Type System in Programming Languages

Type system provides a precise descriptionof a programming language. This is a prerequisite for theimplementation and use of language. It also conducts mechanical andtransparent type-checking on programs to prevent the occurrence ofexecution error during the running of programs. So, it can be said that,on the one hand, type system works as a formal tool to do mathematicalanalysis of language; on the other hand, it is a formal method forrigorously and precisely designing and implementing language. In thispaper, some basic concepts of type system are discussed first. And then, theimplementation of a graph-rewriting-based functional language ---Sclean's type system is given in details. It is hoped that the proposedmethod of using and implementing type system is of practical usefulness.