Unified error terms and text

[gomoripeti]

It would be good to have an option to return errors as erlang terms (when called from Erlang, not cli).

• various frontends can format the errors according to their taste (eg Elixir syntax formatting).
• also testing negative cases could be more precise

This requires unifying and documenting the error terms, each one having the same structure (common fields in same position: eg filename, line number, expected type etc.)

Also the default formatter (used by the cli) could have a format similar to other tools, like the compiler: file-name:line-number:error-text

[zuiderkwast]

For a type error on the form of an expression E not matching a type T, I suggest the simple structure {type_error, E, T} where E and T are abstract syntax. Line number can be extracted from E. This would cover many of the currently different type errors.

[Zalastax]

@josefs can we get your blessing to make this happen? I expect that I can dish out a PR addressing this issue before the week ends if we can agree on the format.

[zuiderkwast]

I can answer yes on this question. Almost certain that Josef doesn't mind that you sort this out!

[josefs]

@Zalastax, go wild! I'd love to see this happen.