Ponies!

Fluttershy.lua

function Fluttershy(f, ...)
    local decl = {...}
    return function(...)
        local arg = {...}
        for arg_i = 1, math.ceil(#decl/2) do
            if type(arg[arg_i]) ~= decl[arg_i*2-1] then
                arg[arg_i] = decl[arg_i*2]
            end
        end
        return f(unpack(arg))
    end
end

x = Fluttershy(print,
    "string", "not provided!",
    "number", -9999,
    "table", {}
)
print(x(1, 333))

function Assertershy(f, ...)
    local decl = {...}
    return function(...)
        local arg = {...}
        for arg_i = 1, #arg do
            assert(type(arg[arg_i]) == decl[arg_i], "no")
        end
        return f(unpack(arg))
    end
end

x = Assertershy(print,
    "string",
    "number",
    "table"
)
print(x(1, 333, {}))