Using filename in mapped command

Question

I am on Neovim, and have ToggleTerm installed. I would like to do

:nnoremap <leader><leader>r :ToggleTerm<cr>my_interpreter %<cr>

but this will just open ToggleTerm, and run my_interpreter %, which is of course wrong.

The filename isn't expanded, why is this not working?

Answer 1

I would do:

:nnoremap <expr> <leader><leader>r ':ToggleTerm<cr>my_interpreter ' . expand('%') . '<cr>'

Or in lua:

vim.keymap.set('n', '<leader><leader>r', "':ToggleTerm<cr>my_interpreter ' . expand('%')", { expr=true })

If you are using and <expr> (expression) mapping the right hand side is not sent literally but considered as an expression and it is its evaluation that is sent.

More information with: :help map-<expr>

Answer 2

Ok, after more googling, I found that the following lua command works:

vim.keymap.set(
    'n', 
    '<leader><leader>r', 
    function () 
        return ':ToggleTerm<cr>' .. 'my_interpreter ' .. vim.fn.expand("%") .. '<cr>' 
    end,
    { expr = true} 
)

Put this in your user specific init.lua, or do :lua the_command_from_above inside nvim.

See also the neovim docs on vim.keymap.set.

And as per Friedrich's request in the comments, something about how this works, or why it's equivalent to the other answer:

• the 'n' means the mapped key works in normal mode, and vim.keymap.set is automatically nore
• the anonymous function is called every time
• and expr = true tells vim that this is a map-expression

But to be fair, I'm not entirely sure why this must be a function, and not a string. If I just use a string, then I get undefined variable ":ToggleTerm" 🤷‍♂️