Ousterhout's dichotomy

language John Ousterhout's division of high-levellanguages into "system programming languages" and "scripting

languages". This distinction underlies the design of his

language Tcl.

System programming languages (or "applications languages") are

strongly typed, allow arbitrarily complex data structures,

and programs in them are compiled, and are meant to operate

largely independently of other programs. Prototypical system

programming languages are C and Modula-2.

By contrast, scripting languages (or "glue languages") are

weakly typed or untyped, have little or no provision for

complex data structures, and programs in them ("scripts")

are interpreted. Scripts need to interact either with other

programs (often as glue) or with a set of functions provided

by the interpreter, as with the file system functions

provided in a UNIX shell and with Tcl's GUI functions.

Prototypical scripting languages are AppleScript, C Shell,

MSDOS batch files, and Tcl.

Many believe that this is a highly arbitrary dichotomy, and

refer to it as "Ousterhout's fallacy" or "Ousterhout's false

dichotomy". While strong-versus-weak typing, data structure

complexity, and independent versus stand-alone might be said

to be unrelated features, the usual critique of Ousterhout's

dichotomy is of its distinction of compilation versus

interpretation, since neither semantics nor syntax depend

significantly on whether code is compiled into

machine-language, interpreted, tokenized, or

byte-compiled at the start of each run, or any mixture of

these. Many languages fall between being interpreted or

compiled (e.g. Lisp, Forth, UCSD Pascal, Perl, and

Java). This makes compilation versus interpretation a

dubious parameter in a taxonomy of programming languages.

(2002-05-28)