# Returns true if the char is an alpha digit
	#
	# ~~~
	# assert 'a'.is_alpha
	# assert 'Z'.is_alpha
	# assert not '0'.is_alpha
	# assert not '?'.is_alpha
	# ~~~
	#
	# FIXME: Works on ASCII-range only
	fun is_alpha: Bool
	do
		return (self >= 'a' and self <= 'z') or (self >= 'A' and self <= 'Z')
	end