The former.

With earlier versions, e.g. k2.8, there is a `show command to trigger a pop-up window that reminds me of Tcl/Tk, containing the values in editable fields.

The interpreter is terminal friendly and works without the GUI but it has no formatted output of tables in ASCII like in k4. x11 libraries are a dependency.

Interesting. Did anybody miss the GUI? Sounds strange that it was removed.

Yes, the "electric" GUI was incredibly fast and effective. The K2 GUI was basically the only GUI system I've ever used in which it is easier to write a GUI for a simple system than a batch command line. It looks basic and wouldn't have won any design awards, but it was crazy fast and crazy effective. See e.g. The S- spreadsheet (copied here in its entirety), see near the bottom of http://nsl.com/papers/spreadsheet.htm for screenshots and discussions

    S..t:".[`D;(;);{. y};S[]];S[.;`f]:9$D[]"
    S:D:.+(`a`b`c`d;4 6#,"")

Other examples: http://nsl.com/papers/puzzle15.htm , http://nsl.com/papers/calculator.htm

I suspect the reasons it was removed were:

(a) it was a lot to maintain compared to the rest of the k environment, as it needed to be implemented for all systems independently (X, Win, Mac at the time), and introduced dependencies that were about 10x larger than the base system.

(b) it wasn't actually a selling point - being simple and local GUI meant that while it was nice for the programmer users, it wasn't useful for end users, who usually had no K license of their own, and who expected everything to be web-able and importable to Excel.

(c) it wasn't extendable with more widgets. Needed a small HTML control or video player in your GUI? touch luck.

I believe the GUI idea is still alive, but today it can be web-based. See 1010data.com.

1010data's web UI isn't actually based on the K2-era GUI framework; it is architected as a reasonably conventional web application that happens to use K3 as a server-side language. The 1010data query language offers facilities for making data-driven UIs for interactive reports and the like, but any semantic similarity to the K2 GUI system is probably coincidental.

>any semantic similarity to the K2 GUI system is probably coincidental.

Hardly coincidental! I very much had the K gui in mind when I originally architected it (and I'm not sure I'd describe it as a "reasonably conventional web application"...)

So 1010data's purpose is to sell analytics tools to kdb+ users? Does kdb+ not come with a simple way to pipe output to a chart? For the price, I'd hope they had something more than a REPL.

1010data's analytics tools and database are entirely their own product, developed separately from kdb+. While these are implemented in K (K3, which precedes kdb+/q/K4), the end users are not K programmers any more than WordPress users are PHP programmers.