Completed hw7 excersizes 1 and 2

sml_ruby/hw7.sml

@@ -19,6 +19,7 @@ datatype geom_exp =
 	 | Intersect of geom_exp * geom_exp (* intersection expression *)
 	 | Let of string * geom_exp * geom_exp (* let s = e1 in e2 *)
 	 | Var of string
+	 | Shift of real * real * geom_exp
 (* CHANGE add shifts for expressions of the form Shift(deltaX, deltaY, exp *)
 
 exception BadProgram of string
@@ -181,6 +182,15 @@ fun intersect (v1,v2) =
          * line segments are not actually points (endpoints not real close)
          * lines segment have left (or, if vertical, bottom) coordinate first
 *)
+fun reposition (deltaX,deltaY,e) =
+    case e of
+	NoPoints => e (* first 5 cases are all values, so no computation *)
+      | Point (x,y)  => Point(x+deltaX,y+deltaY)
+      | Line (m,b)  => Line (m,(b+deltaY)-(m*deltaX))
+      | VerticalLine x => VerticalLine (x+deltaX)
+      | LineSegment (x1,y1,x2,y2)  => LineSegment (x1+deltaX,y1+deltaY,x2+deltaX,y2+deltaY)
+
+
 
 fun eval_prog (e,env) =
     case e of
@@ -190,11 +200,31 @@ fun eval_prog (e,env) =
       | VerticalLine _ => e
       | LineSegment _  => e
       | Var s => 
-	(case List.find (fn (s2,v) => s=s2) env of
-	     NONE => raise BadProgram("var not found: " ^ s)
-	   | SOME (_,v) => v)
+				(case List.find (fn (s2,v) => s=s2) env of
+				     NONE => raise BadProgram("var not found: " ^ s)
+				   | SOME (_,v) => v)
       | Let(s,e1,e2) => eval_prog (e2, ((s, eval_prog(e1,env)) :: env))
       | Intersect(e1,e2) => intersect(eval_prog(e1,env), eval_prog(e2, env))
+
 (* CHANGE: Add a case for Shift expressions *)
+	  | Shift(deltaX,deltaY,e) => 
+	              (case e of
+				     Var s => reposition (deltaX,deltaY,eval_prog(e,env))
+				   | _ => reposition (deltaX,deltaY,e))
+
 
 (* CHANGE: Add function preprocess_prog of type geom_exp -> geom_exp *)
+fun preprocess_prog (e) =
+	    case e of
+	NoPoints => e 
+      | Point _  => e
+      | Line _   => e
+      | VerticalLine _ => e
+      | LineSegment(x1,y1,x2,y2)  => 
+      		if real_close_point (x1,y1) (x2,y2)
+      		then Point (x1,y1)
+      		else if x1 <= x2 andalso y1 <= y2
+      			 then e
+      			 else LineSegment(x2,y2,x1,y1)
+      | Var s => e
+      | Shift(deltaX,deltaY,e) => reposition (deltaX,deltaY,e)