fn unary_leaf_expr(&mut self, token: Token) -> WeldResult<Box<Expr>> {
        self.consume(TOpenParen)?;
        let value = self.expr()?;
        self.consume(TCloseParen)?;
        let kind = self.unary_op_kind_for_token(token)?;
        Ok(expr_box(UnaryOp { kind, value }, Annotations::new()))
    }
Helper function for leaf_expr as all functions with unary args follow same pattern.
weld/src/syntax/parser.rs