We propose a type system ML F that generalizes ML with first-class polymorphism as in System F. We perform partial type reconstruction. As in ML and in opposition to System F, each typable expression admits a principal type, which can be inferred. Furthermore, all expressions of ML are well-typed, with a possibly more general type than in ML, without any need for type annotation. Only arguments of functions that are used polymorphically must be annotated, which allows to type all expressions of System F as well.

We propose a type system MLF that generalizes ML with first-class polymorphism as in System F. We perform partial type reconstruction. As in ML and in opposition to System F, each typable expression admits a principal type, which can be inferred. Furthermore, all expressions of ML are well-typed, with a possibly more general type than in ML, without any need for type annotation. Only arguments of functions that are used polymorphically must be annotated, which allows to type all expressions of System F as well.

The quest for type inference with first-classpolymorphic types Programming languages considerably benefit from static type-checking. In practice however, types may sometimes trammel programmers, for two opposite reasons. On the one hand, type anno-tations may quickly become a burden to write; while they usefully serve as documentation for toplevel functions, they also obfuscatethe code when every local function must be decorated. On the other hand, since types are only approximations, any type system willreject programs that are perfectly well-behaved and that could be accepted by another more expressive one; hence, sharp program-mers may be irritated in such situations.