[ASYNC-91] (CLJS) 'and' does not short circuit within go block in clojurescript Created: 14/Sep/14  Updated: 14/Sep/18

Status: Open
Project: core.async
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Defect Priority: Minor
Reporter: Jan Krueger Assignee: Unassigned
Resolution: Unresolved Votes: 3
Labels: None

core.async 0.1.338.0-5c5012-alpha


I have the following piece of ClojureScript code within a go block:

(and (vector? x) (= (first x) :some-key)) ...)

This generates the following piece of JavaScript code for the cond case:

if (40 === f) { return d = b[9], f = cljs.core.vector_QMARK_.call(null, d), d = cljs.core.first.call(null, d), d = cljs.core._EQ_.call(null, d, new cljs.core.Keyword(null, "some-key", "some-key", -978969032)), cljs.core.truth_(f && d) ? b[1] = 42 : b[1] = 43, new cljs.core.Keyword(null, "recur", "recur", -437573268); }

This looks to me like both and arguments would actually get evaluated. As a result my code crashes whenever it hits this cond case and 'x' is not seqable.

Comment by Francis Avila [ 25/Sep/14 2:52 AM ]

CLJS-864 is likely the same issue. (It also has a small test project to reproduce.)

Comment by Rangel Spasov [ 07/Nov/16 4:29 AM ]

This happened to me as well with the latest version of core.async on ClojureScript 0.2.395.

I would bump this to not minor since it severely breaks the promise that (and ...) makes.

(def cards :loading)
(go (and (vector? cards) (< 0 (count cards))))

This throws an exception like this:

No protocol method ICounted.-count defined for type cljs.core/Keyword: :loading

I was able to go around this by nesting the checks like this:
(go (if (vector? cards)
(if (< 0 (count cards))
(println "counting cards..."))))

Comment by Mike Fikes [ 14/Sep/18 10:15 AM ]

If you

(macroexpand '(go (and (vector? cards) (< 0 (count cards)))))

you will see that arguments to the js* special form are lifted out and let-bound, causing evaluation of code that the special form would never evaluate.

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