Add --action option to not executable

* --action dump, parse, or run will cause the program to do the
  appropriate action.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/bin/not.rs

@@ -18,11 +18,20 @@ struct Options {
     #[structopt(short = "d", long)]
     disassemble: bool,
     */
+
+    #[structopt(long, default_value = "run")]
+    action: String,
 }
 
 fn main() -> Result<()> {
     let opt = Options::from_args();
     let text = fs::read_to_string(&opt.input)?;
+    let action = &opt.action.to_lowercase();
+    match action.as_str() {
+        "run" | "parse" | "dump" => {},
+        _ => eprintln!("WARNING: unknown action {}", action)
+    }
+
     let ast = match ast::parse(text.as_str()) {
         Ok(ast) => ast,
         Err(errs) => {
@@ -32,15 +41,17 @@ fn main() -> Result<()> {
             return Err("errors reported, exiting".into());
         }
     }.unwrap();
-    //println!("{:#?}", ast);
+    if action == "parse" {
+        println!("{:#?}", ast);
+        return Ok(());
+    }
 
     let package = Compile::new().compile(&ast)?;
 
-    //println!("{:#?}", inst);
-    //println!("{:#?}", const_pool);
-    {
+    if action == "dump" {
         let mut stdout = std::io::stdout();
         package.dump(&mut stdout)?;
+        return Ok(());
     }
 
     Ok(())