arrow function syntax simplified

Quildreen Motta quildreen at gmail.com
Sun Apr 1 17:09:16 PDT 2012


On 01/04/12 15:08, Allen Wirfs-Brock wrote:
>
> On Apr 1, 2012, at 8:07 AM, Quildreen Motta wrote:
>
>
> How is the above better (ignoring any controversy about line-beginning 
> separators) than:
>
> let ps = {
>    lookahead ( n) { this.current().slice(0, n || 1) },
>    current()  { this.text.slice(this.offset) },
>    move(n)  { this.clone(this.text, this.offset + 1) },
>    clone(text, offset)  {
>       let r = Object.create(this);
>       r.offset = offset || 0;
>       r.text = text || '';
>    }
> }
I forgot the object literal syntax was also getting a lightweight method 
definition syntax, my bad.

>
>>
>> You'd perhaps avoid some of the confusion on dynamic `this' by making 
>> it explicit that `this' is just an additional parameter passed over 
>> to the function — albeit implicitly.
>
>
> "this" isn't just an additional parameter and trying to turn it into 
> such just creates more confusions. this (aka self) is a characteristic 
> feature of object-oriented /methods/, not of functions. Methods only 
> have meaning in the context of an object.  It is essential to the OO 
> programming model that this/self is dynamically bounds  to the object 
> that is the target of each method invocation.  In a well designed OO 
> language the method invocation target is syntactically distinct from 
> "other parameters".  If this didn't have special OO semantics there 
> would be no reason to have special syntax and semantics for 
> defining/accessing this within a function.  However, in that case you 
> don't have a OO language, instead you have a functional language that 
> is used to provide a (low fidelity) simulation of OO constructs.
Hm, perhaps because of my mostly functional background — JS is the only 
OO language I've actually spent much time learning, — I've always seen 
methods as higher-order functions (target -> a... -> b), and the 
`object.method()' invocation pattern as just coupling single dispatching 
with a nice infix function invocation syntax.

Maybe I'm thinking more in terms of possible implementation details than 
concepts, which I'm not as familiar with.


>> It seems to work for Python, though there `self' is bound at the 
>> instantiation time.
>
> I don't believe this is correct, if you mean object instantiation 
> time.  You can view obj.meth in Python as a left-curry operation that 
> creates a new function where the first parameter of meth is pre-bound 
> to obj.  This is why Python does not have issue 3 above.
Ah, yes, you're right. The currying is done at the lookup/dispatch time.
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