This is a simple one, I hope. 
How do I check, in the following example, if a constant is already defined?

```
#this works
var = var||1
puts var
var = var||2
puts var

#this doesn't
CONST = CONST||1
puts CONST
CONST = CONST||2
puts CONST

=> 1
   1
   uninitialized constant CONST (NameError)

```