= Solution
Validate the parameter, and include exactly the outcomes of positive mass:
``
final class Flip(p: Double) extends FiniteDist[Boolean] {
require(p >= 0.0 && p <= 1.0)
def getDom: List[Boolean] =
if (p == 0.0) List(false)
else if (p == 1.0) List(true)
else List(false, true)
def getProb(x: Boolean): Double = if (x) p else 1.0 - p
}
``
The range test also rejects `NaN`, since its ordered comparisons are false. At the endpoints one outcome has zero mass and must be omitted from the support; listing both unconditionally would violate the supplied interface contract. For an interior parameter the two masses are positive and sum to one.
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