Hi John and the SRFI 249 ml,

Should an implementation of SRFI 249 maintain some kind of order
among the ambient restarters? In particular, do we care whether
'with-restarters' reorders the result of '(ambient-restarters)'? The
spec says that 'with-restarters' "establishes restarters ... as
ambient restarters *on top of* the existing ambient restarters"
(emphasis mine). Should this be understood to mean that the following
returns '(b a ...)' (where ... refers to any already-established
ambient restarters)?

    (define rA (make-restarter 'a '("restarter A") values))
    (define rB (make-restarter 'b '("restarter B") values))

    (with-restarters
     rA
     (lambda ()
       (with-restarters
        rB
        (lambda ()
          (map restarter-tag (ambient-restarters))))))

At the moment, the tests assume that, if there are no prior ambient
restarters, either '(b a)' or '(a b)' is a valid result here.

It would simplify things to make "the ambient restarters" a list,
and to make '(with-restarters restarters thunk)' equivalent to

    (parameterize ((ambient-restarters
                    (collect-restarters restarters)))
      (thunk))

since 'collect-restarters' has clear-ish priority semantics. But this
would break other implementations that might conform to the SRFI.
What if we want to store the ambient restarters in a bag, and have
'ambient-restarters' project that bag to a list in unspecified order?

It's also possible to get several ambient restarters with the
same tag using these nested 'with-restarters' expressions,
since 'w.-r.' doesn't check its *restarters* argument against
'(ambient-restarters)':

    (define rA (make-restarter 'a '("foo") values))
    (define rA* (make-restarter 'a '("bar") values))

    (with-restarters
     rA
     (lambda ()
       (with-restarters
        rA*
        (lambda ()
          (list
           (map restarter-tag (ambient-restarters)))))))

     => (a a ...) [or (... a ... a ...)?]

I'm not sure if this is important.

I also think that "Returns the current list of ambient restarters"
in the 'ambient-restarters' spec should be changed to "Returns a
list of the current ambient restarters". The list can be
ephemeral--right?

Regards,

Wolf

--
Wolfgang Corcoran-Mathe  <xxxxxx@sigwinch.xyz>