--- split a string at the last occurence of 'c', returning the two
--- parts of the string with the 'c' removed. If the string contains
--- no 'c's, the entire string is returned in the second component.
-split_longest_prefix :: String -> Char -> (String,String)
-split_longest_prefix s c
+-- split a string at the last character where 'pred' is True,
+-- returning a pair of strings. The first component holds the string
+-- up (but not including) the last character for which 'pred' returned
+-- True, the second whatever comes after (but also not including the
+-- last character).
+--
+-- If 'pred' returns False for all characters in the string, the original
+-- string is returned in the second component (and the first one is just
+-- empty).
+split_longest_prefix :: String -> (Char -> Bool) -> (String,String)
+split_longest_prefix s pred