The difference between programming languages and libraries
Unless you are in it for the “fun” or the intellectual experience, building a programming language is a lot of work that might not be necessary. If your motives are strictly utilitarian, you don’t have to make a programming language when a library will do the job. Libraries are by far the most common way to extend an existing programming language to perform a new task. A library is a set of functions or classes that can be used together to write applications for some hardware or software technology. Many languages, including C and Java, are designed almost completely to revolve around a rich set of libraries. The language itself is very simple and general, while much of what a developer must learn to develop applications consists of how to use the various libraries.
The following is what libraries can do:
- Introduce new data types (classes) and provide public functions (an API) to manipulate them
- Provide a layer of abstraction on top of a set of hardware or operating system calls
The following is what libraries cannot do:
- Introduce new control structures and syntax in support of new application domains
- Embed/support new semantics within the existing language runtime system
Libraries do some things badly, so you might end up preferring to make a new language:
- Libraries often get larger and more complex than necessary.
- Libraries can have even steeper learning curves and poorer documentation than languages.
- Every so often, libraries have conflicts with other libraries.
- Applications that use libraries can become broken if the library changes incompatibly in a later version.
There is a natural evolutionary path from a library to a language. A reasonable approach to building a new language to support an application domain is to start by making or buying the best library available for that application domain. If the result does not meet your requirements in terms of supporting the domain and simplifying the task of writing programs for that domain, then you have a strong argument for a new language.
This book is about building your own language, not just building your own library. It turns out that learning about tools and techniques to implement programming languages is useful in many other contexts.
