How Good Is Local Type Inference?

A partial type inference technique should come with a simple and precise specification, so that users predict its behavior and understand the error messages it produces. Local type inference techniques attain this simplicity by inferring missing type information only from the types of adjacent syntax nodes, without using global mechanisms such as unification variables. The paper reports on our experience with programming in a full-featured programming language including higher-order polymorphism, subtyping, parametric datatypes, and local type inference. On the positive side, our experiments on several nontrivial examples confirm previous hopes for the practicality of the type inference method. On the negative side, some proposed extensions mitigating known expressiveness problems turn out to be unsatisfactory on close examination. Comments University of Pennsylvania Department of Computer and Information Science Technical Report No.MSCIS-99-17. This technical report is available at ScholarlyCommons: http://repository.upenn.edu/cis_reports/180 How Good is Local Type Inference? Haruo Hosoya Benjamin C. Pierce Department of CIS Department of CIS University of Pennsylvania University of Pennsylvania [email protected] .upenn.edu [email protected] University of Pennsylvania Technical Report MS-CIS-99-17