The School of Squiggol: A History of the Bird−Meertens Formalism

Abstract

The Bird-Meertens Formalism, colloquially known as "Squiggol", is a calculus for program transformation by equational reasoning in a function style, developed by Richard Bird and Lambert Meertens and other members of IFIP Working Group 2.1 for about two decades from the mid 1970s. One particular characteristic of the development of the Formalism is fluctuating emphasis on novel 'squiggly' notation: sometimes favouring notational exploration in the quest for conciseness and precision, and sometimes reverting to simpler and more rigid notational conventions in the interests of accessibility. This paper explores that historical ebb and flow.