Is self a valid Base64 character ?

Property definitions

base64 :: base64 $ Int :: is_base64_char
	# Is `self` a valid Base64 character ?
	fun is_base64_char: Bool do
		if self == u'+' then return true
		if self == u'/' then return true
		if self > u'Z' then
			if self < u'a' then return false
			if self <= u'z' then return true
			return false
		end
		if self >= u'A' then return true
		if self <= u'9' and self >= u'0' then return true
		return false
	end
lib/base64/base64.nit:29,2--41,4