[ANN] Proteus: local mutable variables for the masses

[Zach Tellman]

There was some discussion a few days ago about how the lack of local mutable variables were harming performance, or possibly elegance, I'm not sure.  Regardless, I fixed it: https://github.com/ztellman/proteus

Enjoy!

[Ben Wolfson]

Note:

proteus> (defmacro aif [test then else]
           (let [it (first (filter #(not (contains? &env %))
                                   (cons 'it (map #(symbol (str "it-" %)) (iterate inc 1)))))]
             `(let [~it ~test] (if ~it ~then ~else))))
#'proteus/aif
proteus> (aif (get {:x {:y 3}} :x)
              (aif (get it :y)
                   [it it-1]
                   it)
              nil)
[{:y 3} 3]
proteus> (let-mutable [x 1]
                      (aif (get {:x {:y 3}} :x)
                           (aif (get it :y)
                                (set! x [it it-1])
                                (set! x it))
                           (set! x nil))
                      x)
CompilerException java.lang.RuntimeException: Unable to resolve symbol: it-1 in this context, compiling:(NO_SOURCE_PATH:1:1)
proteus>

On Thu, Jul 11, 2013 at 6:16 PM, Zach Tellman <ztel...@gmail.com> wrote:

There was some discussion a few days ago about how the lack of local mutable variables were harming performance, or possibly elegance, I'm not sure.  Regardless, I fixed it: https://github.com/ztellman/proteus

Enjoy!

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--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which may be sweet, aromatic, fermented or spirit-based. ... Family and social life also offer numerous other occasions to consume drinks for pleasure." [Larousse, "Drink" entry]

[Zach Tellman]

Yeah, for safety's sake I need to macroexpand everything, which wipes out the &env for internal macros.  There might be a gentler way to do this, but it's not obvious to me.  If anyone has suggestions, I'd be interested in hearing them.

Zach

[Ben Wolfson]

On Thu, Jul 11, 2013 at 6:48 PM, Zach Tellman <ztel...@gmail.com> wrote:

Yeah, for safety's sake I need to macroexpand everything, which wipes out the &env for internal macros.  There might be a gentler way to do this, but it's not obvious to me.  If anyone has suggestions, I'd be interested in hearing them.

You can track the environment through expansion:

https://github.com/bwo/conditions/blob/master/test/conditions/free_test.clj#L19

The core.async internals do something similar (or did at the time of release, that code has been rewritten, apparently).

You're also missing some binding forms:

proteus> (clojure.pprint/pprint (macroexpand-1 '(let-mutable [x 1] (try (/ 1 0) (catch Exception x (set! x 2) x)))))
(clojure.core/let
 [x (new proteus.Containers$L 1)]
 (do
  (try
   (. clojure.lang.Numbers (divide 1 0))
   (catch Exception (.x x) (do (.set x 2) nil) (.x x)))))


proteus> (clojure.pprint/pprint (macroexpand-1 '(let-mutable [x 1] (letfn [(x [] 4)] (set! x 4) x))))
(clojure.core/let
 [x (new proteus.Containers$L 1)]
 (do (letfn* [x (fn* x ([] 4))] (do (.set x 4) nil) (.x x))))

[Zach Tellman]

It looks like the macroexpansion code in conditions.free is fairly generic.  What would you say to putting it into its own library?

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[Ben Wolfson]

Sure, I was considering that anyway. I'm not sure, though, whether it should be in its own library all by its lonesome or in one with at least a fairly generic name, since I've got some other macro-related utilities (specifically https://github.com/bwo/macroparser) that could all be usefully (I think) grouped together.