Incremental addition of types and contracts

MSDN Channel9 has an excellent interview between Erik Meijer and Shriram Krishnamurthi which includes, among other things, a discussion of adding types, contracts, and verification to at least some portion of existing programs written in non-typed languages. I was especially interested by his claim that this was necessarily a problem of refactoring.

I often work in untyped languages and have learned to refactor by separating side-effects from logic, but I am curious about ways of adding contracts and type checking to portions of programs after they are written. Does anyone know of systems or papers addressing this topic?

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i haven't watched it yet, but those are some cool speakers, thanks for pointing it out. (there's a lot on c9 that sounds great, i just wish they would bloody well get some automatic speach-to-text transcripts going. i hate sitting through video/audio, i just want to read things.)

Typed Scheme

You might have a look at Typed Scheme and the related paper, The Design and Implementation of Typed Scheme, by Sam Tobin-Hochstadt and Matthias Felleisen from POPL 2008.

The idea is precisely to allow you to gracefully add (explicit) typing to a Scheme program, one module at a time.

Erlang is rich

i think Erlang is a great place to see pragmatic optional/gradual typing. i don't know of another language that comes close (but i don't know much so i might just be ignorant):



Quick Check (ok not really about types per se but still cool :-).