Ousterhout's dichotomy

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Ousterhout's dichotomy is John Ousterhout's claim^[1] that high-level languages tend to fall into two groups, each with distinct properties and uses: "system programming languages" and "scripting languages". This distinction underlies the design of his language Tcl.

System programming languages (or "applications languages") usually have the following properties:

They are statically typed
They support the creation of complex data structures
Programs in them are compiled into machine code

System programming languages tend to be used for components and applications with large amounts of internal functionality such as operating systems, database servers, and Web browsers. These applications typically employ complex algorithms and data structures and require high performance. Popular system programming languages include C, C++, and Pascal.

By contrast, scripting languages (or "glue languages") tend to have the following properties:

They are dynamically typed
They have little or no provision for complex data structures
Programs in them ("scripts") are interpreted directly, or compiled into bytecode or a parse tree

Scripting languages tend to be used for applications where most of the functionality comes from other programs (often implemented in system programming languages); the scripts are used to "glue" together other programs or add additional layers of functionality on top of existing programs. Scripts tend to be short and are often written by less sophisticated programmers, so execution efficiency is less important than simplicity and ease of interaction with other programs. Common applications for scripting include Web page generation, report generation, graphical user interfaces, and system administration. Popular scripting languages include AppleScript, C Shell, DOS batch files, Perl, Tcl,Windows PowerShell, and Python.