What is necessary from a language implementation point of view to implement type providers like in F# 3.0?

Question

F# 3.0 adds type providers, which make it basically unnecessary to manually write or generate mappings between a DB (or another data provider) and the language/type system, because the language can query structural information from the database itself directly with type providers.

What is necessary from a language implementation point of view to add such a feature to a language?

Does it require a fully pluggable type system? Or is it more like some hidden code generator integrated into the compiler?

What's necessary to implement a new type provider for F#?