From 008e4021375883610cf1b07e005a4176acadc0de Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 29 Jul 2023 11:19:55 -0230
Subject: trig functions

---
 calc.go | 12 ++++++++++--
 func.go | 50 +++++++++++++++++++++++++++++++++++++++++---------
 ui.go   |  2 +-
 3 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/calc.go b/calc.go
index 8afc43a..1d969cc 100644
--- a/calc.go
+++ b/calc.go
@@ -5,9 +5,17 @@ import (
 	"strings"
 )
 
+type AngleMode int
+
+const (
+	modeDeg = iota
+	modeRad
+)
+
 type Calculator struct {
-	stack Stack
-	buf   string
+	stack  Stack
+	buf    string
+	anglem AngleMode
 }
 
 // swap swaps the values of the buffer and the bottom element of the stack. If
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
+}
diff --git a/ui.go b/ui.go
index 9bf9caa..877f11b 100644
--- a/ui.go
+++ b/ui.go
@@ -56,7 +56,7 @@ func (ui UI) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			}
 		case "enter":
 			if fn := parseFunction(ui.calc.buf); fn != nil {
-				fn(ui.calc.stack)
+				fn(ui.calc)
 			} else if con := parseConstant(ui.calc.buf); con != nil {
 				ui.calc.stack.push(*con)
 			} else if f, err := strconv.ParseFloat(ui.calc.buf, 64); err == nil {
-- 
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