Editing Interpreter (computing) (section)

{{Short description|Program that executes source code without a separate compilation step}}

[[File:W3sDesign Interpreter Design Pattern UML.jpg|thumb|300px|W3sDesign Interpreter Design Pattern [[Unified Modeling Language|UML]]]]
{{Program execution}}

In [[computer science]], an '''interpreter''' is a [[computer program]] that directly [[execution (computers)|executes]] instructions written in a [[Programming language|programming]] or [[scripting language]], without requiring them previously to have been [[Compiler|compiled]] into a [[machine language]] program. An interpreter generally uses one of the following strategies for program execution:

# [[Parse]] the [[source code]] and perform its behavior directly;
# [[Translator (computing)|Translate]] source code into some efficient [[intermediate representation]] or [[object code]] and immediately execute that;
# Explicitly execute stored precompiled [[bytecode]]<ref>''In this sense, the [[Central processing unit|CPU]] is also an interpreter, of machine instructions.''</ref> made by a [[compiler]] and matched with the interpreter's [[virtual machine]].

Early versions of [[Lisp programming language]] and [[BASIC interpreter|minicomputer and microcomputer BASIC dialects]] would be examples of the first type. [[Perl]], [[Raku (programming language)|Raku]], [[Python (programming language)|Python]], [[MATLAB]], and [[Ruby (programming language)|Ruby]] are examples of the second, while [[UCSD Pascal]] is an example of the third type. Source programs are compiled ahead of time and stored as machine independent code, which is then [[Linker (computing)|linked]] at run-time and executed by an interpreter and/or compiler (for [[Just-in-time compilation|JIT]] systems). Some systems, such as [[Smalltalk]] and contemporary versions of [[BASIC]] and [[Java (programming language)|Java]], may also combine two and three types.<ref>Although this scheme (combining strategy 2 and 3) was used to implement certain BASIC interpreters already in the 1970s, such as the efficient BASIC interpreter of the [[ABC 80]], for instance.</ref> Interpreters of various types have also been constructed for many languages traditionally associated with compilation, such as [[ALGOL|Algol]], [[Fortran]], [[COBOL|Cobol]], [[C (programming language)|C]] and [[C++]].

While interpretation and compilation are the two main means by which programming languages are implemented, they are not mutually exclusive, as most interpreting systems also perform some translation work, just like compilers. The terms "[[interpreted language]]" or "[[compiled language]]" signify that the canonical implementation of that language is an interpreter or a compiler, respectively. A [[high-level programming language|high-level language]] is ideally an [[Abstraction (computer science)|abstraction]] independent of particular implementations.