Octave-backend improvements

I’m having a bit of a pause between the exams, so I’m doing some hacking on the new Octave backend for Cantor. Thing are going very well, probably better (especially faster) that I expected.

The basic input-output sending between Cantor and the command-line process was working some time ago, and I recently added support for embedding graphics into the worksheet.

This week I was working on cosmetics: Autocompletion, syntax highlighting and pop-up help.

Completion for functions and variables

Completion was easy, octave provides a completion_matches() function which takes a string argument and return all functions and variables starting with that string.

Highlighter - there can be only one.

Syntax help was also quite straightforward, through the use of Octave’s built-in help() command. Highlighting was where I spent most of the time, because as a command-line program Octave has no native support for it.

There’s a handy command called ‘who’ that lists all currently visible variables, so I retrieved the variable name list with it and used it in the highlighter. I then hardcoded a list of all recognised operators and keywords.

The toughest nut was getting a list of all functions from Octave. There’s no (at least known to me) equivalent to ‘who’ for functions, so I had to improvise. I didn’t want to hardcode all the functions, as is done for the Maxima backend, because, as we all know, hardcoding is bad, and there’s always the possibility of future changes to Octave language. The closest I could get is using completion_matches() with an empty string, but that returns all the internal constants, environment variables, and files in the current directory. I filtered them out the best I could, and the end result work well, despite there being more that 1600 functions.

Embedded plots in Cantor

Another think I worked on this week is getting as much plotting code as possible from C++ to an octave script. This not only unclutters the worksheet (there used to be a long line of commands instead of cantor_plot#d()), but makes simple changes to plotting faster by not requiring a recompile. Tweaking the size of the plot to prevent it from filling the whole page didn’t even need a new session, just an update to the script.