won't keep my defpat macro, at least not in its present form (for
> one, it only handles a single arg); there's probably a balance between being
> concise and being general/flexible.
Although define/match is definitely more powerful, if you want it, this would
probably be a good version of what you want that would handle multiple
arguments: (I’ll reply again if I get one to work with optional and/or
keyword-arguments)
(define-syntax defpat
(syntax-rules ()
[(defpat (f arg-pat ...) body ...)
(defpat f (match-lambda** [(arg-pat ...) body ...]))]
[(defpat id expr)
(define id expr)]))
>
> I finished the program, but it's very raw - I haven't tried to match the
> Racket style, be idiomatic, etc., just rushed through it to get a rough idea
> of how it compares:
>
> https://gist.github.com/lojic/14aefacc29ab5a88fa98
>
> I'll come back to it after I get some more experience and improve it. Despite
> the questionable utility of these exercises, I always run into something that
> causes me to learn something valuable about Racket.
>
>
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