Type Inference for Objects with Base Types

We present a type inference algorithm for the underlying lan guage and type system of a logic (AL [2]) of Abadi and Leino. We approach the problem by follow ing the techniques used by Palsberg and his coauthors [7, 9] whereby, using a language-based repres ntation of types, we construct an automaton to recognise a least-shape type derivation. To overcome technical problems caused in part by the weaker s ubtype relation and base types, we introduce a generalisation of types which we term pretypes. A a pleasant consequence, pretypes give rise to a natural notion of presolution which allow us to give a cleaner characterisation of least-shape type derivation.