Looks very similar to lambda zero syntax (https://github.com/clark800/lambda-zero https://github.com/clark800/lambda-zero): def getNaturalName(tag, globals

Looks very similar to lambda zero syntax (https://github.com/clark800/lambda-zero https://github.com/clark800/lambda-zero): def getNaturalName(tag, globals) if globals.lookup("0") is Just(Global(_, _, term)) if term is Numeral(_, type, _) return Just(Name(getTermTag(type))) error showSyntaxError("0 must be a numeral to use numerals", tag) return Void Though this ultimate conditional syntax is more general because lambda zero only allows one destructuring per conditional to simplify parsing.