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Advanced type systems often need some form of type inference to reduce the burden of explicit typing, but type inference often leads to poor error messages for ill-typed programs. This work pursues a new approach to constructing compilers and presenting typeerror messages in which the type-checker itself does not produce the messages. Instead, it is an oracle for a search procedure that finds similar programs that do type-check. Our two-fold goal is to improve error messages while simplifying compiler construction.Our primary implementation and evaluation is for Caml, a language with full type inference. We also present a prototype for C++ template functions, where type instantiation is implicit. A key extension is making our approach robust even when the program has multiple independent type errors.

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