> Earlier e-mail example:
>> let foo =
>> "positive" where ( bar > 0 ) ??
>> "negative" where ( bar < 0 ) ??
>> "zero"
>
> let foo = bar > 0 ? "positive" :
> bar < 0 ? "negative" :
> "zero"
See, this just makes me want to remix ternary...
let foo = (bar > 0) :: "positive" ??
(bar < 0) :: "negative" ??
"zero"
// :: is not actually legal to declare, but notionally...
infix operator :: {
associativity left
precedence 133
}
func :: <B: BooleanType, T>(lhs: B, rhs: @autoclosure () -> T?) -> T? {
guard lhs else {
return nil
}
return rhs()
}
`::` is an operator which evaluates the condition on the left and returns the
right if true, or nil otherwise. You can chain `::`s together with the existing
`??` operator. You can terminate the sequence with a trailing `?? value` to
ensure you won't get a nil. Or you can leave off the trailing `??`, or even
omit the chain of `??`s altogether if `::` by itself does what your code needs.
Actually, the main problem I see here is that `??`'s, and therefore `::`'s,
precedence is too tight—it binds more tightly than the comparison operators.
One solution might be to put `::` and `??` at their current high precedence,
but also have `:` and `?` with the same semantics at a precedence level just
above assignment...
--
Brent Royal-Gordon
Architechies
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