1.2.3 Semantic entities

Data types are specified in the semantic entity module. The syntax is quite like type definition in ordinary programming languages. Examples are ``value = number $\vert$ truth-value'' and ``number =$<$ integer''. Here, truth-value is a primitive data type. =$<$ denotes a sort inclusion, which means sort number is included in sort integer with open bound.

Only data types are defined in this module, without any notation about how to evaluate or manipulate them. Actions and yielders on data are defined as semantic functions.