Lua: vim.func functional utils

[justinmk]

Problem

This issue tracks some known functions that we want in vim.func.

Related: vim.iter #23233

Expected behavior

from #8677 (comment) :

• (transparent?) coroutine support https://www.lua.org/pil/9.3.html
• "once"
• memoize / LRU
• partial application (currying? but see also the caveats mentioned here counterpoint)
  • curry (this is an applied example)

[lewis6991]

nil is the very annoy params in lua because it not only none value but also absent argument. we can not tell the difference, so if we curry the method, the nil args is rejected to send or the method will return a curried function as a invalid result.

I don't think this is true. select('#', ...) should tell you the number of passed arguments, including any tailing nil's.

I would implement currying as this:

local function curry(fn, ...)
  local n, args = select('#', ...), { ... }
  return function(...)
    local fargs = {}
    for i = 1, n do
      fargs[i] = args[i]
    end
    for i = 1, select('#', ...) do
      fargs[n+i] = select(i, ...)
    end
    return fn(unpack(fargs, 1, n + n2)
  end
end

local curried = curry(f, 1, 2, 3, 4, nil, nil)

curried(5, 6, 7, nil)
-- equiv to:
-- f(1, 2, 3, 4, nil, nil, 5, 6, 7, nil)

[justinmk]

curried(5, 6, 7, nil)

Is that currying or partial application? https://stackoverflow.com/a/218055/152142

[lewis6991]

Ah yeah, it's creating a partial, which is what you usually want.

I'm sure the same concept can be used to create a currying function.