A programming language implementation is a system for executing programs written in a programming language.
There are two general approaches to programming language implementation:
- Interpretation: An interpreter takes as input a program in some language, and performs the actions written in that language on some machine.
- Compilation: A compiler takes as input a program in some language, and translates that program into some other language, which may serve as input to another interpreter or another compiler.
Notice that a compiler does not directly execute the program. Ultimately, in order to execute a program via compilation, it must be translated into a form that can serve as input to an interpreter.
When a piece of computer hardware can interpret a programming language directly, that language is called machine code. A so-called native code compiler is one that compiles a program into machine code. Actual compilation is often separated into multiple passes, like code generation (often for assembler language), assembling (generating native code), linking, loading and execution.
If a compiler of a given high level language produces another high level language it is called translator (source to source translation), which is often useful to add extensions to existing languages or to exploit good and portable implementation of other language (for example C), simplifying development.
Many combinations of interpretation and compilation are possible, and many modern programming language implementations include elements of both. For example, the Smalltalk programming language is conventionally implemented by compilation into bytecode, which is then either interpreted or compiled by a virtual machine (most popular ways is to use JIT or AOT compiler compilation). This implementation strategy has been copied by many languages since Smalltalk pioneered it in the 1970s and 1980s.
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