diff --git a/src/rpn.rs b/src/rpn.rs
index d1cd3c3..6907772 100644
--- a/src/rpn.rs
+++ b/src/rpn.rs
@@ -138,6 +138,33 @@ fn err<T: StrError>(argv0: &String, e: &T, code: Option<u8>) -> ExitCode {
 	ExitCode::from(code.unwrap_or(1 /* unknown error */))
 }
 
+fn operate(
+	mut stack: VecDeque<f64>,
+	op: CalcType,
+) -> Result<VecDeque<f64>, EvaluationError> {
+	let vals = (stack.pop_back(), stack.pop_back());
+
+	if let (Some(x), Some(y)) = vals {
+		match op {
+			Add => stack.push_back(y + x),
+			Subtract => stack.push_back(y - x),
+			Multiply => stack.push_back(y * x),
+			Divide => stack.push_back(y / x),
+			Power => stack.push_back(y.powf(x)),
+			Floor => stack.push_back((y / x).floor()),
+			Modulo => stack.push_back(y % x),
+			_ => {},
+		};
+	} else {
+		return Err(EvaluationError {
+			message: format!("{}: unexpected operation", op),
+			code: EX_DATAERR,
+		})
+	}
+
+	Ok(stack)
+}
+
 fn eval(
 	input: &str,
 	initial_stack: VecDeque<f64>,
@@ -170,27 +197,9 @@ fn eval(
 			},
 			op => {
 				ops.push_back(op.clone());
+
 				oper = true; /* this is an operation */
-
-				let vals = (stack.pop_back(), stack.pop_back());
-
-				if let (Some(x), Some(y)) = vals {
-					match op {
-						Add => stack.push_back(y + x),
-						Subtract => stack.push_back(y - x),
-						Multiply => stack.push_back(y * x),
-						Divide => stack.push_back(y / x),
-						Power => stack.push_back(y.powf(x)),
-						Floor => stack.push_back((y / x).floor()),
-						Modulo => stack.push_back(y % x),
-						_ => {},
-					};
-				} else {
-					return Err(EvaluationError {
-						message: format!("{}: unexpected operation", op),
-						code: EX_DATAERR,
-					})
-				}
+				return operate(stack, op).map(|s| (s, oper));
 			},
 		};
 	}