Some dynamically typed languages use hybrid approaches - e.g. Ruby has Fixnum and Bignum for integers - but you're correct that additional precision isn't free.

Some dynamically typed languages use hybrid approaches - e.g. Ruby has Fixnum and Bignum for integers - but you're correct that additional precision isn't free. I don't know how much slower, but in theory such hybrid approaches can allow the common case to be just as fast or fast enough (tm) while still returning the correct results for the uncommon case (depending on how much the runtime or compiler can prove about the range of your numbers to enable the fast path.) EDIT: Poor phrasing...