As mentioned in Section 1.2, the behaviour of a module may be described in programming language form. This chapter describes the facilities in VHDL which are drawn from the familiar programming language repertoire. If you are familiar with the Ada programming language, you will notice the similarity with that language. This is both a convenience and a nuisance. The convenience is that you don't have much to learn to use these VHDL facilities. The problem is that the facilities are not as comprehensive as those of Ada, though they are certainly adequate for most modeling purposes.