Programming language design and implementation

Programming languages are typically created by designing a form of representation of a computer program, and writing an implementation for the developed concept, usually an interpreter or compiler. Interpreters are designed to read programs, usually in some variation of a text format, and perform actions based on what it reads, whereas compilers convert code to a lower level form, such as object code.

An interpreter is a program that reads another program, typically as text, as seen in languages like Python. Interpreters read code, and produce the result directly. Interpreters typically read code line by line, and parse it to convert and execute the code as operations and actions.

An interpreter is composed of two parts: a parser and an evaluator. After a program is read as input by an interpreter, it is processed by the parser. The parser breaks the program into language components to form a parse tree. The evaluator then uses the parse tree to execute the program.

• CPython, the reference implementation of Python
• IronPython, an implementation targeting the .NET Framework (written in C#)
• Jython, an implementation targeting the Java virtual machine
• PyPy, an implementation designed for speed (written in RPython)

Processes of making a programming language may differ from developer to developer; however, here is a general process of how one might create a programming language, which includes common concepts:

• Design: Design aspects are considered, such as types, syntax, semantics, and library usage to develop a language.
• Consideration: Syntax, implementation, and other factors are considered. Languages like Python interpret code at runtime, whereas languages like C++ follow an approach of basing its compiler off of C's compiler.
• Create an implementation: A first implementation is written. Compilers will convert to other formats, usually ending up as low-level as assembly, even down to binary.
• Improve your implementation: Implementations should be improved upon. Expand the programming language, aiming for it to have enough functionality to bootstrap, where a programming language is capable of writing an implementation of itself.
• Bootstrapping: If using a compiler, a developer may use the process of bootstrapping, where a compiler for a programming language is rewritten in itself. This is good for bug checking, and proving its capability. Bootstrapping also comes with the benefit of only needing to program the language in itself from there-on.