Unfoldfold

1 definition found

From The Free On-line Dictionary of Computing (27 SEP 03) [foldoc]:

  unfold/fold
       
          A {program transformation} where a {recursive} call to a
          function is {unfold}ed to an instance of the function's body
          and then later an instance of the function's body is replaced
          by a call.  E.g.


       
          	sumdouble l = sum (double l)
       
          	double l = case l of
          	           []   -> []
          		   x:xs -> 2*x + double xs
       
          	==> (unfold double)
       
          	sumdouble l = sum (case l of
          		           []   -> []
          			   x:xs -> 2*x : double xs)
       
          	==> (distribute over case)
       
          	sumdouble l = case l of
          		      []   -> sum []
          		      x:xs -> sum (2*x : double xs)
       
           	==> (unfold sum)
       
          	sumdouble l = case l of
          		      []   -> 0
          		      x:xs -> 2*x + sum (double xs)
       
           	==> (fold sumdouble)
       
          	sumdouble l = case l of
          		      []   -> 0
          		      x:xs -> 2*x + sumdouble xs
       
          (1994-11-03)