Use files rather than memory to store cached values.

server/Cache.hs

@@ -0,0 +1,30 @@
+module Cache (lookupCache, insertCache) where
+
+import Control.Concurrent
+import Control.Exception
+import qualified Data.IntMap as M
+import System.Directory
+import System.FilePath
+import qualified Data.Text as T
+import qualified Data.Text.IO as T
+import Data.Text (Text)
+import Data.Hashable
+
+valueFilePath :: Text -> IO FilePath
+valueFilePath key = do
+  tmp <- getTemporaryDirectory
+  return $ tmp </> "reanimate" ++ show (hash key) <.> "svgs"
+
+
+insertCache :: Text -> [Text] -> IO ()
+insertCache key value = do
+  cacheFile <- valueFilePath key
+  T.writeFile cacheFile (T.unlines value)
+
+lookupCache :: Text -> IO (Maybe [Text])
+lookupCache key = do
+    cacheFile <- valueFilePath key
+    do svgs <- T.lines <$> T.readFile cacheFile
+       evaluate (svgs)
+       return (Just svgs)
+     `catch` \SomeException{} -> return Nothing