Using a multiline closure to execute commands in vimscript

Question

I'm writing a script in which I am in need of closure functionalities. Take this function, for instance:

func! SetOpNorm(norm_comm, motion_key = 'y')
    let l:norm_comm = a:norm_comm
    let l:motion_key = a:motion_key
    let s:OpFun = { type, ... ->
        \ let l:NormFun = { sel ->
            \ sil exe 'normal!' l:norm_comm
            \ sil exe "normal! \<del>"
        \ }
        \ call function('s:MapOverOp', [l:NormFun, l:motion_key, a:type] + a:000)() }
    set opfunc=s:OpFun
endfunc

The script would work except for the fact that vimscript closures accept an expr1 as their bodies and not a list of commands. Is there a way to work around this limitation?

I also tried using local functions to achieve the same result:

func! SetOpNorm(norm_comm, motion_key = 'y')
    let l:norm_comm = a:norm_comm
    let l:motion_key = a:motion_key
    func! OpFun(type, ...)
        func! NormFun(sel)
            sil exe 'normal!' l:norm_comm
            sil exe "normal! \<del>"
        endfunc
        call function('s:MapOverOp', [function('NormFun'), l:motion_key, a:type] + a:000)()
    endfunc
    set opfunc=OpFun
endfunc

But after some testing I think that this doesn't work as the inner local functions do not capture their sorrounding context.

Answer 1

See :h func-closure to declare inner function as closure.

For an example of g@ implementation using closures you can look into my plugin source code: vim-opera.