Arbitrary-precision integers are not that slow if they're implemented the way most Lisp implementations do it. For a strongly-typed language, you would need on

Arbitrary-precision integers are not that slow if they're implemented the way most Lisp implementations do it. For a strongly-typed language, you would need only one tag bit: if the low-order bit is 0, then the remaining bits of a pointer-sized word, shifted right 1 bit, are the value; no heap storage or indirection is required, and addition and subtraction require no fixup afterwards as long as there was no overflow. Only if the low-order bit of an operand is 1, or if there's overflow, do you have to trap out to the general case which handles heap allocation. Yes, this is slower than ordinary fixed-width integer arithmetic, as a couple of conditional branches are required, but it's nowhere near the price of heap-allocating every integer.