Mill Computing, Inc. Forums The Mill Architecture Why not encode data types in metadata? Reply To: Why not encode data types in metadata?

Ivan Godard
Post count: 689

No idea what happened to the original post; it doesn’t show on the Forum logs. However, I can address the question implied by the title: types in metadata.

A dynamic language like SmallTalk must keep a runtime representation of type in order to resolve the meaning of the executable. This gives second-order power and flexibility: with cleverness and SmallTalk you can brush your teeth. But type resolution is not fast.

Most programs, even those in second-order languages, are in fact first-order and bindings can be fully resolved at compile time. The rare cases where you really need second-order you can kludge around by having (first-order) programs write (first-order) programs which are then compiled. Our software is full of such generators – it’s how we can retarget for different family members based on a specification. But all steps are compiled, and everything that can be done at compile time is done then, which includes all static typing. So there’s no reason to carry type in the metadata at runtime.

The compile step also elides type transformations that are no-ops in the execution. With meta-typng every transform of an operand from int to unsigned would have to be an explicit runtime op to change the metadata even though it did nothing to change the operand value. Think how many place Foo is changed to const Foo. Ouch.