Gamma and the chemical reaction model: fifteen years after

Gamma was originally proposed in 1986 as a formalism for the definition of programs without artificial sequentiality. The basic idea underlying the formalism is to describe computation as a form of chemical reaction on a collection of individual pieces of data. Due to the very minimal nature of the language, and its absence of sequential bias, it has been possible to exploit this initial paradigm in various directions. This paper reviews most of the work around Gamma considered as a programming or as a specification language. A special emphasis is placed on unexpected applications of the chemical reaction model, showing that this paradigm has been a source of inspiration in various research areas