Yes, pardon my quick typing.
More specifically, a case constant is not a _constant pattern_ (at
least, not yet), it is just a constant case label. Constants are typed,
and they carray both a type match and a value match. When you say
case 0
this is a constant for an int, and doesn't match a floating point zero
(if the match target is `float`, it won't even compile.) Similarly,
`case 0.0` is a constant for a float, and is not applicable to a match
target of int. (We do have the usual tolerance for matching int
constants to shorter int types, as before.)
We may generalize these to constant patterns in the future, but right
now, these are constant case labels and their semantics are derived from
that of existing case labels.
On 1/26/2023 10:25 AM, Guy Steele wrote:
On Jan 26, 2023, at 9:36 AM, Brian Goetz <[email protected]> wrote:
...
For comparing a variable to a constant, representational equality is
the obvious interpretation; `case nnn` means "is it the number nnn".
This allows you to say `case NaN` and `case -0` and get the right
answer (all of these relations agree on what to do about 1.0).
Careful: I think you had better say “case -0.0”; otherwise the
constant expression “-0” will be reduced to “0” and only then
converted to floating-point representation, producing +0.0.
Yes, floating-point is VERY fiddly.
—Guy
