Better error output for parse errors

[kogai]

Implement pretty-printer of parser-error

Input

Type definition which includes invalid syntax

declare v _;

Output

PR Checklist

• [x] Corresponding issue: #43
• [x] Formatted code with refmt
• [x] Ran tests npm test and updated snapshots

[rrdelaney]

This looks great!! Sorry I haven't had the time to review it, but I can get to it this weekend 😄

[rrdelaney]

Rather than doing the error handling + printing in Reason, I think it would be better to return a diagnostic object from compile looking like:

type diagnostic = {.
  "source": string,
  "line": int,
  "col": int
};

and then make compile return:

(string, string, array(diagnostic))

and then the JS code can handle printing and displaying the error.

What do you think?

[kogai]

Sounds great :smile: , let me modify interface :+1: