diff --git a/Control/Monad/Trans/Writer/JSONable.hs b/Control/Monad/Trans/Writer/JSONable.hs
--- a/Control/Monad/Trans/Writer/JSONable.hs
+++ b/Control/Monad/Trans/Writer/JSONable.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
@@ -17,7 +17,7 @@
 module Control.Monad.Trans.Writer.JSONable where
 
 import Data.Aeson
-import Data.Flat
+import Flat
 import GHC.Generics
 import Data.Semigroup
 
diff --git a/Data/Traversable/Redundancy.hs b/Data/Traversable/Redundancy.hs
--- a/Data/Traversable/Redundancy.hs
+++ b/Data/Traversable/Redundancy.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
diff --git a/Presentation/Yeamer.hs b/Presentation/Yeamer.hs
--- a/Presentation/Yeamer.hs
+++ b/Presentation/Yeamer.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
@@ -20,11 +20,16 @@
 {-# LANGUAGE OverloadedStrings      #-}
 {-# LANGUAGE GADTs                  #-}
 {-# LANGUAGE ScopedTypeVariables    #-}
+{-# LANGUAGE DefaultSignatures      #-}
+{-# LANGUAGE EmptyCase              #-}
 {-# LANGUAGE UnicodeSyntax          #-}
 {-# LANGUAGE TupleSections          #-}
+{-# LANGUAGE TypeOperators          #-}
 {-# LANGUAGE ConstraintKinds        #-}
 {-# LANGUAGE ViewPatterns           #-}
 {-# LANGUAGE Rank2Types             #-}
+{-# LANGUAGE TypeApplications       #-}
+{-# LANGUAGE AllowAmbiguousTypes    #-}
 
 module Presentation.Yeamer ( Presentation
                            -- * Running a presentation
@@ -39,10 +44,17 @@
                            , useFile, useFileSupplier
                            -- ** Code / plaintext
                            , verbatim, plaintext, verbatimWithin
+                           -- ** Haskell values
+                           , InteractiveShow(..)
+                           -- ** Interactive parameters
+                           , inputBox, feedback_
                            -- * Structure / composition
                            , addHeading, (======), discardResult
                            , module Data.Monoid
                            , module Data.Semigroup.Numbered
+                           , (→│←)
+                           , (→│)
+                           , (→│→)
                            -- * CSS
                            , divClass, divClasses, spanClass, (#%), styling, Css
                            -- * Server configuration
@@ -63,7 +75,7 @@
 import Data.ByteString (ByteString)
 import qualified Data.ByteString.Lazy as BSL
 import qualified Data.ByteString.Char8 as BC8
-import Data.Flat (Flat, flat, unflat)
+import Flat (Flat, flat, unflat)
 import qualified Data.Aeson as JSON
 import qualified Text.Blaze.Html5 as HTM
 import qualified Text.Blaze.Html5.Attributes as HTM
@@ -75,14 +87,17 @@
 import qualified Data.Vector as Arr
 import Presentation.Yeamer.Internal.Grid
 
-import Text.Cassius (Css)
-import Text.Julius (rawJS)
+import Text.Cassius (cassius, Css)
+import Text.Julius (rawJS, Javascript)
 
 import Yesod.Static (Static, static, base64md5)
 import Yesod.EmbeddedStatic
 import qualified Language.Javascript.JQuery as JQuery
 import Language.Haskell.TH.Syntax ( Exp(LitE, AppE, VarE, ConE)
                                   , Lit(StringL), Name, runIO )
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import GHC.Stack (HasCallStack)
+import Data.Int (Int64, Int32, Int16)
 import Language.Haskell.TH.Quote
 
 import qualified CAS.Dumb.Symbols as TMM
@@ -92,6 +107,7 @@
 import qualified Text.LaTeX as LaTeX
 import qualified Text.TeXMath as MathML
 import qualified Text.XML.Light as XML
+import Text.Printf
 
