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From: Thomas 'PointedEars' Lahn on 17 Jun 2010 11:05
Dmitry A. Soshnikov wrote:

> On 17.06.2010 4:53, Thomas 'PointedEars' Lahn wrote:
>> Lasse Reichstein Nielsen wrote:
>>> "Dmitry A. Soshnikov" writes:
>>>> Lasse Reichstein Nielsen wrote:
>>>>> The pattern
>>>>> [x,y] = [e1,e2];
>>>>> should be detectable at compile time, so the introduction of the
>>>>> intermediate array can be optimized away.
>>>> Moreover, it can be done syntactically without brackets, as in Python:
>> No, it can't. Check your assumptions.
>
> Did I say that I assume something?

It sure looked so: "... can be done ..., [the same] as in Python".

> I confirmed.

OK, that was easy to misunderstand.

>> the feature was designed for extracting elements from Arrays instead.
>
> Possibly, it's from what is called pattern-matching in more older
> languages (such as e.g. Erlang). There, if you want to extract elements
> from "something" where "something", one can use that pattern matching:
>
> [A, B] = [1, 2]
>
> A and B will have 1 and 2 respectively. The same:
>
> {Data, {OtherData, AndOther}} = {10, {"test", [1, 2, 3]}} to bind three
> variables.

Thanks for the example. It led me to find out that

var [data, [otherData, another]] = [10, ["test", [1, 2, 3]]];

works in JavaScript 1.8.2 (and probably all 1.7+), too (that is,

data === 10
otherData === "test"
another === [1, 2, 3]

afterwards.)


PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann
From: Dmitry A. Soshnikov on 17 Jun 2010 11:19
On 17.06.2010 19:05, Thomas 'PointedEars' Lahn wrote:

<snip>

>
> var [data, [otherData, another]] = [10, ["test", [1, 2, 3]]];
>
> works in JavaScript 1.8.2 (and probably all 1.7+), too (that is,
>
> data === 10
> otherData === "test"
> another === [1, 2, 3]
>


Yeah, moreover, pattern matching for objects also works since 1.7 as I see:

let {a: n} = {a: 10};

Thus, `n' becomes 10. It can be useful for shorthands in enumeration of
objects:

for (let {longPropertyName: name, otherProperty: other} in object) {
print(name, other);
}

Dmitry.

From: Dmitry A. Soshnikov on 17 Jun 2010 14:25
On 17.06.2010 18:16, Richard Cornford wrote:
> On Jun 17, 1:51 pm, Dmitry A. Soshnikov wrote:
>> On 17.06.2010 0:41, Lasse Reichstein Nielsen wrote:
> <snip>
>>>> Swapping without "third" can be done with simple arithmetic
>>>> operations:
>>
>>>> A = A - B
>>>> B = A + B
>>>> A = B - A
>>
>>> Try that for strings :)
>>
>> Yeah, I know sure. Just mentioned thinking about numbers at that
>> time (with numbers also can be overflow, by the way).
> <snip>
>
> With javascript's double precision floating point numbers overflows
> are possible, but loss of precision seems (much) more likely. Consider
> what will happen if A is a number at the upper range of possible
> number representations, say 1.0e308 and B is a number close to the
> smallest (positive) number, say 5.0e-324. But the numbers don't have
> to be as extreme as those:-
>
> var A = 1.0e9;
> var B = 1.0e-9;
>
> A = A - B
> B = A + B
> A = B - A
>
> // A is now zero
> // B is now 1000000000
>
> I have a vague recollection of once being shown a 'swapping' algorithm
> for signed integers (with no third variable) that used only bitwise
> operations to swap the values, avoiding any risk of overflows.
> Obviously in javascript that would only be viable for 32 bit integers,
> and adding two of those will not overflow the range of integers that
> can be represented by an IEEE double precision floating point number.

Yeah, and XOR algorithm won't help also in this case:

A ^= B;
B ^= A;
A ^= B;

// the same
// A is now zero
// B is now 1000000000

Dmitry.
From: Dmitry A. Soshnikov on 17 Jun 2010 14:30
On 17.06.2010 19:19, Dmitry A. Soshnikov wrote:

<snip>

> for (let {longPropertyName: name, otherProperty: other} in object) {
> print(name, other);
> }

Err (forgot the correct syntax). Should be "for each" and this approach
is better use to iterate an array of objects:

var array = [
{a: 10, b: 20},
{a: 30, b: 40, c: 50}
];

for each (let {a: x, b: y} in array) {
print(x, y);
}

Result:

10, 20
30, 40

Dmitry.
From: Dr J R Stockton on 18 Jun 2010 16:50
In comp.lang.javascript message <timstreater-150A94.10555217062010(a)news.
individual.net>, Thu, 17 Jun 2010 10:55:52, Tim Streater
<timstreater(a)waitrose.com> posted:

>
>Was it not "swap bytes" on an operand in the PDP-11? So you might say:
>
> swab R3 or swab (SP)
>
>for example to swap the bytes in register 3 or the top item on the stack.
>

Probably, since it is on page 10-13 of my copy of a handbook for the
LSI-11 series.

Did you ever consider 014747, which is MOV -(PC),-(PC) ?

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 IE 7.
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
Command-prompt MiniTrue is useful for viewing/searching/altering files. Free,
DOS/Win/UNIX now 2.0.6; see <URL:http://www.merlyn.demon.co.uk/pc-links.htm>.
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