CHAPTER 4 Description of ABC
CHAPTER 4 Description of ABC General Issues This chapter gives a semi-formal definition of ABC. It describes the syntax and semantics of ABC, and lists the predefined commands, functions and predicates. Values in ABC ABC has two basic types of values: numbers and texts, and three ways of making new types of values from existing ones: compounds, lists and tables. Texts, lists and tables have in common that they contain an arbitrary length progression of 'items', all of the same type. They are collectively known as trains. All values of a given type have an ordering, which means that all values of the same type can be compared with each other. This ordering is informally specified below; for a precise definition see section Order tests . Comparison of values of different types is not allowed. All values have a textual representation, and can be written and read. The built-in functions of ABC for operating on values are described in section Formulas with predefined function