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.
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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.
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>.
It's surprisingly fiddly to parse unfinished multiline expressions in a REPL.
In Garden, my toy language, the parser distinguishes 'incomplete' from other others, so I can keep appending text and re-parsing until something useful comes out.
