add: calculator example to x-tba

x-tba/foundations/calc/09-packages/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/inancgumus/learngo/x-tba/foundations/calc/09-packages/calc"
+)
+
+func main() {
+	// lesson: packaging
+
+	// separate dependencies like getting and validating
+	// user data as in here.
+	//
+	// we only put calc to another packages, not the other
+	// stuff.
+	//
+	// so, we can reuse the same calc package and use it
+	// over a web api if we want.
+
+	if len(os.Args) != 4 {
+		fmt.Println("Usage: calc <number1> <operator> <number2>")
+		return
+	}
+
+	var (
+		a, b float64
+		err  error
+	)
+
+	if a, err = calc.Parse(os.Args[1]); err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	if b, err = calc.Parse(os.Args[3]); err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	op := os.Args[2]
+	res, err := calc.Do(a, b, op)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	fmt.Printf("%v %s %v = %v\n", a, op, b, res)
+}