"Generalized Algebraic Data Structures" have become a a hot new topic. They have recently been added to the GHC compiler. They support the construction, maintenance, and propagation of semantic properties of programs using powerful old ideas about types (the Curry-Howard Isomorphism) in surprisingly easy to understand new ways. The language Omega was designed and implemented to demonstrate their utility. Here a a few talks I gave that explains how they work. Also class lectures
for 6.10 We show how to build a quasiquoter for a simple mathematical expression language. Although the example is small, it demonstrates all aspects of building a quasiquoter. We do not mean to suggest that one gains much from a quasiquoter for such a small language relative to using abstract syntax directly except from a pedagogical point of view---this is just a tutorial!
An ingenious set of combinators for expressing pattern matching in a type-safe way. No ADTs required. Opens up the possibility of programming languages where we can declare new binding forms just as we declare new functions. abstract: Macros still have not made their way into typed higher-order programming languages such as Haskell and Standard ML. Therefore, to extend the expressiveness of Haskell or Standard ML gradually, one must express new linguistic features in terms of functions that fit within the static type systems of these languages. This is particularly challenging when introducing features that span across multiple types and that bind variables. We address this challenge by developing, in a step-by-step manner, mechanisms for encoding patterns and pattern matching in Haskell in a type-safe way.
au:chlipala Ur introduces richer type system features into FP. Ur is functional, pure, statically-typed, and strict. Ur supports metaprogramming based on row types. Ur/Web is standard library and associated rules for parsing and optimization. Ur/Web supports construction of dynamic web applications backed by SQL databases. The signature of the standard library is such that well-typed Ur/Web programs "don't go wrong" in a very broad sense. They also may not: * Suffer from any kinds of code-injection attacks * Return invalid HTML * Contain dead intra-application links * Have mismatches between HTML forms and the fields expected by their handlers It is also possible to use metaprogramming to build significant application pieces by analysis of type structure - demo includes an ML-style functor for building an admin interface for an arbitrary SQL table. The Ur/Web compiler also produces very efficient object code that does not use gc