 import Data.List (intercalate)
 import Data.Foldable (fold)
@@ -102,6 +118,7 @@
 import Control.Monad.Trans.Reader
 import Data.These
 import Data.These.Lens
+import Data.Either (partitionEithers)
 import qualified Data.Semigroup as SG
 import Data.Semigroup.Numbered
 import Data.Monoid
@@ -113,6 +130,7 @@
 
 import Data.Function ((&))
 import Data.Tuple (swap)
+import Data.Proxy
 import Data.Default.Class
 
 import System.FilePath ( takeFileName, takeExtension, takeBaseName, dropExtension
@@ -166,14 +184,25 @@
 
 data IPresentation m r where
    StaticContent :: Html -> IPresentation m ()
+   TweakableInput :: (Sessionable x, JSON.FromJSON x)
+        => Maybe x
+         -> ( PrPath -> ( Text   -- ^ The “final leaf” of the DOM path
+                      , Maybe x -> -- ^ An already stored value
+                         ( PresProgress -> JavascriptUrl (Route PresentationServer)
+                         , Html )
+                      ))
+                          -> IPresentation m (Maybe x)
    Resultless :: IPresentation m r -> IPresentation m ()
    Styling :: [Css] -> IPresentation m r -> IPresentation m r
-   Encaps :: (Traversable t, Sessionable r, Sessionable (t ()))
-               => Container t -> t (IPresentation m r) -> IPresentation m (t r)
+   Encaps :: (Traversable t, Sessionable r, Sessionable rf, Sessionable (t ()))
+               => Container t -> (t r -> rf)
+                   -> t (IPresentation m r) -> IPresentation m rf
    Pure :: r -> IPresentation m r
    Deterministic :: (r -> s) -> IPresentation m r -> IPresentation m s
    Interactive :: Sessionable r
           => IPresentation m () -> m r -> IPresentation m r
+   Feedback :: Sessionable r
+           => (Maybe r -> IPresentation m r) -> IPresentation m r
    Dependent :: Sessionable x
                    => IPresentation m x -> (x -> IPresentation m r) -> IPresentation m r
 instance (r ~ ()) => IsString (IPresentation m r) where
@@ -196,6 +225,7 @@
 / HomeR GET
 /p/#PresProgress ExactPositionR GET
 /changeposition/#PresProgress/#PositionChange ChPosR GET
+/setvalue/#PresProgress/#PrPath/#ValueToSet SetValR GET
 /reset ResetR GET
 /static StaticR EmbeddedStatic getStatic
 /pseudostatic PStaticR Static getPseudostatic
@@ -207,18 +237,19 @@
 
 preprocPres :: IPresentation m r -> IPresentation m r
 preprocPres (StaticContent c) = StaticContent c
+preprocPres (TweakableInput defV frm) = TweakableInput defV frm
 preprocPres (Resultless p) = Resultless $ preprocPres p
 preprocPres (Styling s p) = Styling s $ preprocPres p
-preprocPres (Encaps (WithHeading h) p) = Encaps (WithHeading h) $ preprocPres<$>p
-preprocPres (Encaps ManualCSSClasses p) = Encaps ManualCSSClasses $ preprocPres<$>p
-preprocPres (Encaps (CustomEncapsulation (EncapsulableWitness w) f) p)
-                = Encaps (CustomEncapsulation (EncapsulableWitness w) f) $ preprocPres<$>p
-preprocPres (Encaps GriddedBlocks p)
+preprocPres (Encaps (WithHeading h) ff p) = Encaps (WithHeading h) ff $ preprocPres<$>p
+preprocPres (Encaps ManualCSSClasses ff p) = Encaps ManualCSSClasses ff $ preprocPres<$>p
+preprocPres (Encaps (CustomEncapsulation (EncapsulableWitness w) f) ff p)
+                = Encaps (CustomEncapsulation (EncapsulableWitness w) f) ff $ preprocPres<$>p
+preprocPres (Encaps GriddedBlocks ff p)
            = Styling grids
+           . fmap ff
            . divClass gridClass
-           . fmap (backonstruct . map (first (read . Txt.unpack . _hchunkCSSClass) . swap)
+           . Encaps ManualCSSClasses (backonstruct . map (first (read . Txt.unpack . _hchunkCSSClass) . swap)
                       . runWriterT)
-           . Encaps ManualCSSClasses
            $ preprocPres <$> layouted
  where (GridLayout w h prelayed, backonstruct) = layoutGridP p
        layouted = WriterT $ swap . first (HTMDiv . ("autogrid-range_"<>) . idc)
@@ -255,17 +286,20 @@
 preprocPres (Pure x) = Pure x
 preprocPres (Deterministic f p) = Deterministic f $ preprocPres p
 preprocPres (Interactive p a) = Interactive (preprocPres p) a
+preprocPres (Feedback f) = Feedback $ preprocPres . f
 preprocPres (Dependent d o) = Dependent (preprocPres d) (preprocPres<$>o)
 
