CLU

CLUster.

An object-oriented programming language developed at MIT

by Liskov et al in 1974-1975.

CLU is an object-oriented language of the Pascal family

designed to support data abstraction, similar to Alphard.

It introduced the iterator: a coroutine yielding the

elements of a data object, to be used as the sequence of

values in a 'for' loop.

A CLU program consists of separately compilable procedures,

clusters and iterators, no nesting. A cluster is a module

naming an abstract type and its operations, its internal

representation and implementation. Clusters and iterators may

be generic. Supplying actual constant values for the

parameters instantiates the module.

There are no implicit type conversions. In a cluster, the

explicit type conversions 'up' and 'down' change between the

abstract type and the representation. There is a universal

type 'any', and a procedure force[] to check that an object is

a certain type. Objects may be mutable or immutable.

Exceptions are raised using 'signal' and handled with

'except'. Assignment is by sharing, similar to the sharing

of data objects in Lisp. Arguments are passed by

call-by-sharing, similar to call-by-value, except that the

arguments are objects and can be changed only if they are

mutable. CLU has own variables and multiple assignment.

See also Kamin's interpreters, clu2c.

["CLU Reference Manual", Barbara Liskov et al, LNCS 114,

Springer 1981].

E-mail: Paul R. Johnson [email protected].

Versions for Sun and VAX/VMS. Portable version.

(1994-12-16)