Refactor evaluator into eval func

inp.txt

@@ -1 +1 @@
-pH pe pl pl po p, pW po pr pl pd p!
+pHello pWorld!

src/main.rs

@@ -23,18 +23,23 @@ impl Program {
         return Program{ data: op_list, pc: 0 };
     }
 
+    fn eval(&self, instruction: &String) {
+        let instruction_vec: Vec<char> = instruction.chars().collect();
+        let opcode = instruction_vec[0];
+        let arguments = &instruction[1..];
+
+        match opcode {
+            'p' => println!("{}", arguments),
+            _ => panic!("SyntaxError at opcode {}!", self.pc)
+        }
+    }
+
     fn run(&mut self) {
         println!("{}", self);
         while self.pc < self.data.len() {
             let instruction = &self.data[self.pc];
-            let instruction_vec: Vec<char> = instruction.chars().collect();
-            let opcode = instruction_vec[0];
-
-            match opcode {
-                'p' => print!("{}", instruction_vec[1]),
-                _ => panic!("SyntaxError at opcode {}!", self.pc)
-            }
 
+            self.eval(instruction);
 
             self.pc = self.pc + 1;
         }