Using Funcrefs/lambdas with wiki_map_link_create

[savq]

Description:

Currently wiki.vim doesn't support passing funcrefs/lambdas to the wiki_map_link_create option (because of strange VimL behavior).

Minimal working example

If we create a lambda: let CreateLoudLinks = {x -> toupper(x) . '!'}, then:

This works

echo exists('*CreateLoudLinks')             " string
" = 1

echo call(CreateLoudLinks, ['hello world']) " symbol
" = HELLO WORLD!

But this doesn't work

echo exists(CreateLoudLinks)                   " symbol
" = E729: using Funcref as a String

echo call('*CreateLoudLinks', ['hello world']) " string
" = E117: Unknown function: CreateLinkLinks

The problem

The exists function always expects a string, however, the call function will fail if it receives a funcref as a string (but not as a symbol).

Suggested solution

In the source code the relevant bit seems to be:

" wiki.vim/autoload/wiki/link/word.vim

if !empty(g:wiki_map_link_create) && exists('*' . g:wiki_map_link_create)
  let l:url = call(g:wiki_map_link_create, [a:url])
endif

Allowing the user to pass a funcref, and typecheck wiki_map_link_create here, before calling exists and call seems to me like a reasonable workaround for the inconsistency between the two functions.

[lervag]

I agree this would be nice, but unfortunately, it is not possible. The reason is that the option names are all lowercase. Function names must start with a capital letter, see :help E704.

Note, this should really be just a minor inconvenience, i.e. that you need two lines instead of one, e.g.:

" We can't do this:
let g:wiki_map_link_create = {x -> toupper(x) . '!'}

" But this works
let CreateLoudLinks = {x -> toupper(x) . '!'}
let g:wiki_map_link_create = 'CreateLoudLinks'

[savq]

Yes, you're right. I made sure to name the lambda in the example because passing it directly wouldn't work.

On the other hand, the example you gave won't work either. If I understand correctly, when creating the lambda, it'll be stored in Vim's symbol table (:let), not in it's function table (:function); and because of this, passing the name of the lamda to call as a string will fail, you'd have to pass it as a symbol (and it needs to start with a capital letter for that to work so we're back where we started).

Anyways, there seems to be a lot of arbitrary restrictions from vimL's part to solve this. I'm closing the issue for now, since this was more of an inquiry than a bug.

Thanks for working on wiki.vim!

[lervag]

Yes, you're right. ...

And you're right. My example does not work, and, of course, I should have tested it before posting! I think your understanding is correct.

There are some idiosyncrasies in vimL, but with time I have found it quite nice to work with. Still, I agree this capital letter thing is a silly and unnecessary restriction. I don't know why it is there. Perhaps there is a good reason.

Thanks for working on wiki.vim!

My pleasure! Thanks for the interest and for using it :)

[savq]

Hey @lervag,

I decided to revisit this issue recently because it seems that since I first posted it, Neovim added a mechanism to convert Lua functions to Vim funcrefs. In practice this means that in a Lua config file one could write:

vim.g.wiki_map_link_create = function(txt) return txt:lower():gsub("%s+", "-") end

Lua won't complain about the capitalization of the variable, which is pretty much what I wanted in the first place.

Allowing this from wiki.vim only requires one to check if the variable is a funcref before calling exists.