simplify the code, and invert Result and Option

src/bin/dicebot-cmd.rs

@@ -3,9 +3,9 @@ use axfive_matrix_dicebot::commands::parse_command;
 fn main() -> Result<(), String> {
     let command = std::env::args().skip(1).collect::<Vec<String>>().join(" ");
     let command = match parse_command(&command) {
-        Some(Ok(command)) => command,
-        Some(Err(e)) => return Err(format!("Error parsing command: {}", e)),
-        None => return Err("Command not recognized".into()),
+        Ok(Some(command)) => command,
+        Ok(None) => return Err("Command not recognized".into()),
+        Err(e) => return Err(format!("Error parsing command: {}", e)),
     };
     println!("{}", command.execute().plain());
     Ok(())

src/commands.rs

@@ -36,11 +36,10 @@ impl Command for RollCommand {
     }
 }
 
-pub fn parse_command(s: &str) -> Option<Result<Box<dyn Command>, String>> {
+pub fn parse_command(s: &str) -> Result<Option<Box<dyn Command>>, String> {
     // Ignore trailing input, if any.
     match parser::parse_command(s) {
-        Ok((_, Some(command))) => Some(Ok(command)),
-        Ok((_, None)) => None,
-        Err(err) => Some(Err(err.to_string())),
+        Ok((_, result)) => Ok(result),
+        Err(err) => Err(err.to_string()),
     }
 }