trig functions

1 files changed, 41 insertions, 9 deletions

diff --git a/func.go b/func.go
index 914cb61..445cb41 100644
--- a/func.go
+++ b/func.go
@@ -1,18 +1,50 @@
 package main
 
-import "math"
+import (
+	"fmt"
+	"math"
+)
 
-// parseFunction returns nil is s is not a valid function.
-func parseFunction(s string) func(Stack) {
-	switch s {
-	case "sin":
-		return sin
+// parseFunction returns nil is fn is not a valid function.
+func parseFunction(fn string) func(Calculator) {
+	switch fn {
+	case "sin", "cos", "tan":
+		return trig(fn)
 	}
 	return nil
 }
 
-func sin(stack Stack) {
-	if len(stack) > 0 {
-		stack[len(stack)-1] = math.Sin(stack[len(stack)-1])
+// trig returns a closure that performs the trig function specified by fn.
+// Panics if fn is not one of "sin", "cos" or "tan".
+func trig(fn string) func(Calculator) {
+	return func(c Calculator) {
+		if len(c.stack) <= 0 {
+			return
+		}
+		v := &c.stack[len(c.stack)-1]
+		// The math package expects arguments to trig functions to be in radians.
+		if c.anglem == modeDeg {
+			*v = radians(*v)
+		}
+		switch fn {
+		case "sin":
+			*v = math.Sin(*v)
+		case "cos":
+			*v = math.Cos(*v)
+		case "tan":
+			*v = math.Tan(*v)
+		default:
+			panic(fmt.Sprintf("invalid trig function: '%s'", fn))
+		}
 	}
 }
+
+// radians converts degrees to radians.
+func radians(deg float64) float64 {
+	return deg * math.Pi / 180.0
+}
+
+// degrees converts radians to degrees.
+func degrees(rad float64) float64 {
+	return rad * 180 / math.Pi
+}