Question

I’m looking for a succinct expression for evaluating whether or not all the items in a list are either Longs or may be converted to Longs. I’m looking for a compact expression, but I prefer readability over mere code golf.

Examples:

assert expr([1,2,'3'])
assert expr([1,'fish',3]) == false
assert expr([null]) == false
assert expr([' ', 17]) == false

Answer 1

For readability, I would do something like:

def canBeLongs(things) {
    things.every { 
        try { Long.valueOf(it); true } 
        catch (e) { false }
    }
}

assert canBeLongs([1,2,'3'])
assert !canBeLongs([1,'fish',3])
assert !canBeLongs([null])
assert !canBeLongs([' ', 17])

Just for the lulz, this other solution is horrible, but it’s very succinct and covers all the test cases:

def f(l) { l.join() ==~ /[0-9]*/ }

assert f([1,2,'3'])
assert !f([1,'fish',3])
assert !f([null])
assert !f([' ', 17])