callable objects ?

Axel Rauschmayer axel at
Tue Apr 17 15:06:18 PDT 2012

Awesome. That gives you all the building blocks for trying out object exemplars via a library.

I would add: [[HasInstance]] -> @hasInstance

On Apr 17, 2012, at 22:44 , Brendan Eich wrote:

> Brendan Eich wrote:
>> Irakli Gozalishvili wrote:
>>> It would be amazing to have clojure like protocols in JS  even without `IFn`. I think it's very good feet and very useful in JS where each library has it's own flavored API. I wrote more about it here:
>> Still hoping Mark will weigh in.
> Ok, I talked to Mark and Tom Van Cutsem, and they see no problem provided we prevent overriding built-in [[Call]] and [[Construct]] on function objects.
> Let there be private names @call and @construct (I'll spell them this way to avoid tedious imports of const bindings from "@std" or another built-in module).
> Let Clause 15.3.5 include new non-configurable, non-writable properties of function objects named by @call and @construct (built-in functions have only @call). The values are built-in and need a bit more thought than I can spare now, but see below: @call's value is close to the original value of, and @construct's value is straightforward enough I think.
> Change 11.2.2 "The new Operator" to use @construct not [[Construct]], passing the /argList// spread as actual positional parameters: (...argList).
> Change 11.2.3 "Function Calls" to use @call not [[Call]], passing the /thisValue/ and /argList/ according to the convention: (thisValue, ...argList).
> Change 11.4.3 "The typeof Operator", the table row with "Object (native or host and does implement [[Call]])" in column 1, to test not for [[Call]] and *not* for @call, rather to test [[NativeBrand]] === "Function" (see ES6 draft "Object.prototype.toString ( )").
> This last point is important: we do not want an object's typeof-type to change by giving it a @call property. But we do want to enable call and construct protocols to be built by users, by giving objects @call and @construct properties.
> This also simplifies direct proxies by allowing any proxy to have call and construct traps.
> Comments welcome.
> /be
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Dr. Axel Rauschmayer
axel at


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