less worse command line editing in the perl6 repl

I’ve been doing more puttering about with perl6 lately. One of my chief complaints has been that the repl is pretty lousy, keyboard-wise. There’s no history, so I do a lot of copy and paste, and there’s no way to move left non-destructively. If you notice a typo at the beginning of your line, you’re stuffed.

This isn’t that surprising. Rakudo doesn’t ship with a readline implementation, and that’s totally reasonable. You have to install something to make it go, and the common suggestion is Linenoise. It’s easy to install with Panda, the perl6 package manager. Panda is installed with rakudobrew, if you’re using it. If not, you can just clone panda and follow the instructions.

After that: panda install Linenoise

I hit a couple problems getting it to work subsequent to that. Some of them are fixed. (Update: It looks like all of this has now been fixed if you use rakudobrew and install a fresh moar! tadzik++ FROGGS++) For one, it tried to load liblinenoise.so, even though OS X dynamic libraries are generally .dylib files. That’s fixed in the repo, and panda installs from the repo.

On the other hand, the OS X dynamic loader needs some help getting paths right. I had to fix the installed library’s identity and register a path with the MoarVM binary so that it would look for installed dynamic libraries.

For the first:

cd ~/perl6/share/perl6/site/lib
install_name_tool -id $PWD/liblinenoise.dylib liblinenoise.dylib

That sets the library file’s idea of its own identity to its installed location, rather than its build location.

For the second:

install_name_tool -add_rpath $PWD $(which moar)

…which adds the cwd to the moar binary’s library resolution path.

Now when I run perl6, I get a repl with somewhat working line editor. I can go back and forward in the line with ^B and ^F, and I back and forward in history with ^P and ^N. Unfortunately what I can’t do is use the arrow keys. I know, I know, I should probably be avoiding them, because I’m a Vim user. Too bad, I’m used to it, except when in Vim.

Strangely enough I found that the arrow keys work under tmux. It turns out that my iTerm2 profile was set to default to “application keypad mode.” Why? No idea. To turn it off, I went to Preferences → Profiles → (my default) → Keys → Load Preset… → xterm Defaults.

The simple test to see what was going on was to hit ^V then ←. If I saw \eOD, I was in keypad mode. The right thing to see was \e[D.

Now I can edit my repl entry line easily! There’s also very rudimentary tab completion, but frankly I’m not much of a tab completer. I just wanted to be able to fix my typos. (I like to pretend that my typos all come from bumpy bus rides, but sadly that’s just not true.)

Although I did a little bit of my own digging to figure the above out, almost all the real answers came from geekosaur++ and hoelzro++ and others on #perl6. Thanks, friends!

Written on May 13, 2015
🐪 perl
🏷 perl6
🧑🏽‍💻 programming