From a5647e17247232f8cb05379ce046142248810f31 Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbaren@mit.edu>
Date: Wed, 11 Feb 2015 20:51:34 -0500
Subject: Fragment: Give up and use pattern matching
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I’m normally opposed to pattern matching in high-quality apps, but this
is so small that I’m unconvinced it’ll be a problem.  I can always
switch to explicit accessors if things get too coupled.
---
 lyt.cabal       |  1 +
 src/Fragment.hs | 17 +----------------
 src/Main.hs     |  1 +
 src/Tangle.hs   | 38 +++++++++++++++++++++++---------------
 4 files changed, 26 insertions(+), 31 deletions(-)

diff --git a/lyt.cabal b/lyt.cabal
index 5f55390..471b44d 100644
--- a/lyt.cabal
+++ b/lyt.cabal
@@ -39,6 +39,7 @@ executable lyt
   main-is:             Main.hs
   other-modules:       Fragment
                      , Tangle
+                     , Weave
   build-depends:       base >=4.6 && <4.7
                      , containers >=0.5 && <0.6
                      , parsec >=3.1.3 && <3.2
diff --git a/src/Fragment.hs b/src/Fragment.hs
index 14172da..6850662 100644
--- a/src/Fragment.hs
+++ b/src/Fragment.hs
@@ -12,11 +12,8 @@ PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 You should have received a copy of the GNU General Public License along with
 this program.  If not, see <http://www.gnu.org/licenses/>. -}
 
-{-# LANGUAGE RecordWildCards #-}
-module Fragment ( Fragment
+module Fragment ( Fragment(..)
                 , CodeOrReference(..)
-                , isBlockCode
-                , blockName, blockContents
                 , parseStdin
                 , parseFile) where
 
@@ -34,18 +31,6 @@ data Fragment = Documentation String
               | BlockCode String [CodeOrReference]
               deriving (Eq, Show, Data, Typeable, Generic)
 
-isBlockCode :: Fragment -> Bool
-isBlockCode (Documentation {..}) = False
-isBlockCode (BlockCode {..}) = True
-
-blockName :: Fragment -> String
-blockName (Documentation {..}) = error "Documentation fragments are unnamed"
-blockName (BlockCode name _) = name
-
-blockContents :: Fragment -> [CodeOrReference]
-blockContents (Documentation {..}) = error "Documentation fragments have no code"
-blockContents (BlockCode _ body) = body
-
 data CodeOrReference = Code String
                      | Reference String
                      deriving (Eq, Show, Data, Typeable, Generic)
diff --git a/src/Main.hs b/src/Main.hs
index 74ea1d2..bf81ae2 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -19,6 +19,7 @@ import System.Exit (exitFailure)
 
 import Fragment (parseFile, parseStdin)
 import Tangle (tangle)
+import Weave (weave)
 
 main :: IO ()
 main = do
diff --git a/src/Tangle.hs b/src/Tangle.hs
index 049c497..edfd6ed 100644
--- a/src/Tangle.hs
+++ b/src/Tangle.hs
@@ -12,6 +12,7 @@ PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 You should have received a copy of the GNU General Public License along with
 this program.  If not, see <http://www.gnu.org/licenses/>. -}
 
+{-# LANGUAGE RecordWildCards #-}
 module Tangle (tangle) where
 
 import Control.Exception (assert)
@@ -19,8 +20,7 @@ import Control.Monad (liftM)
 import Data.Map.Strict (Map)
 import qualified Data.Map.Strict as Map
 
-import Fragment (Fragment, isBlockCode, blockName, blockContents,
-                 CodeOrReference(Code, Reference))
+import Fragment (Fragment(..), CodeOrReference(..))
 
 type FragmentGraph = Map String [CodeOrReference]
 
@@ -28,24 +28,32 @@ tangle :: [Fragment] -> Either String String
 tangle fragments =
   case filter isBlockCode fragments of
     [] -> Right ""
-    codeBlocks@(root:_) ->
-      expandBlock (fragmentGraph codeBlocks) (blockName root)
+    blockCodeFragments@((BlockCode rootName _):_) ->
+      expandBlockCodeFragment (fragmentGraph blockCodeFragments) rootName
+    (Documentation {..}):_ -> error "isBlockCode did not work correctly"
 
 fragmentGraph :: [Fragment] -> FragmentGraph
-fragmentGraph frags =
-  Map.fromListWith (++) $
-    map (\block -> blockToPair $ assert (isBlockCode block) block) frags
-  where blockToPair frag = (blockName frag, blockContents frag)
-
-expandBlock :: FragmentGraph -> String -> Either String String
-expandBlock fragments name =
+fragmentGraph =
+  Map.fromListWith (++) .
+    map (\block -> blockToPair $ assert (isBlockCode block) block)
+  where blockToPair (BlockCode name body) = (name, body)
+        blockToPair (Documentation {..}) =
+          error "Documentation fragments cannot be converted to pairs"
+
+expandBlockCodeFragment :: FragmentGraph -> String -> Either String String
+expandBlockCodeFragment fragments name =
   case Map.lookup name fragments of
     Nothing -> Left $ "Desired node " ++ name ++ " not in fragment graph"
-    Just block -> concatMapM (expandBlockBody1 fragments) block
+    Just block -> concatMapM (expandBlockCodeBody fragments) block
+
+expandBlockCodeBody :: FragmentGraph -> CodeOrReference -> Either String String
+expandBlockCodeBody _ (Code body) = Right body
+expandBlockCodeBody fragments (Reference name) =
+  expandBlockCodeFragment fragments name
 
-expandBlockBody1 :: FragmentGraph -> CodeOrReference -> Either String String
-expandBlockBody1 _ (Code body) = Right body
-expandBlockBody1 fragments (Reference name) = expandBlock fragments name
+isBlockCode :: Fragment -> Bool
+isBlockCode (Documentation {..}) = False
+isBlockCode (BlockCode {..}) = True
 
 concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
 concatMapM f lists = liftM concat $ mapM f lists
-- 
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