Source : Free On-Line Dictionary of Computing

eager evaluation
     
        Any {evaluation strategy} where evaluation of some or all
        function arguments is started before their value is required.
        A typical example is {call-by-value}, where all arguments are
        passed evaluated.  The opposite of eager evaluation is
        {call-by-need} where evaluation of an argument is only started
        when it is required.
     
        The term "{speculative evaluation}" is very close in meaning
        to eager evaluation but is applied mostly to parallel
        architectures whereas eager evaluation is used of both
        sequential and parallel evaluators.
     
        Eager evaluation does not specify exactly when argument
        evaluation takes place - it might be done fully speculatively
        (all {redex}es in the program reduced in parallel) or may be
        done by the caller just before the function is entered.
     
        The term "eager evaluation" was invented by Carl Hewitt and
        Henry Baker  and used in their paper ["The
        Incremental Garbage Collection of Processes", Sigplan Notices,
        Aug 1977.
        {(ftp://ftp.netcom.com/pub/hb/hbaker/Futures.html)}].  It was
        named after their "eager beaver" evaluator.
     
        See also {conservative evaluation}, {lenient evaluation},
        {strict evaluation}.
     
        (1994-12-22)