error handling and tidying

1 files changed, 28 insertions, 15 deletions

diff --git a/func.go b/func.go
index 42763c0..c64e97a 100644
--- a/func.go
+++ b/func.go
@@ -73,32 +73,29 @@ func invTrig(fn string) func(Calculator) {
 
 // Convert radians to degrees.
 func deg(c Calculator) {
-	if len(c.stack) > 0 {
-		c.stack[len(c.stack)-1] = degrees(c.stack[len(c.stack)-1])
+	if n, err := c.stack.pop(); err == nil {
+		c.stack.push(degrees(n))
 	}
 }
 
 // Convert degrees to radians.
 func rad(c Calculator) {
-	if len(c.stack) > 0 {
-		c.stack[len(c.stack)-1] = radians(c.stack[len(c.stack)-1])
+	if n, err := c.stack.pop(); err == nil {
+		c.stack.push(radians(n))
 	}
 }
 
 // Factorial (!).
 func fac(c Calculator) {
-	if len(c.stack) > 0 {
-		a := &c.stack[len(c.stack)-1] // will replace with a!
-		if float64(int(*a)) != *a {   // undefined on non-ints
-			return
-		} else if int(*a) == 0 { // 0! = 1
-			*a = 1.0
-		} else { // a! = a*(a-1)!
-			for i := int(*a) - 1; i > 1; i-- {
-				*a *= float64(i)
-			}
-		}
+	n, err := c.stack.pop()
+	if err != nil {
+		return
+	}
+	if !isUint(n) { // undefined on non-ints
+		c.stack.push(n)
+		return
 	}
+	c.stack.push(float64(factorial(uint(n))))
 }
 
 // radians converts degrees to radians.
@@ -110,3 +107,19 @@ func radians(deg float64) float64 {
 func degrees(rad float64) float64 {
 	return rad * 180 / math.Pi
 }
+
+// factorial returns n! (n factorial).
+func factorial(n uint) uint {
+	if n == 0 { // 0! = 1
+		return 1
+	}
+	// n! = n*(n-1)!
+	for i := n - 1; i > 1; i-- {
+		n *= i
+	}
+	return n
+}
+
+func isUint(n float64) bool {
+	return float64(uint(n)) == n
+}