add chapter 15.7 (#683)

eBook/examples/chapter_15/template_variables.go

@@ -0,0 +1,25 @@
+// template_variables.go
+package main
+
+import (
+	"os"
+	"text/template"
+)
+
+func main() {
+	t := template.New("test")
+	t = template.Must(t.Parse("{{with $3 := `hello`}}{{$3}}{{end}}!\n"))
+	t.Execute(os.Stdout, nil)
+
+	t = template.Must(t.Parse("{{with $x3 := `hola`}}{{$x3}}{{end}}!\n"))
+	t.Execute(os.Stdout, nil)
+
+	t = template.Must(t.Parse("{{with $x_1 := `hey`}}{{$x_1}} {{.}} {{$x_1}}{{end}}!\n"))
+	t.Execute(os.Stdout, nil)
+}
+
+/* Output:
+hello!
+hola!
+hey hey hey!
+*/