From 57c56564d15cd5c83a4f1d1bab5490e6b75e8656 Mon Sep 17 00:00:00 2001
From: Gregor Kleen <gkleen@yggdrasil.li>
Date: Mon, 18 Jan 2016 12:09:36 +0000
Subject: Moved Printout.BBCode to own module

---
 .../src/Thermoprint/Printout/BBCode/Attribute.hs   | 39 ++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 tp-bbcode/src/Thermoprint/Printout/BBCode/Attribute.hs

(limited to 'tp-bbcode/src/Thermoprint/Printout/BBCode')

diff --git a/tp-bbcode/src/Thermoprint/Printout/BBCode/Attribute.hs b/tp-bbcode/src/Thermoprint/Printout/BBCode/Attribute.hs
new file mode 100644
index 0000000..538cca2
--- /dev/null
+++ b/tp-bbcode/src/Thermoprint/Printout/BBCode/Attribute.hs
@@ -0,0 +1,39 @@
+{-# LANGUAGE DefaultSignatures #-}
+
+-- | Parsing attributes
+module Thermoprint.Printout.BBCode.Attribute
+       ( Attribute(..)
+       , lookupAttr
+       ) where
+
+import Data.Text (Text)
+import qualified Data.Text as T (unpack, empty)
+
+import Data.Map (Map)
+import qualified Data.Map as Map (lookup)
+
+import Data.CaseInsensitive (CI)
+import qualified Data.CaseInsensitive as CI
+  
+import Text.Read (readMaybe)
+import Data.Maybe (fromMaybe)
+
+import Control.Applicative (Alternative(..))
+
+-- | We build our own version of 'Read' so we can override the presentation used
+--
+-- We provide a default implementation for 'Read a => Attribute a'
+class Attribute a where
+  attrRead :: Text -> Maybe a
+  default attrRead :: Read a => Text -> Maybe a
+  attrRead = readMaybe . T.unpack
+
+instance Attribute Integer
+
+lookupAttr :: Attribute a => CI Text -> Bool -> a -> Map (CI Text) Text -> a
+-- ^ Extract an attribute by name -- the 'Bool' attribute specifies whether we additionally accept the empty string as key
+lookupAttr t emptyOk def attrs = fromMaybe def $ (emptyOk' $ Map.lookup t attrs) >>= attrRead
+  where
+    emptyOk'
+      | emptyOk   = (<|> Map.lookup (CI.mk T.empty) attrs)
+      | otherwise = id
-- 
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