Comment by thenewwazoo

Because I'm on my soapbox, I'll also recommend implementing ToString[1] right off the bat, too. That way you can print out useful error messages immediately.

For example, if your errors are:

  enum RispError {
      /// Syntax error returning line number and char
      SyntaxErr(u32, u32),
      /// Parens not balanced; contains number of parens needed
      UnbalancedParens(usize),
  }

You can impl ToString straight away:

  impl ToString for RispErr {
      fn to_string(&self) -> String {
          match self {
              RispErr::SyntaxErr(l,c) => format!("syntax error at line {}, col {}", l, c),
              RispErr::UnbalancedParens(n) => format!("use your % key more! add {} more paren", n),
          }
      }
  }

Then, when handling the error, you can

  match do_thing() {
      Ok(v) => { ... },
      Err(e) => { // TODO handle error
          println!(e)
      }
  }

where do_thing's signature looks like

  fn do_thing(...) -> Result<T, RispErr>;

It takes the same amount of code, but all your error messages are in the same place, you haven't lost information about them, and refactoring to handle them becomes super easy.

(n.b. I dashed this comment off without actually compiling the above, so please forgive any dumb errors =] )

[1] https://doc.rust-lang.org/std/string/trait.ToString.html