diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Changelog for Shakebook
 
+## (v0.9.1.0)
+
+* Add [ixset-typed-conversions] for producing `Zipper`s and `HashMap`s.
+
 ## (v0.9.0.0)
 
 * Upgrade shake-plus to v0.2.0.0.
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,30 +1,19 @@
-Copyright Author name here (c) 2020
-
-All rights reserved.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-    * Redistributions of source code must retain the above copyright
-      notice, this list of conditions and the following disclaimer.
+Copyright (c) 2020 Daniel Firth
 
-    * Redistributions in binary form must reproduce the above
-      copyright notice, this list of conditions and the following
-      disclaimer in the documentation and/or other materials provided
-      with the distribution.
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
 
-    * Neither the name of Author name here nor the names of other
-      contributors may be used to endorse or promote products derived
-      from this software without specific prior written permission.
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
 
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/shakebook.cabal b/shakebook.cabal
--- a/shakebook.cabal
+++ b/shakebook.cabal
@@ -3,11 +3,9 @@
 -- This file has been generated from package.yaml by hpack version 0.34.2.
 --
 -- see: https://github.com/sol/hpack
---
--- hash: d51cba8eefdc72fd7c27853b87aa1102c72c70eca86771288580e17b499255cf
 
 name:           shakebook
-version:        0.9.0.0
+version:        0.9.1.0
 synopsis:       Shake-based technical documentation generator; HTML & PDF
 description:    Shakebook is a documentation generator aimed at covering all the bases for mathematical, technical and scientific diagrams and typesetting. Shakebook provides combinators for taking markdown files and combining them into documents, but allowing the user to control how. Shakebook provides general combinators for templating single pages, cofree comonads for representing tables of contents, and zipper comonads for representing pagers.
 category:       Web
@@ -47,8 +45,10 @@
     , doctemplates
     , feed
     , free
+    , hashable-time
     , http-conduit
     , ixset-typed >=0.5
+    , ixset-typed-conversions
     , lens
     , lens-aeson
     , mustache
@@ -84,8 +84,10 @@
     , doctemplates
     , feed
     , free
+    , hashable-time
     , http-conduit
     , ixset-typed >=0.5
+    , ixset-typed-conversions
     , lens
     , lens-aeson
     , mustache
diff --git a/src/Shakebook/Conventions.hs b/src/Shakebook/Conventions.hs
--- a/src/Shakebook/Conventions.hs
+++ b/src/Shakebook/Conventions.hs
@@ -61,6 +61,8 @@
 , SrcFile(..)
 , postIndex
 , postZipper
+, fromYearMonthPair
+, toYearMonthPair
 ) where
 
 import           Control.Comonad.Cofree
@@ -70,7 +72,9 @@
 import           Data.Aeson                   as A
 import           Data.Aeson.Lens
 import           Data.Aeson.With
+import           Data.Hashable.Time
 import           Data.IxSet.Typed             as Ix
+import           Data.IxSet.Typed.Conversions as Ix
 import           Data.Text.Time
 import           Development.Shake.Plus
 import           RIO                          hiding (view)
@@ -219,30 +223,36 @@
 
 -- | Indexable Post Type
 newtype Post = Post { unPost :: Value }
-  deriving (Show, Eq, Ord, Data, Typeable, ToJSON)
+  deriving (Show, Eq, Ord, Data, Typeable, Hashable, ToJSON)
 
 -- | Tag indices for a `Post` for use with `IxSet`.
 newtype Tag = Tag Text
-  deriving (Show, Eq, Ord, Data, Typeable)
+  deriving (Show, Eq, Ord, Data, Typeable, Hashable)
 
 -- | Posted index for a `Post` for use with `IxSet`.
 newtype Posted = Posted UTCTime
-  deriving (Show, Eq, Ord, Data, Typeable)
+  deriving (Show, Eq, Ord, Data, Typeable, Hashable)
 
 -- | YearMonth (yyyy, mm) index for a `Post` for use with `IxSet`.
 newtype YearMonth = YearMonth (Integer, Int)
-  deriving (Show, Eq, Ord, Data, Typeable)
+  deriving (Show, Eq, Ord, Data, Typeable, Hashable)
 
 -- | SrcFile index for a `Post` for use with `IxSet`.
 newtype SrcFile = SrcFile Text
-  deriving (Show, Eq, Ord, Data, Typeable)
+  deriving (Show, Eq, Ord, Data, Typeable, Hashable)
 
 instance Indexable '[Tag, Posted, YearMonth, SrcFile] Post where
   indices = ixList (ixFun (fmap Tag . viewTags))
                    (ixFun (pure . Posted . viewPostTime))
-                   (ixFun (pure . YearMonth . (\(a,b,_) -> (a,b)) . toGregorian . utctDay . viewPostTime))
+                   (ixFun (pure . YearMonth . toYearMonthPair . viewPostTime))
                    (ixFun (pure . SrcFile . viewSrcPath))
 
+toYearMonthPair :: UTCTime -> (Integer, Int)
+toYearMonthPair = (\(a, b, _) -> (a, b)) . toGregorian . utctDay
+
+fromYearMonthPair :: (Integer, Int) -> UTCTime
+fromYearMonthPair (y,m) = UTCTime (fromGregorian y m 1) 0
+
 -- | Take a Value loading function and a filepattern and return an indexable set of Posts.
 postIndex :: MonadAction m
           => (Within Rel (Path Rel File) -> m Value)
@@ -254,7 +264,7 @@
 
 -- | Create a `Zipper [] Post` from an `IxSet xs Post` by ordering by `Posted`.
 postZipper :: (MonadThrow m, Ix.IsIndexOf Posted xs) => Ix.IxSet xs Post -> m (Zipper [] Post)
-postZipper = zipper' . Ix.toDescList (Proxy :: Proxy Posted)
+postZipper = Ix.toZipperDesc (Proxy :: Proxy Posted)
 
 -- | Create a blog navbar object for a posts section, with layers "toc1", "toc2", and "toc3".
 genBlogNavbarData :: IsIndexOf YearMonth ixs => Text -- ^ "Top level title, e.g "Blog"
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -2,7 +2,9 @@
 
 import           Data.Aeson.With
 import qualified Data.IxSet.Typed as Ix
+import qualified Data.IxSet.Typed.Conversions as Ix
 import           Data.List.Split
+import           Data.Text.Time
 import           Path.Extensions
 import           RIO
 import qualified RIO.HashMap       as HM
@@ -10,7 +12,6 @@
 import           RIO.List.Partial
 import           RIO.Partial
 import qualified RIO.Text          as T
-import           RIO.Time
 import           Shakebook
 import           Test.Tasty
 import           Test.Tasty.Golden
@@ -55,6 +56,19 @@
 myDocNav :: Cofree [] Value -> Value
 myDocNav = genTocNavbarData
 
+myIndex :: MonadThrow m => [Post] -> m (Zipper [] Value)
+myIndex = genIndexPageData "Posts" ("/posts/pages/" <>) postsPerPage
+
+myTagIndex :: MonadThrow m => Tag -> [Post] -> m (Zipper [] Value)
+myTagIndex (Tag t) = genIndexPageData ("Posts tagged " <> t) (("/posts/tags/" <> t <> "/pages/") <>) postsPerPage
+
+myMonthIndex :: MonadThrow m => YearMonth -> [Post] -> m (Zipper [] Value)
+myMonthIndex (YearMonth (y, m)) =
+  let t' = fromYearMonthPair (y, m)
+  in genIndexPageData (("Posts from " <>) . defaultPrettyMonthFormat $ t')
+                      (("/posts/months/"  <> defaultMonthUrlFormat t' <> "/pages/") <>)
+                      postsPerPage
+
 rules :: HasLogFunc r => ShakePlus r ()
 rules = do
 
