Restructure code

- Functions accessible in templates are now stored in a separate files
- Functions are documented in Go

functions.go

@@ -0,0 +1,25 @@
+package main
+
+import "os"
+
+var funcMap map[string]any
+
+func init() {
+	funcMap = make(map[string]any)
+	funcMap["file"] = File
+	funcMap["env"] = Env
+}
+
+// File reads a file and returns its content as a string
+func File(name string) string {
+	data, err := os.ReadFile(name)
+	if err != nil {
+		panic(err)
+	}
+	return string(data)
+}
+
+// Env expands environment variables in a string
+func Env(text string) string {
+	return os.ExpandEnv(text)
+}

main.go

@@ -19,19 +19,6 @@ func main() {
 		panic(err)
 	}
 
-	funcMap := make(map[string]any)
-	funcMap["file"] = func(name string) string {
-		data, err := os.ReadFile(name)
-		if err != nil {
-			panic(err)
-		}
-		return string(data)
-	}
-
-	funcMap["env"] = func(text string) string {
-		return os.ExpandEnv(text)
-	}
-
 	tpl := template.Must(
 		template.New(path.Base(tplFile)). //
 							Funcs(funcMap).