According to Q documentation, Q supports only 3 implicit parameters x, y, z: https://web.archive.org/web/20190213035913/http://code.kx.co...

They're just variables like any other; {[x;y;z] x+yz} is almost exactly the same as {x+yz}

I tested and seems, that x is the first implicit parameter, y - second, z - third. It is as stated in their online documentation. When you try following example:

  {y+x*z}[1;2;3]

It gives result:

5

And in Q you cannot define implicit parameters with names, for example,: a, b, c. But You can define parameters explicitly:

  {[a;b;c]a+b*c}[1;2;3]

I still think that their implicit parameters are keywords. Similarly as keyword 'it' in Kotlin programming language is used to refer to the single parameter of the lambda expression.

In KatLang there are no predefined implicit parameter names. The user is the one who defines implicit parameters by declaring the implicit parameter names.

No. They are not keywords. The program:

    x:42;
    f:{[a]x+a}

is the same as:

    x=42;
    f=function(a){return x+a}

Thanks for explaining! But how about this example:

  x:42
  {x+1}[5]

It results in

  6

It seems like you can define variables with the name 'x', but when you do not have explicit parameters, then the identifier 'x' is used to refer to the first implicit parameter, y - for second and z - for the third parameter. In context of implicit parameters x, y and z acts like predefined keywords.

q's functions don't capture the environment, so that's the same as:

    a:42
    {[a]a+1}[5]

and as in javascript:

    a=42;
    f=function(a){return a+1}

and when i say they don't capture the environment, i mean this:

    f:{[g] {g+x}}

doesn't do anything except generate errors (° there are benefits to this approach!) because the inner function (that we are returning) sees the "global" g and not the one lexically scoped in the function (a better way to say it: no closures).

Can you explain the difference little bit more, Maybe using Javascript pseudocode as comparable example? I want to understand how Q is different from KatLang. The problem with me is that I do not know where I can try Q code, therefore I rely only on the documentation fragments I can find.

Last I checked there was a free download with an email on kx.com

Yes, the first unknown identifier becomes the first parameter, next unknown identifier becomes next parameter and so on...

More specifically: the first unknown identifier becomes the first parameter for the closest algorithm defined with {} brackets. Properties (also called named algorithms) are defined as {} context. And KatLang program also is defined as {} context. I call it Second order algorithm - algorithms can contain another algorithms. First order algorithm is something defined between commas or semicolons. But inside brackets () or {} you can define second order algorithm.

You might like looking at how Dyalog handles higher-order functions; John Scholes really put this beautiful presentation together about using them as a depth-first search reusable function https://www.youtube.com/watch?v=DsZdfnlh_d0 and if you haven't seen it, you should!