@@ -66,31 +80,17 @@
 
   postsZ    <- newCache $ postsIx >=> postZipper
 
-  blogIndex <- newCache $ postsIx >=> genIndexPageData "Posts" ("/posts/pages/" <>) postsPerPage . Ix.toList
-
-  blogTagIndex <- newCache $ \fp -> do
-    xs <- postsIx fp
-    k <- forM (Ix.groupDescBy xs) $ \(Tag t, ys) -> do
-      z <- genIndexPageData ("Posts tagged " <> t) (("/posts/tags/" <> t <> "/pages/") <>) postsPerPage ys
-      return (t, z)
-    return $ HM.fromList k
+  blogIndex <- newCache $ postsIx >=> myIndex . Ix.toList
 
-  blogMonthIndex <- newCache $ \fp -> do
-    xs <- postsIx fp
-    k <- forM (Ix.groupDescBy xs) $ \(YearMonth (y,m), ys) -> do
-      let t' = UTCTime (fromGregorian y m 1) 0
-      z <- genIndexPageData (("Posts from " <>) . defaultPrettyMonthFormat $ t')
-                            (("/posts/months/"  <> defaultMonthUrlFormat t' <> "/pages/") <>)
-                            postsPerPage
-                            ys
-      return (defaultMonthUrlFormat t', z)
-    return $ HM.fromList k
+  blogTagIndex <- newCache $ postsIx >=> flip Ix.toHashMapByM myTagIndex
 
-  let myPosts = ["posts/*.md"] `within` sourceFolder
+  blogMonthIndex <- newCache $ postsIx >=> flip Ix.toHashMapByM myMonthIndex
 
-      o' = (`within` outputFolder)
+  let o' = (`within` outputFolder)
       s' = (`within` sourceFolder)
 
+      myPosts = s' ["posts/*.md"]
+
       myBuildPage tmpl v out = do
         rs <- postsZ myPosts
         let v' = withHighlighting pygments
@@ -142,11 +142,11 @@
 
   o' "posts/tags/*/pages/*/index.html" %^> \out -> do
      let zs = splitOn "/" . toFilePath . extract $ out
-     let t = T.pack $ zs !! 2
+     let t = Tag $ T.pack $ zs !! 2
      let n = read   $ zs !! 4
      xs <- blogTagIndex myPosts
      case HM.lookup t xs of
-       Nothing -> logError $ "Attempting to lookup non-existant tag " <> display t
+       Nothing -> logError $ "Attempting to lookup non-existant tag " <> displayShow t
        Just x  -> myBuildPostListPage (seek (n - 1) x) out
 
   o' "posts/months/*/index.html" %^> \out -> do
@@ -156,7 +156,7 @@
 
   o' "posts/months/*/pages/*/index.html" %^> \out -> do
      let zs = splitOn "/" . toFilePath . extract $ out
-     let t = T.pack $ zs !! 2
+     let t = YearMonth $ toYearMonthPair $ parseISODateTime $ T.pack $ zs !! 2
      let n = read   $ zs !! 4
      xs <- blogMonthIndex myPosts
      case HM.lookup t xs of
@@ -185,7 +185,7 @@
 
   phony "by-tag-index" $ do
      ps <- blogTagIndex myPosts
-     void $ flip HM.traverseWithKey ps $ \t z -> do
+     void $ flip HM.traverseWithKey ps $ \(Tag t) z -> do
        u  <- parseRelDir $ T.unpack t
        fs <- defaultPagePaths [1..size z]
        let tagFolder = outputFolder </> $(mkRelDir "posts/tags") </> u
@@ -193,8 +193,8 @@
 
   phony "by-month-index" $ do
      ps <- blogMonthIndex myPosts
-     void $ flip HM.traverseWithKey ps $ \t z -> do
-       u  <- parseRelDir $ T.unpack t
+     void $ flip HM.traverseWithKey ps $ \(YearMonth t) z -> do
+       u  <- parseRelDir $ T.unpack $ defaultMonthUrlFormat $ fromYearMonthPair $ t
        fs <- defaultPagePaths [1..size z]
        let monthFolder = outputFolder </> $(mkRelDir "posts/months") </> u
        needIn monthFolder ($(mkRelFile "index.html") : fs)