Interactive programming environment for language offer many advantages over traditional batch-oriented ones, such as immediate static analysis. One form of analysis is type checking, yet type checking in this setting for languages with common features like overloading has received little attention. We implement an interactive type checker for the polymorphic type system of ML with overloading. The implementation was produced automatically from an attribute grammar using the Synthesizer Generator, an attribute evaluator generator. Type inference then is accomplished via attribute evaluation so that if the evaluation is done incrementally, then type inference becomes incremental as well.