eval: started implementing binary operations

src/main.rs

@@ -80,6 +80,19 @@ fn parse(contents: String, opcodes: HashMap<&'static str, (i64, i32)>) -> Vec<i6
     return code
 }
 
+fn binop<F>(stack: &mut Vec<i64>, fun: F) where F: Fn(i64, i64) -> i64 {
+    let x = stack.pop();
+    let y = stack.pop();
+    match x {
+        Some(x) =>
+            match y {
+                Some(y) => stack.push(fun(x, y)),
+                _       => panic!("pop needs at least two elements on the stack")
+            },
+        _       => panic!("pop needs at least two elements on the stack")
+    }
+}
+
 fn exec(instructions: Vec<i64>) -> i64 {
     let mut stack: Vec<i64> = Vec::new();
     let ilen = instructions.len();
@@ -88,10 +101,10 @@ fn exec(instructions: Vec<i64>) -> i64 {
         ip += 1; /* TMP */
         match instructions[ip] {
             /* ENT */ 0 => (),
-            /* ADD */ 1 => (),
-            /* SUB */ 2 => (),
-            /* MUL */ 3 => (),
-            /* DIV */ 4 => (),
+            /* ADD */ 1 => binop(&mut stack, |x, y| x + y),
+            /* SUB */ 2 => binop(&mut stack, |x, y| x - y),
+            /* MUL */ 3 => binop(&mut stack, |x, y| x * y),
+            /* DIV */ 4 => binop(&mut stack, |x, y| x / y),
             /* MOD */ 5 => (),
             /* LT  */ 6 => (),
             /* EQ  */ 7 => (),