Comment by clark800

Looks very similar to lambda zero syntax (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.