June 2018 Update

Task/Left-factorials/Standard-ML/left-factorials.ml

@@ -0,0 +1,29 @@
+(* reuse earlier factorial calculations in dfac, apply to listed arguments in cumlfac *)
+(* example: left factorial n, is #3 (dfac (0,n-1,1,1) ) *)
+(* output list contains (number, factorial, left factorial) *)
+(* tested in PolyML *)
+
+
+val store = ref 0;
+
+val rec dfac = fn
+        (from,to,acc,cm) => if from = to then (from,acc,cm) else (store:=(from+1)*acc;dfac (from+1,to,!store,!store+cm ) );
+
+val rec cumlfac = fn
+        (x::y::rm) => x :: cumlfac ( dfac (#1 x, #1 y, #2 x, #3 x) :: rm ) |
+        rm =>rm ;
+
+val arguments = List.tabulate (10,fn 0=>(0,1,1)|i=>(i,0,0)) @
+                List.tabulate (10,fn i=> (10*i+19,0,0) )    @
+                List.tabulate ( 10,fn i=> (1000*i+999,0,0));
+
+val result = (~1,0,0)::(cumlfac arguments);
+
+(* done *)
+(* display: *)
+
+List.app (fn triple :int*int*int =>
+        print(Int.toString (1+ #1 triple ) ^ " : " ^ Int.fmt StringCvt.DEC (#3 triple ) ^" \n" )
+        ) (List.take(result,21)  ) ;
+List.app (fn triple :int*int*int =>
+        print( Int.toString (1+ #1 triple ) ^ " : " ^ Int.toString  (size(Int.toString (#3 triple ))) ^" \n" ) ) (List.drop(result,21)  );