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Can programming be liberated from the von Neumann style?

1978/08/01 by John Backus · 2,595 citations
Computer Science · Mathematics · #Algebra over a field #Algebraic expression #Algebraic number #Computability, Logic, AI Algorithms #Computer science #Formal Methods in Verification #Functional programming #Logic, programming, and type systems #Mathematics #Programming language #Programming paradigm #Programming style #Pure mathematics #Semantics (computer science) #Style (visual arts) #Theoretical computer science #Von Neumann architecture

paper · pdf · doi:10.1145/359576.359579

published in Communications of the ACM 21(8), 613-641 (Association for Computing Machinery)

openalex publication_date 1978/08/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

Conventional programming languages are growing ever more enormous, but not stronger. Inherent defects at the most basic level cause them to be both fat and weak: their primitive word-at-a-time style of programming inherited from their common ancestor—the von Neumann computer, their close coupling of semantics to state transitions, their division of programming into a world of expressions and a world of statements, their inability to effectively use powerful combining forms for building new programs from existing ones, and their lack of useful mathematical properties for reasoning about programs. An alternative functional style of programming is founded on the use of combining forms for creating programs. Functional programs deal with structured data, are often nonrepetitive and nonrecursive, are hierarchically constructed, do not name their arguments, and do not require the complex machinery of procedure declarations to become generally applicable. Combining forms can use high level programs to build still higher level ones in a style not possible in conventional languages. Associated with the functional style of programming is an algebra of programs whose variables range over programs and whose operations are combining forms. This algebra can be used to transform programs and to solve equations whose “unknowns” are programs in much the same way one transforms equations in high school algebra. These transformations are given by algebraic laws and are carried out in the same language in which programs are written. Combining forms are chosen not only for their programming power but also for the power of their associated algebraic laws. General theorems of the algebra give the detailed behavior and termination conditions for large classes of programs. A new class of computing systems uses the functional programming style both in its programming language and in its state transition rules. Unlike von Neumann languages, these systems have semantics loosely coupled to states—only one state transition occurs per major computation.

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