docbook2txt: clean up some code

- Introduce pattern synonym `TextLeaf` for `TagLeaf (TagText)`
- Convert `replaceTagColor` to use "case-of" pattern matching

internals/docbook2txt/docbook2txt.hs

@@ -9,6 +9,8 @@
 --   consumed by pandoc anyway. So instead, I am just planning on keeping
 --   my own module parsing raw xml tags (for now).
 
+{-# LANGUAGE PatternSynonyms #-}
+
 import Data.List (find, intersperse)
 import Data.List.Split (splitOn)
 import qualified System.Console.ANSI as AN
@@ -67,85 +69,83 @@ wrapTxt delimiter string = concat [delimiter, string, delimiter]
 bold :: AN.SGR
 bold = AN.SetConsoleIntensity AN.BoldIntensity
 
+pattern TextLeaf a = TS.TagLeaf (TS.TagText a)
+
 -- Replace tags with their PCS string equivalent.
 replaceTagColor :: TS.TagTree String -> PotentiallyColorizedString
-replaceTagColor (TS.TagLeaf (TS.TagText s)) =
+replaceTagColor tagtree = case tagtree of
+  TS.TagLeaf (TS.TagText s) ->
     PCS
       { colorized = putStr s,
         nonColorized = s
       }
-replaceTagColor (TS.TagBranch "para" _ inner) =
+  TS.TagBranch "para" _ inner ->
     PCS
       { colorized = mapM_ (colorized . replaceTagColor) inner,
         nonColorized = concatMap (nonColorized . replaceTagColor) inner
       }
-replaceTagColor (TS.TagBranch "code" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "code" _ [TextLeaf content] ->
     PCS
       { colorized = wrapSGR bold $ wrapTxt "`" content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "command" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "command" _ [TextLeaf content] ->
     PCS
       { colorized = wrapSGR bold $ wrapTxt "`" content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "filename" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "filename" _ [TextLeaf content] ->
     PCS
       { colorized = wrapColor AN.Yellow content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "emphasis" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "emphasis" _ [TextLeaf content] ->
     PCS
       { colorized = wrapSGR bold content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "literal" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "literal" _ [TextLeaf content] ->
     PCS
       { colorized = wrapColor AN.Red content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "varname" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "varname" _ [TextLeaf content] ->
     PCS
       { colorized = wrapColor AN.Red content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "link" [("xlink:href", link)] []) =
+  TS.TagBranch "link" [("xlink:href", link)] [] ->
     PCS
       { colorized = wrapColor AN.Blue link,
         nonColorized = concat ["`", link, "`"]
       }
-replaceTagColor (TS.TagBranch "link" [("xlink:href", link)] [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "link" [("xlink:href", link)] [TextLeaf content] ->
     PCS
       { colorized = wrapColor AN.Blue $ concat [content, " (", link, ")"],
         nonColorized = concat ["`", content, " (", link, ")`"]
       }
-replaceTagColor (TS.TagBranch "option" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "option" _ [TextLeaf content] ->
     PCS
       { colorized = wrapSGR bold $ wrapTxt "`" content,
         nonColorized = wrapTxt "`" content
       }
-replaceTagColor (TS.TagBranch "envar" _ [TS.TagLeaf (TS.TagText content)]) =
+  TS.TagBranch "envar" _ [TextLeaf content] ->
     PCS
       { colorized = wrapSGR bold $ concat ["`$", content, "`"],
         nonColorized = concat ["`$", content, "`"]
       }
-replaceTagColor (TS.TagBranch "quote" _ inner) =
+  TS.TagBranch "quote" _ inner ->
     PCS
       { colorized = sequence_ [putStr "\"", mapM_ (colorized . replaceTagColor) inner, putStr "\""],
         nonColorized = wrapTxt "\"" $ concatMap (nonColorized . replaceTagColor) inner
       }
-replaceTagColor (TS.TagBranch "warning" _ inner) =
+  TS.TagBranch "warning" _ inner ->
     PCS
       { colorized = sequence_ [wrapColor AN.Red "WARNING: ", mapM_ (colorized . replaceTagColor) inner],
         nonColorized = "WARNING: " ++ concatMap (nonColorized . replaceTagColor) inner
       }
-replaceTagColor (TS.TagBranch "xref" [("linkend", link)] []) =
-  PCS
-    { colorized = sequence_ $ [putStr "`"] ++ formattedLink ++ [putStr "`"],
-      nonColorized = wrapTxt "`" link
-    }
-  where
-    removeOptPrefix :: String -> String
+  TS.TagBranch "xref" [("linkend", link)] [] ->
+    let removeOptPrefix :: String -> String
         removeOptPrefix ('o' : 'p' : 't' : '-' : rest) = rest
         removeOptPrefix x = x
 
@@ -154,24 +154,23 @@ replaceTagColor (TS.TagBranch "xref" [("linkend", link)] []) =
 
         formattedLink :: [IO ()]
         formattedLink = intersperse (wrapSGR bold ".") $ map replaceName $ splitOn "." $ removeOptPrefix link
-replaceTagColor (TS.TagBranch "citerefentry" _ content) =
-  PCS
-    { colorized = wrapColor AN.Blue combinedLink,
-      nonColorized = combinedLink
+     in PCS
+          { colorized = sequence_ $ [putStr "`"] ++ formattedLink ++ [putStr "`"],
+            nonColorized = wrapTxt "`" link
           }
-  where
-    tagBranchTagMatches :: String -> TS.TagTree String -> Bool
+  TS.TagBranch "citerefentry" _ content ->
+    let tagBranchTagMatches :: String -> TS.TagTree String -> Bool
         tagBranchTagMatches x (TS.TagBranch tag _ _) = tag == x
         tagBranchTagMatches _ _ = False
 
         title :: Maybe String
         title = case find (tagBranchTagMatches "refentrytitle") content of
-      Just (TS.TagBranch _ _ [TS.TagLeaf (TS.TagText str)]) -> Just str
+          Just (TS.TagBranch _ _ [TextLeaf str]) -> Just str
           _ -> Nothing
 
         volumNum :: Maybe String
         volumNum = case find (tagBranchTagMatches "manvolnum") content of
-      Just (TS.TagBranch _ _ [TS.TagLeaf (TS.TagText str)]) -> Just str
+          Just (TS.TagBranch _ _ [TextLeaf str]) -> Just str
           _ -> Nothing
 
         combinedLink :: String
@@ -179,7 +178,11 @@ replaceTagColor (TS.TagBranch "citerefentry" _ content) =
           (Just t, Just vn) -> concat [t, "(", vn, ")"]
           (Just t, Nothing) -> t
           _ -> "???"
-replaceTagColor unknown =
+     in PCS
+          { colorized = wrapColor AN.Blue combinedLink,
+            nonColorized = combinedLink
+          }
+  unknown ->
     PCS
       { colorized = wrapColor AN.Red $ TS.renderTree [unknown],
         nonColorized = TS.renderTree [unknown]