Utility module to simplify initializing locals from tables or modules.

from.lua

local debug = require 'debug'
-- from.lua
-- supports some useful shortcuts when creating locals from tables or modules
--   require 'from'
--   local sin,cos,tan = slots(3) from(math)
--   local import,printf = slots(2) from 'pl.utils'
--   local pretty,utils,xml = slots(3) from 'pl.*'
--
-- Uses the debug library, so it's not very fast - only use for top-level initialization!

local finfo = {}
local unpack = table.unpack or unpack

function slots (n)
    local f = debug.getinfo(2,'f').func
    if not finfo[f] then
        finfo[f] = {first = 1}
    end
    finfo[f].nslots = n
    local res = {}
    for i = 1,n do res[i] = true end
    return unpack(res)
end

local function requirex (mod,level)
    local ok, res = pcall(require,mod)
    if not ok then
        error(res,level)
    else
        return res
    end
end

function from (T)    
    local f = debug.getinfo(2).func
    local fi = finfo[f]
    local nslots,first = fi.nslots,fi.first
    if type(T) == 'string' then -- we are given a module
        local wild = T:match '(.+%.)%*$'
        if not wild then
            T = requirex (T,3)
        else -- proxy table where indexing requires the submodule
            T = setmetatable({},{ __index = function(t,mod)
                return requirex(wild..mod,4)
            end})
        end
    end
    local slot = first
    -- collect all the active locals
    local locals, append = {}, table.insert
    while true do
        local loc,v = debug.getlocal(2,slot)
        if not loc then break end
        append(locals,loc)
        slot = slot + 1
    end
    for i = #locals-nslots+1,#locals do
        local idx = i+first-1
        debug.setlocal(2,idx,T[locals[i]])
    end
    fi.first = #locals
end