[gazarsgo]

Not in the compiler, but enjoy a Microsoft Research paper about Steno, a C# library that claims to be superior to stream fusion (section 8.2): http://research.microsoft.com/pubs/173946/paper-pldi.pdf

In case anyone is unaware, LINQ lets you represent queries as a series of function calls which it represents as a series of Expression objects and an in-memory AST.

[seanmcdirmid]

There is also the dynamic language run-time (DLR), which as a generalization of LINQ (to support statements) is pretty powerful when writing up these tools on .NET. I use it often in my work.