Source : Free On-Line Dictionary of Computing

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,
        {cluster}s 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 conversion}s.  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}.
     
        {Exception}s 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 variable}s 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 .
     
        {Versions for Sun and VAX/VMS
        (ftp://pion.lcs.mit.edu/pub/clu/)}.  {Portable version
        (ftp://mintaka.lcs.mit.edu/pub/dcurtis/)}.
     
        (1994-12-16)