Locating Type Errors 123 Required Types TYPE ANALYSER Inferred Types

This chapter presents a static diagnosis tool that locates type errors in untyped CLP programs without executing them. The existing prototype is specialised for the programming language CHIP [4.10], but the idea applies to any CLP language. The tool works with approximated speci cations which describe types of procedure calls and successes. The speci cations are expressed as a certain kind of term grammars. The tool automatically locates at compile time all the errors (with respect to a given speci cation) in a program. The located erroneous program fragments are (pre xes of) clauses. The tool aids the user in constructing speci cations incrementally; often a fragment of the speci cation is already suÆcient to locate an error. The presentation is informal. The focus is on the motivation of this work and on the functionality of the tool. Some related formal aspects are discussed in [4.15, 4.29]. The prototype tool is available from http://www.ida.liu.se/ ~pawpi/Diagnoser/diagnoser.html.