Programming languages are formal systems designed to specify instructions, possessing both syntax and semantics. While they share some superficial similarities with natural languages, their purpose and scope are distinctly different. The journey of programming languages has been one of continuous evolution, moving from theoretical constructs for abstract machines to practical tools that operate on physical computers with finite resources. This evolution has shaped
how we interact with technology and the kinds of ideas we can express through computation.
Programming Languages and Natural Languages: A Complex Relationship
Programming languages bear a resemblance to natural languages in their capacity to facilitate the communication of ideas, particularly between people. Programs are generally designed to be human-readable, allowing developers to express complex concepts in a structured manner. However, a fundamental distinction lies in the types of ideas they can convey. The ideas expressible through programming languages are ultimately confined to the domain of computation, unlike the vast and nuanced range of human thought that natural languages can articulate.
The terms "computer language" and "programming language" are sometimes used interchangeably, yet some experts argue for a clear differentiation. One perspective suggests that programming languages constitute a subset of computer languages. Another view uses "computer language" to categorize languages used in computing that are not considered programming languages. Furthermore, some define a programming language as a theoretical construct for programming an abstract machine, while a computer language is the practical subset that runs on a physical computer, constrained by its hardware resources.
The Theoretical and Practical Divide
John C. Reynolds emphasized that a formal specification language is as much a programming language as any language intended for execution. He argued that even textual and graphical input formats that influence a computer's behavior should be considered programming languages, even if they are not Turing-complete. Reynolds suggested that a lack of understanding of programming language concepts is a root cause for many flaws found in input formats, highlighting the importance of formal rigor in all forms of computational instruction.
This perspective underscores the theoretical underpinnings of programming languages, viewing them as tools for defining behavior, whether for an abstract model or a concrete machine. The transition from abstract concepts to practical application on physical hardware introduces constraints and considerations that shape language design. The need to operate within finite hardware resources means that theoretical constructs must be translated into executable code, a process that involves compilers, interpreters, and other implementation details.
The Role of Implementation in Language Definition
The definition of a programming language is not solely theoretical; it is also deeply intertwined with its implementation. A reference or model implementation, which might even be written in the language it specifies, serves as a concrete manifestation of its syntax and semantics. The behavior of this implementation explicitly defines how the language operates, providing a practical guide that complements any formal specification. This interplay between theoretical definition and practical implementation is crucial for the development and understanding of programming languages, bridging the gap between abstract ideas and their execution on computing systems.
