[rntz]

It has nothing to do with compilation. It has to do with static typing -- that, before ever evaluating something, you typecheck it. It is perfectly feasible to interpret a statically typed language -- SML/NJ for example, includes an interpreter for SML. However, statically typed languages are generally easier to fully compile than dynamic languages; SML/NJ also includes a compiler for SML.

[jvoorhis]

Exactly. You can pass Maybe objects in Ruby as a convention, but the extra layers of indirection probably aren't buying you much. There is no way to enforce the contract.