4 files changed, 45 insertions, 5 deletions
diff --git a/const.go b/const.go
new file mode 100644
index 0000000..60bae20
--- /dev/null
+++ b/const.go
@@ -0,0 +1,14 @@
+package main
+
+import "math"
+
+// parseConstant returns nil if s is not a valid constant.
+func parseConstant(s string) *float64 {
+	switch s {
+	case "pi":
+		// Assign to variable because can't take address of constant.
+		var pi float64 = math.Pi
+		return &pi
+	}
+	return nil
+}
diff --git a/func.go b/func.go
new file mode 100644
index 0000000..914cb61
--- /dev/null
+++ b/func.go
@@ -0,0 +1,18 @@
+package main
+
+import "math"
+
+// parseFunction returns nil is s is not a valid function.
+func parseFunction(s string) func(Stack) {
+	switch s {
+	case "sin":
+		return sin
+	}
+	return nil
+}
+
+func sin(stack Stack) {
+	if len(stack) > 0 {
+		stack[len(stack)-1] = math.Sin(stack[len(stack)-1])
+	}
+}
diff --git a/main.go b/main.go
index 0a84c8f..78f4665 100644
--- a/main.go
+++ b/main.go
@@ -7,14 +7,12 @@ import (
 	"github.com/charmbracelet/bubbletea"
 )
 
-// Types
-
 type Calculator struct {
-	stack  []float64
+	stack  Stack
 	buffer string
 }
 
-// Function Definitions
+type Stack []float64
 
 func main() {
 	if _, err := tea.NewProgram(new(UI)).Run(); err != nil {
diff --git a/ui.go b/ui.go
index 2768c43..886b4c3 100644
--- a/ui.go
+++ b/ui.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"strconv"
 
 	"github.com/charmbracelet/bubbletea"
 )
@@ -40,6 +41,15 @@ func (ui UI) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			if len(ui.calc.buffer) > 0 {
 				ui.calc.buffer = ui.calc.buffer[:len(ui.calc.buffer)-1]
 			}
+		case "enter":
+			if fn := parseFunction(ui.calc.buffer); fn != nil {
+				fn(ui.calc.stack)
+			} else if con := parseConstant(ui.calc.buffer); con != nil {
+				ui.calc.stack = append(ui.calc.stack, *con)
+			} else if f, err := strconv.ParseFloat(ui.calc.buffer, 64); err != nil {
+				ui.calc.stack = append(ui.calc.stack, f)
+			}
+			ui.calc.buffer = ""
 		default:
 			ui.calc.buffer += msg.String()
 		}
@@ -50,7 +60,7 @@ func (ui UI) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 func (ui UI) View() string {
 	var s string
 	for _, f := range ui.calc.stack {
-		s += fmt.Sprintf("%.*g\n", sigDigs, f)
+		s += fmt.Sprintf(" %.*g\n", sigDigs, f)
 	}
 	s += boxTop(ui.windowWidth) + "\n"
 	s += fmt.Sprintf("%[1]c%-*s%[1]c\n", boxVertical, ui.windowWidth-2, ui.calc.buffer)