local function eval (prog)
    local env = {}
    for _, fn in ipairs (prog) do
        fn (env)
    end
end

local function keywords_for (apply)
    return function (word_list)
        local keywords = {}
        for _, word in ipairs (word_list) do
            keywords[word] = apply
        end
        return setmetatable (keywords, {__call = function (t, ...) return apply(...) end})
    end
end

local function let (var)
    local _let = function (val)
        return function (env)
            if type (val) == "function" then
                val = val (env)
            end
            env[var] = val
        end
    end
    return keywords_for (_let) { "equal", "be" }
end

local function get (var)
    return function (env)
        return env[var]
    end
end

local function add (x)
    local _add = function (y)
        return function (env)
            if type (x) == "function" then
                x = x (env)
            end

            if type (y) == "function" then
                y = y (env)
            end
            if type (y) == "table" then
                print (next(y))
            end
            return x + y
        end
    end
    return keywords_for (_add) { "to", "with" }
end

local function show (val)
    local _show = function (env)
        if type (val) == "function" then
            val = val (env)
        end

        print (val)
    end

    return _show
end

eval {
    let "x" .equal (1) ;
    let "y" .be (2) ;
    let "z" (3) ;
    show (add (get "x") .to (get "y")) ;
    show (add (get "y") .with (get "z")) ;
}