function pmf( x, a, b ) {
	if (
		isnan( x ) ||
		isnan( a ) ||
		isnan( b ) ||
		!isInteger( a ) ||
		!isInteger( b ) ||
		a > b
	) {
		return NaN;
	}
	if ( x < a || x > b || !isInteger( x ) ) {
		return 0.0;
	}
	return 1.0 / ( b - a + 1.0 );
}
Evaluates the probability mass function (PMF) for a discrete uniform distribution with minimum support `a` and maximum support `b` at a value `x`.

@param {number} x - input value
@param {integer} a - minimum support
@param {integer} b - maximum support
@returns {number} evaluated PMF

@example
var y = pmf( 2.0, 0, 4 );
// returns ~0.2

@example
var y = pmf( 5.0, 0, 4 );
// returns 0.0

@example
var y = pmf( 2, 0, 8 );
// returns ~0.111

@example
var y = pmf( NaN, 0, 1 );
// returns NaN

@example
var y = pmf( 0.0, NaN, 1 );
// returns NaN

@example
var y = pmf( 0.0, 0, NaN );
// returns NaN

@example
var y = pmf( 2.0, 3, 1 );
// returns NaN