Simon Peyton Jones FRS (born 18 January 1958) is a British computer scientist who researches the implementation and applications of functional programming languages, particularly lazy functional programming. He is an honorary Professor of Computer Science at the University of Glasgow and co-supervises PhD students at the University of Cambridge.

This book is about implementations, not languages, it will make no attempt to extol the virtues of functional languages or the functional programming style. Instead this book will assume that the reader is familiar with functional programming; those without this familiarity may find it heavy going.

The first part describes how to translate a high-level functional language into an intermediate language, called the lambda calculus, including detailed coverage of pattern-matching and type-checking.

The second part begins with a simple implementation of the lambda calculus, based on graph reduction, and then develops a number of refinements and alternatives, such as supercombinators, full laziness and SK combinators.

Finally, the third part describes the G-machine, a sophisticated implementation of graph reduction, which provides a dramatic increase in performance over the implementations described earlier.