The name compiler has been given to a computer program which will accept as data a program in a problem-oriented language, such as Algol or Fortran, and produce as output a computer-oriented code which, after possibly some further processing by an assembler or loader, will be capable of being obeyed by a computer and produce results equivalent to those defined by the program in the problem-oriented language. This definition is rather vague and has to be as the word compiler is used for rather a wide range of computer programs with very different characteristics.

In this book, the problem-oriented language to be compiled will be assumed to be as machine independent and as complex as a language like Fortran or Algol. Most examples will be drawn from one or other of these languages. There is a bias towards scientific languages of this type in the techniques to be described although, of course, many of the techniques will be applicable in general The output from the compiler will be defined in machine orders for a hypothetical computer which will be similar to most of the single accumulator computers in use today.