Defining a static array with values in a range

[tcak via Digitalmars-d-learn]

I want to define alphanumeric characters in an easy way. 
Something like that:

char[] arr = ['a'..'z', 'A'..'Z', '0'..'9'];
Though above example doesn't work. Is there any easy way to do 
this?

I am trying to do something like EBNF definitions. So, I do not 
want to use loops, or define every single thing one by one by 
hand.