You probably want some parentheses. The concatenation operator (period) binds more tightly than the list operator (comma), so your code as it stands is doing the second join, then the concatenation (which evaluates the slice in scalar context), then the first join (thus, no hyphens, because the concatenation produces only one value for join to join). Put parentheses around the first join to make it evaluate before the concatenation, and Bjorn Stronginthearm is your uncle.