WIP: Run hook functions before & after line execution

[x4lldux]

Runs *pre-exec-hook* & *post-exec-hook* functions before/after execution of a line. Can be used to time how long a command took:

(var *last-command-duration* 0)
(var last-command-start 0)

(var *pre-exec-hook* (fn [&] (set last-command-start (os/clock))))
(var *post-exec-hook* (fn [&]
                        (set *last-command-duration*
                             (- (os/clock) last-command-start))))

[andrewchambers]

I don't fully understand the use for this feature, if I want to time something usually I would just write a time function.

[x4lldux]

Borrowed the idea from ZSH. It's usually used to enhance prompt and timing is just an example (though I'm often wandering how long does something takes only after starting it ;) ). This is needed for another PR which allows cd - go to previous directory.

[andrewchambers]

I understand - I am still unsure, I will need to think about it and read the zsh documentation.

[andrewchambers]

It seems to me this patch breaks multi line input.

[x4lldux]

Should be easy to fix. Basically need to do the same thing you do in want-implicit-parens and detect that. I'll test it in few days.

[andrewchambers]

Right, I am leaning towards allowing the repl changes to hide the exit codes, in which case that fix may be able to go there.

[pauldub]

There is a kind of hook commonly found in shells which is executed right before showing the prompt (and sometimes also after showing it).

This is used by direnv integrations, which I must currently call in my prompt function.

For reference:

• ZSH has precmd_functions http://zsh.sourceforge.net/Doc/Release/Functions.html#index-functions_002c-hook
• bash has $PROMPT_COMMAND https://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/x264.html
• fish has --on-event fish_prompt https://fishshell.com/docs/current/commands.html#fish_prompt
• elvish has @edit:before-readline` https://manpages.debian.org/testing/elvish/elvish-edit.7.en.html#Hooks

[x4lldux]

@pauldub You're right, equivalent of $PROMPT_COMMAND/precmd_function should be added. Calling direnv in *prompt* is kind a hackish and entangles concerns.

[andrewchambers]

I like direnv, so that is a good argument for me.

[x4lldux]

Once changes to repl in #161 are done, I will update this & add precmd hook also.

[andrewchambers]

I would prefer on-crash be renamed to on-error or something else, it isn't necessarily a 'crash'. I know one use for this hook is what nixos does, which is to offer a list of packages for a user to install if a binary is missing.

[x4lldux]

Sure, so *post-crash-hook* -> *post-error-hook*?
Fefora has something similar. Use cases for those hooks are many! I saw a precmd hook function that changes terminal's profile so the background is red when you ssh to a remote server just to be extra alert.