let parse_pin (_,s) =
try
let substrings = Pcre.exec ~rex:pin_regexp s
in
match Pcre.get_substring substrings 1 with
|"release" -> Pref.Release (parse_pref_labels (Pcre.get_substring substrings 2))
|"version" -> Pref.Version (Pcre.get_substring substrings 2)
|"origin" -> Pref.Origin (Pcre.get_substring substrings 2)
|s -> fatal "Unknown pin type %s" s
with Not_found -> fatal "Unknown pin format %s" s