 
 isInline :: IPresentation m a -> Bool
 isInline (StaticContent _) = True
-isInline (Encaps ManualCSSClasses (WriterT qs)) = all (\(_,i) -> case i of
+isInline (TweakableInput _ _) = False
+isInline (Encaps ManualCSSClasses _ (WriterT qs)) = all (\(_,i) -> case i of
                    HTMSpan _ -> True
                    HTMDiv _ -> False ) qs
-isInline (Encaps _ _) = False
+isInline (Encaps _ _ _) = False
 isInline (Styling _ q) = isInline q
 isInline (Interactive q _) = isInline q
+isInline (Feedback f) = False
 isInline (Resultless q) = isInline q
 isInline (Dependent q _) = isInline q
 isInline (Deterministic _ q) = isInline q
@@ -293,16 +327,26 @@
                             (WidgetT PresentationServer IO) (These Presentation r)
        chooseSlide _ _ "" Nothing Nothing (StaticContent conts)
            = pure $ These (StaticContent conts) ()
+       chooseSlide path choiceName pdiv Nothing Nothing (TweakableInput defV frm) = do
+           let (leafNm, interactor) = frm path
+               fullPath = path<>leafNm
+           storedValue <- lookupProgress fullPath
+           let (action, contents) = interactor storedValue
+           toWidget . action =<< ask
+           pure $ case (defV, storedValue) of
+             (Nothing, Nothing) -> This $ StaticContent contents
+             (_, Just r)  -> These (StaticContent contents) (Just r)
+             (Just r, _)  -> These (StaticContent contents) (Just r)
        chooseSlide path choiceName "" Nothing Nothing (Styling sty conts)
                      = mapM_ toWidget sty
                         >> chooseSlide path choiceName "" Nothing Nothing conts
-       chooseSlide path choiceName "" Nothing Nothing (Encaps f conts)
+       chooseSlide path choiceName "" Nothing Nothing (Encaps f ff conts)
                   = postGather <$> cellwise f
         where postGather sq = case sequence sq of
-               That p's -> That p's
-               This _   -> This . discardResult $ Encaps f
+               That p's -> That $ ff p's
+               This _   -> This $ Encaps f (const())
                                 $ fmap (maybe mempty id . (^?here)) sq
-               These _ p's -> (`These`p's) . discardResult $ Encaps f
+               These _ p's -> (`These`ff p's) $ Encaps f (const())
                                 $ fmap (maybe mempty id . (^?here)) sq
               cellwise ManualCSSClasses
                 | WriterT contsL <- conts
@@ -317,6 +361,11 @@
            case purity ^? here of
              Just pres -> pure . This $ discardResult pres
              Nothing   -> That <$> liftIO followAction
+       chooseSlide path choiceName pdiv bwd fwd (Feedback conts) = do
+           prefetch <- chooseSlide path choiceName pdiv bwd fwd $ conts Nothing
+           case prefetch ^? there of
+             Just v -> chooseSlide path choiceName pdiv bwd fwd . conts $ Just v
+             Nothing   -> pure prefetch
        chooseSlide path choiceName "" Nothing Nothing (Resultless conts) = do
            purity <- chooseSlide path choiceName "" Nothing Nothing conts
            case purity ^? here of
@@ -346,43 +395,45 @@
                  = maybe "false" (const "true") <$> [bwd,fwd] :: [Text]
               [previous,next] = maybe "null" id <$> [bwd, fwd]
           toWidget [julius|
-                 $("#{rawJS newPath}").click(function(e){
-                     if (e.ctrlKey && #{rawJS revertPossible}) {
-                         isRevert = true;
-                         pChanger = "@{ChPosR pPosition (PositionChange previous True)}";
-                     } else if (!(e.ctrlKey) && #{rawJS progressPossible}) {
-                         isRevert = false;
-                         pChanger = "@{ChPosR pPosition (PositionChange next False)}";
-                     } else {
-                         return;
-                     }
-                     e.stopPropagation();
-                     hasErrored = false;
