This text promotes the disciplined construction of procedural programs from formal specifications. As such it can be used in conjunction with any of the more conventional programming texts which teach a mixture of ‘coding’ in a specific language and ad hoc algorithm design.

The awareness of the need for a more methodical approach to program construction is epitomised by the use of phrases such as ‘software engineering’, ‘mathematical theory of programming’, and ‘science of programming’. The hitherto all-too-familiar practices of ‘designing’ a program ‘as you write it’ and ‘patching’ wrong programs being more appropriate to a cottage industry rather than a key activity in the current technological revolution.

The cost of producing hardware is decreasing while the production of software (programs) is becoming more expensive by the day. The complexity and importance of programs is also growing phenomenally, so much so that the high cost of producing them can only be justified when they are reliable and do what they are supposed to do – when they are correct.

No methodology can exist by which we can produce a program to perform an arbitrary task. Consequently that is not the aim of the book. What we shall do is to show how, by using a Program Design Language and templates for your chosen target language, you can develop programs from certain forms of specification.

Although programming is essentially a practical activity, the degree of formality adopted throughout the development process means that sufficient information is available to enable correctness proofs to be investigated if and when required.