Source : WordNet®

evaluator
     n : an authority who is able to estimate worth or quality [syn:
         {judge}]

Source : Free On-Line Dictionary of Computing

evaluator
     
         Geoff Burn defines evaluators E0, E1, E2 and E3 which
        when applied to an expression, reduce it to varying degrees.
        E0 does no evaluation, E1 it evaluates to {weak head normal
        form} (WHNF), E2 evaluates the structure of a list, i.e. it
        evaluates it either to NIL or evaluates it to a CONS and then
        applies E2 to the second argument of the CONS.  E3 evaluates
        the structure of a list and evaluates each element of the list
        to {WHNF}.  This concept can be extended to data structures
        other than lists and forms the basis of the {evaluation
        transformer} style of {strictness analysis}.
     
        (1994-12-12)