On 28.01.2010, at 10:00, Meikel Brandmeyer wrote:
On Jan 28, 8:56 am, Konrad Hinsen <[email protected]> wrote:
Perhaps m-result in maybe-m should throw an exception if the value
passed in is nil, to enforce this rule.
I would vote for using ::nothing or the like for that purpose and
allow nil as value. I don't think the monad should care what the
payload is.
If you use (maybe-t identity-m) instead of maybe-m, you can actually
specify your own "nothing" value as an optional argument, e.g. (maybe-
t identity-m ::nothing).
The maybe-m monad is a constant monad, so an optional parameter is not
possible. After considering something like ::nothing, I finally
settled for nil as a default "nothing" value because this is the most
convenient choice in most settings. In particular, it makes it
possible to use when forms as convenient generators of maybe-m values.
Konrad.
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