Monday, March 9, 2015

Riddle 2 Answer

This is somewhat esoteric, and I wouldn’t be surprised if very few people had any idea what I was even asking. I discovered this largely by chance, while fiddling around with function bytecode, though I think it could be deduced from observation without that.

So, the answer:

:: is usually taught as a sui generis operator, called “global amend”, which has the specific behavior (when used as a verb inside a function) of setting a global variable (instead of the local one that : would set in the same place). No connection is typically drawn between it and any other operator (other than :).

However, I’m pretty sure this is inaccurate. While obviously I don’t know for certain, I strongly suspect that there is no code anywhere in the q binary saying that :: is defined as “global amend”. Rather, it is a specific case of the dyadic “f:” pattern, where f is some dyadic function—e.g. dyadic +:, -:, *:, etc.

These all have the same behavior—x f:y is defined as x:x f y.

Additionally, when used inside functions on variables that have not been identified by the compiler as locals, they modify (and if necessary, create), global variables.

q){a:1;a+:1;a}[]
2
q)a
'a
q){a+:1}[]
q)a
1
q)

It follows that if f is :, then the operation involved is assignment, and so x gets y assigned to it, as a global variable if not identified as a local variable.

In fact, this can be seen in the same way:

q){a:1;a::2;a}[]
2
q)a
'a
q){a::2}[]
q)a
2
q)

Thus arises “global amend”.

If anything, the “create view” sense of :: must be the special case, as ordinarily, dyadic f: verbs behave identically inside and outside functions.

Labels: , ,

1 Comments:

At April 17, 2019 at 7:20 PM , Blogger madin said...

I really like these replica Gucci bags!!!replica luxury gucci handbags uk It is definitely recommended to buy here, the quality is perfect,replica gucci mens messenger bags the color is the same as the real Gucci, can't wait to put them on!

 

Post a Comment

Subscribe to Post Comments [Atom]

<< Home