Added a simple 'showMarketPrice' function to show market price directives in a journal-compatible way (#505)

* added showMarketPrice and Hledger.Data.MarketPrice module

* showMarketPrice implemented using showDate

* attempted to add tests to Hledger.Data.MarketPrice

* moved MarketPrice test to Hledger.Read.JournalReader; fixed documentation on MarketPrice; added MarketPrice module to package.yaml

hledger-lib/Hledger/Data.hs

@@ -15,6 +15,7 @@ module Hledger.Data (
                module Hledger.Data.Dates,
                module Hledger.Data.Journal,
                module Hledger.Data.Ledger,
+               module Hledger.Data.MarketPrice,
                module Hledger.Data.Period,
                module Hledger.Data.Posting,
                module Hledger.Data.RawOptions,
@@ -34,6 +35,7 @@ import Hledger.Data.Commodity
 import Hledger.Data.Dates
 import Hledger.Data.Journal
 import Hledger.Data.Ledger
+import Hledger.Data.MarketPrice
 import Hledger.Data.Period
 import Hledger.Data.Posting
 import Hledger.Data.RawOptions
@@ -50,6 +52,7 @@ tests_Hledger_Data = TestList
     ,tests_Hledger_Data_Amount
     ,tests_Hledger_Data_Commodity
     ,tests_Hledger_Data_Journal
+    ,tests_Hledger_Data_MarketPrice
     ,tests_Hledger_Data_Ledger
     ,tests_Hledger_Data_Posting
     -- ,tests_Hledger_Data_RawOptions

hledger-lib/Hledger/Data/MarketPrice.hs

@@ -0,0 +1,32 @@
+{-|
+
+A 'MarketPrice' represents a historical exchange rate between two
+commodities. (Ledger calls them historical prices.) For example, prices
+published by a stock exchange or the foreign exchange market.  Some
+commands (balance, currently) can use this information to show the market
+value of things at a given date.
+
+-}
+
+{-# LANGUAGE OverloadedStrings, LambdaCase #-}
+
+module Hledger.Data.MarketPrice
+where
+import qualified Data.Text as T
+import Test.HUnit
+
+import Hledger.Data.Amount
+import Hledger.Data.Dates
+import Hledger.Data.Types
+
+-- | Get the string representation of an market price, based on its
+-- commodity's display settings.
+showMarketPrice :: MarketPrice -> String
+showMarketPrice mp = unwords
+    [ "P"
+    , showDate (mpdate mp)
+    , T.unpack (mpcommodity mp)
+    , (showAmount . setAmountPrecision maxprecision) (mpamount mp)
+    ]
+
+tests_Hledger_Data_MarketPrice = TestList []

hledger-lib/Hledger/Read/JournalReader.hs

@@ -624,6 +624,12 @@ test_postingp = do
 
 tests_Hledger_Read_JournalReader = TestList $ concat [
     -- test_numberp
+    [
+    "showParsedMarketPrice" ~: do
+      let mp = parseWithState mempty marketpricedirectivep "P 2017/01/30 BTC $922.83\n"
+          mpString = (fmap . fmap) showMarketPrice mp
+      mpString `is` (Just (Right "P 2017/01/30 BTC $922.83"))
+    ]
  ]
 
 {- old hunit tests

hledger-lib/hledger-lib.cabal

@@ -110,6 +110,7 @@ library
       Hledger.Data.Dates
       Hledger.Data.Journal
       Hledger.Data.Ledger
+      Hledger.Data.MarketPrice
       Hledger.Data.Period
       Hledger.Data.StringFormat
       Hledger.Data.Posting

hledger-lib/package.yaml

@@ -91,6 +91,7 @@ library:
   - Hledger.Data.Dates
   - Hledger.Data.Journal
   - Hledger.Data.Ledger
+  - Hledger.Data.MarketPrice
   - Hledger.Data.Period
   - Hledger.Data.StringFormat
   - Hledger.Data.Posting