資料來源 : Free On-Line Dictionary of Computing

graph reduction
     
        A technique invented by Chris Wadsworth where an expression is
        represented as a {directed graph} (usually drawn as an
        inverted tree).  Each node represents a function call and its
        subtrees represent the arguments to that function.  Subtrees
        are replaced by the expansion or value of the expression they
        represent.  This is repeated until the tree has been reduced
        to a value with no more function calls (a {normal form}).
     
        In contrast to {string reduction}, graph reduction has the
        advantage that common subexpressions are represented as
        pointers to a single instance of the expression which is only
        reduced once.  It is the most commonly used technique for
        implementing {lazy evaluation}.