CHAPTER 2: Lexical and Textual Structure

Programs are written by human programmers, and read by their authors or by other programmers for checking and maintenance purposes; they are also processed by compilers and other automatic tools. The need to accommodate these various forms of communication permeates every level of consideration of a programming language, including the most immediate levels where we are only concerned with the physical appearance of a program text.

The lexical and textual structures of a programming language are of course important for ease of program compilation, and for compilation- time detection of errors. The importance of lexical and textual structures is even greater for ease of reading and understanding programs - in particular, for detection of logical errors - and for ease of teaching the language. We believe that our understanding of programs can be greatly simplified if our intuition is able to rely on textual forms that convey the logical structure of the program. This is the justification for giving major consideration to readability and teachability in the design of lexical and textual structures in Ada; moreover, special attention has been devoted to structural analogies.