src/TSN/Location.hs

   1 {-# LANGUAGE FlexibleInstances #-}
   2 {-# LANGUAGE GADTs #-}
   3 {-# LANGUAGE QuasiQuotes #-}
   4 {-# LANGUAGE TemplateHaskell #-}
   5 {-# LANGUAGE TypeFamilies #-}
   6
   7 -- | (At least) two different XML types have a notion of locations:
   8 --   "TSN.XML.News" and "TSN.XML.Scores". And in fact those two types
   9 --   agree on the city, state, and country -- at least for the
  10 --   database representation.
  11 --
  12 --   This module contains a data type for the common database
  13 --   representation.
  14 --
  15 module TSN.Location (
  16   Location(..),
  17   pickle_location,
  18   -- * WARNING: these are private but exported to silence warnings
  19   LocationConstructor(..) )
  20 where
  21
  22 -- System imports
  23 import Data.Tuple.Curry ( uncurryN )
  24 import Database.Groundhog () -- Required for some String instance
  25 import Database.Groundhog.TH (
  26   defaultCodegenConfig,
  27   groundhog,
  28   mkPersist )
  29 import Text.XML.HXT.Core (
  30   PU,
  31   xpElem,
  32   xpOption,
  33   xpText,
  34   xpTriple,
  35   xpWrap )
  36
  37
  38 -- | Database representation of a location.
  39 --
  40 --   The country has always been present in the XML that we've
  41 --   seen. The city/state however have been observed missing in some
  42 --   cases. The Scores are better about always having a city/state,
  43 --   but in the interest of consolidation, we've made them optional so
  44 --   that they can be mushed together into this one type.
  45 --
  46 data Location =
  47   Location {
  48     city :: Maybe String,
  49     state :: Maybe String,
  50     country :: String }
  51   deriving (Eq, Show)
  52
  53
  54 -- Generate the Groundhog code for 'Location'.
  55 mkPersist defaultCodegenConfig [groundhog|
  56 - entity: Location
  57   dbName: locations
  58   constructors:
  59     - name: Location
  60       uniques:
  61         - name: unique_location
  62           type: constraint
  63           fields: [city, state, country]
  64 |]
  65
  66
  67
  68 -- | We also provide an (un)pickler for one common XML representation,
  69 --   used at least in "TSN.XML.News" and "TSN.XML.Location".
  70 --
  71 pickle_location :: PU Location
  72 pickle_location =
  73   xpElem "location" $
  74     xpWrap (from_tuple, to_tuple) $
  75     xpTriple (xpOption (xpElem "city" xpText))
  76              (xpOption (xpElem "state" xpText))
  77              (xpElem "country" xpText)
  78   where
  79     from_tuple = uncurryN Location
  80     to_tuple l = (city l, state l, country l)