Type error feedback via analytic program repair.

We introduce Analytic Program Repair, a data-driven strategy for providing feedback for type-errors via repairs for the erroneous program. Our strategy is based on insight that similar errors have similar repairs. Thus, we show how to use a training dataset of pairs of ill-typed programs and their fixed versions to: (1) learn a collection of candidate repair templates by abstracting and partitioning the edits made in the training set into a representative set of templates; (2) predict the appropriate template from a given error, by training multi-class classifiers on the repair templates used in the training set; (3) synthesize a concrete repair from the template by enumerating and ranking correct (e.g. well-typed) terms matching the predicted template. We have implemented our approach in Rite: a type error reporting tool for OCaml programs. We present an evaluation of the accuracy and efficiency of Rite on a corpus of 4,500 ill-typed Ocaml programs drawn from two instances of an introductory programming course, and a user-study of the quality of the generated error messages that shows the locations and final repair quality to be better than the state-of-the-art tool in a statistically-significant manner.