pure

function pure(body,env)
    return assert(load("return function(_ENV) return "..body.." end"))
    ()(env or {})
end
--
-- x=1
-- local y=2
-- fn=pure[[function(print)
--   x=10
--   y=20
--   print(x,y)
-- end]]
-- fn(print)
-- print(x,y)

function isolated(s)
    if type(s)=="string" then return pure(s) end
    return function(body) return pure(body,s) end
end
--
-- x=1 fn=isolated{x=10,print=print}[[ function() print(x) end ]] fn(print) print(x)

function pure_check()
    local i,r,n,v,f
    i=0 r={} f=debug.getinfo(2,"f").func
    while true do
        i=i+1 n,v=debug.getupvalue(f,i)
        if n==nil then break end
        if n~="_ENV" then table.insert(r,n) end
    end
    if #r>0 then
        error("pure_check fail: you must define\n\tlocal "..table.concat(r,","),2)
    end
end
--[[
global_a="global_a"
local upvalue_a="upvalue_a"
function test(v1) pure_check() local _ENV={G=_G}
    -- local upvalue_a
    upvalue_a="local_a"
    local z=upvalue_a..v1
    G.print(z,G.global_a)
end
test "error"
]]