Function composition operator in Lua using __concat, which might not be the best operator to use.

composition.lua

debug.setmetatable(function() end, {
	__concat = function(self, with)
		return function(...)
			return self(with(...))
		end
	end
})

local sin = math.sin
print((sin .. sin)(5)) --sin(sin(5))
(print .. string.reverse)("Hello, world!") --print(string.reverse("Hello, world!"))