资料来源 : Free On-Line Dictionary of Computing

let floating
     
         A {program transformation} used in {functional
        programming} to implement {full laziness}.  E.g. the function
     
        	f x = x + sqrt 4
     
        can be expressed as
     
        	f x = let t = sqrt 4 in x + t
     
        but note that t does not depend on the argument x so we can
        automatically transform this to
     
        	t = sqrt 4
        	f x = x + t
     
        Making t into a global constant which need only be evaluated
        at most once, rather than every time f is called.  The general
        idea is to float each subexpression as far out (toward the
        top level) as possible to maximise sharing.
     
        (1997-07-09)