I've added syntax highlighting to the prompt of my programming language!
It's not strictly necessary, but it's nice to have. It caught a bug with lexing incomplete string literals too.
I'm designing a programming language and trying to decide the type of `let x = 1;`. Should it be Unit or Int?
Advantage of Int: really convenient when evaluating snippets in a REPL.
Advantage of Unit: It's much less confusing when type inference runs on an incomplete function.
Counter-intuitively, if you're writing a parser for a programming language, you need it to be a total function. As soon as you build IDE tooling, you need ASTs from invalid or incomplete input.
The parser should return (Ast, List<Error>) rather than Result<Ast, Error>.