--- >>> let (Just d1) = parse_date "1/1/1970"
--- >>> date_suffix d1
--- "st"
---
--- >>> let (Just d2) = parse_date "1/2/1970"
--- >>> date_suffix d2
--- "nd"
---
--- >>> let (Just d3) = parse_date "1/3/1970"
--- >>> date_suffix d3
--- "rd"
---
--- >>> let (Just d4) = parse_date "1/4/1970"
--- >>> date_suffix d4
--- "th"
+-- >>> let dates = [ "1/" ++ (d : "/1970") | d <- ['1'..'9'] ]
+-- >>> let suffixes = map (date_suffix . fromJust . parse_date) dates
+-- >>> suffixes
+-- ["st","nd","rd","th","th","th","th","th","th"]