Type Checking

The role of type checking is to verify that every expression and subexpression is used in a consistent way within the program. In SMALL, compound expressions are built up from subexpressions in the way explained in Chapters 8 and 9, using the operators M _RES , M _CONT ,M _SEL , M _DEUNION and M _CONSTR . The subexpressions which are the arguments of such an operator cannot have arbitrary types, but have to obey a number of laws. These type laws are verified by the type checker. Furthermore, the type checker derives the type of the compound expression from the types of its subexpressions.