Correction - failure of either-ref does take arguments.    But 'raise' only works if Left has only one argument (and although you usually store some kind of mssage there, it doesn't look very useful to raise that message alone---but that's a different story.)

On Wed, Jun 3, 2020 at 6:47 PM Shiro Kawai <> wrote:
It says the default value of failure is 'raise', but 'raise' needs to take one argument, while the failure procedure is called with no argument.
The reference implementation defaults failure to be (lambda () (raise (maybe-ref-error))).