Finished required sections of assignment, including comments.

Homework_1.sml

@@ -2,38 +2,54 @@
 	Homework 1: Simple Register Machine
 	By: Ashley Sanders
 *)
+
+(*Used to store the values of the two registers: a and b*)
 type MachineState = {a:int, b:int};
+
+(*May contain the value of any defined instruction*)
+datatype Instruction = SetA of int | SetB of int | Add | Sub | Disp;
+
+(*Creates a new MachineState with the given initial values*)
 fun newMachine (a, b) : MachineState = {a=a, b=b};
 
-(*Getters and Setters*)
+(*Gets the current value of a in the given MachineState*)
 fun getA (m : MachineState) = #a m;
+
+(*Gets the current value of b in the given MachineState*)
 fun getB (m : MachineState) = #b m;
+
+(*Sets the value of a in the given MachineState*)
 fun setA (m : MachineState, newA) = newMachine(newA, #b m);
+
+(*Sets the value of b in the given MachineState*)
 fun setB (m : MachineState, newB) = newMachine(#a m, newB);
 
-datatype Instruction = SetA of int | SetB of int | Add | Sub | Disp;
-(*Converts Instruction to a string*)
+(*Converts an Instruction to a string for ease of printing values*)
 fun i2s (SetA a)	= "SetA " ^ Int.toString(a)
 	| i2s (SetB b)	= "SetB " ^ Int.toString(b)
 	| i2s Add		= "Add"
 	| i2s Sub		= "Sub"
 	| i2s Disp		= "Disp";
 
-(*Evaluates the given Instruction*)
-fun eval (m: MachineState, SetA a)	: MachineState = m;
-	| eval (m: MachineState, SetB b): MachineState = m;
-	| eval (m: MachineState, Add)	: MachineState = m;
-	| eval (m: MachineState, Sub)	: MachineState = m;
+(*Evaluates the given Instruction based on the given MachineState*)
+fun eval (m: MachineState, SetA a)	: MachineState = 
+		(setA (m, a))
+	| eval (m: MachineState, SetB b): MachineState = 
+		(setB (m, b))
+	| eval (m: MachineState, Add)	: MachineState = 
+		(newMachine(getA (m) + getB (m), getB (m)))
+	| eval (m: MachineState, Sub)	: MachineState = 
+		(newMachine(getA (m) - getB (m), getB (m)))
 	| eval (m: MachineState, Disp)	: MachineState = 
 		(print (Int.toString (#a m) ^ "\n"); m);
 
-(*Runs the list of Instructions*)
+(*Runs and prints the given list of Instructions*)
 fun run (m: MachineState, []: Instruction list) = m
 	| run (m: MachineState, prog: Instruction list) =
 		let val instr = hd prog
 			val instrs = tl prog
 			val _ = print (i2s instr ^ "\n");
 			val m1 = eval (m, instr);
-		in print (i2s instr ^ "\n");
+		in 
 			run (m1: MachineState, tl prog : Instruction list)
 		end;