One of the many things that I admire about Elm as a programming language is the quality of the compiler’s error messages.  The “hooks” for providing good error messages are provided by the Error data structure in the elm-tools/parser package.  The goal, then, is to make MiniLatex producs as informative and helpful as does Elm.  This work is just beginning, but here is a sample of what is possible:

To do this, I’ve added the type LXError Error to the alternatives that make up the LatexExpression type used by the parser — a recursive type that represents the abstract syntax tree.  The Error type, which comes from the elm-tools parser, looks like this:

type alias Error = {
     row : Int
   , col : Int
   , source : String
   , problem : Problem
   , context : List Context
 }

It gives enough information so with a suitable dictionary of error data and a bit of logic one can return good error messages.  The challenge now is to collect and analyze errors, then wire this kind of intelligence in to MiniLatex.

I’ve implemented only a few error messages as of this writing, but you can experiment with the MiniLatex Demo App.