Jacob Matthews came to town this past weekend for several events, and on Monday gave a fabulous talk at Northeastern on multi-language systems. The experience made me proud to be a member of both the Northeastern PRL and the PLT research family. Jacob's work looks like it could be very useful, and I hope to apply it to several of my research projects. And the presentation was fantastic: he was entertaining and charismatic, and our group was a lively and interactive audience.
He's been talking for some time about how when programs interact between typed and untyped languages, "contracts fall right out." I was looking forward to finding out how, and he kept telling me that once I saw it it would be obvious. It had sounded rather magical to me, but sure enough, about halfway through his talk it became totally obvious! If a typed language is to use an expression from an untyped language in any useful way, it'll have to have a dynamic check to make sure the expression really was of the right type. But of course, you can't in general dynamically check the type of a procedure, so contracts are a natural solution!