A Practical Approach to Type Inference for EuLisp

Lisp applications need to show a reasonable cost-beneet relationship between the ooered expressiveness and their demand for storage and run-time. Drawbacks in eeciency, apparent in Lisp as a dynamically typed programming language, can be avoided by optimizations. Statically inferred type information can be decisive for the success of these optimizations. This paper describes a practical approach to type inference realized in a module and application compiler for EuLisp. The approach is partly related to Milner-style poly-morphic type inference, but diiers by describing functions with generic type schemes. Dependencies between argument and result types can be expressed more precisely by using generic type schemes of several lines than by using the common one-line type schemes. Generic type schemes contain types of a reened complementary lattice and bounded type variables. Besides standard and deened types so-called strategic types (e.g. singleton, zero, number-list) are combined into the type lattice. Local, global and control ow inference using generic type schemes with reened types generate precise typings of deened functions. Due to module compilation, inferred type schemes of exported functions can be stored in export interfaces, so they may be reused when imported elsewhere.