-                     $.ajax({
-                           contentType: "application/json",
-                           processData: false,
-                           url: pChanger,
-                           type: "GET",
-                           dataType: "text",
-                           success: function(newURL, textStatus, jqXHR) {
-                              if (isRevert) {
-                                 window.location.replace(newURL);
-                              } else {
-                                 window.location.href = newURL;
-                              }
-                           },
-                           error: function(jqXHR, textStatus, errorThrown) {
-                              $("body").css("cursor","not-allowed");
-                              hasErrored = true;
-                              setTimeout(function() {
-                                 $("body").css("cursor","auto")}, 500);
-                           }
-                        });
-                     setTimeout(function() {
-                         if (!hasErrored) {$("body").css("cursor","wait")}
-                     }, 150);
-                 })
-               |]
+             $("#{rawJS newPath}").click(function(e){
+                 if (e.ctrlKey && #{rawJS revertPossible}) {
+                     isRevert = true;
+                     pChanger =
+                      "@{ChPosR pPosition (PositionChange previous PositionRevert)}";
+                 } else if (!(e.ctrlKey) && #{rawJS progressPossible}) {
+                     isRevert = false;
+                     pChanger =
+                      "@{ChPosR pPosition (PositionChange next PositionAdvance)}";
+                 } else {
+                     return;
+                 }
+                 e.stopPropagation();
+                 hasErrored = false;
+                 $.ajax({
+                       contentType: "application/json",
+                       processData: false,
+                       url: pChanger,
+                       type: "GET",
+                       dataType: "text",
+                       success: function(newURL, textStatus, jqXHR) {
+                          if (isRevert) {
+                             window.location.replace(newURL);
+                          } else {
+                             window.location.href = newURL;
+                          }
+                       },
+                       error: function(jqXHR, textStatus, errorThrown) {
+                          $("body").css("cursor","not-allowed");
+                          hasErrored = true;
+                          setTimeout(function() {
+                             $("body").css("cursor","auto")}, 500);
+                       }
+                    });
+                 setTimeout(function() {
+                     if (!hasErrored) {$("body").css("cursor","wait")}
+                 }, 150);
+             })
+            |]
           (here %~ spanClass thisChoice)
                   <$> chooseSlide newPath (disambiguateChoiceName choiceName)
                            "" Nothing Nothing pres
@@ -397,26 +448,26 @@
        go lvl (Resultless conts) = go lvl conts
        go lvl (Interactive conts _) = go lvl conts
        go lvl (Styling sty conts) = go lvl conts
-       go lvl (Encaps (WithHeading h) conts)
+       go lvl (Encaps (WithHeading h) ff conts)
            = let lvl' = min 6 $ lvl + 1
                  hh = [HTM.h1, HTM.h2, HTM.h3, HTM.h4, HTM.h5, HTM.h6]!!lvl
              in go lvl' $ Encaps (CustomEncapsulation (EncapsulableWitness SessionableWitness)
                                          $ \(Identity contsr)
                                     -> HTM.div HTM.! HTM.class_ "headed-container"
                                          $ hh h <> contsr
-                                 ) conts
-       go lvl (Encaps ManualCSSClasses conts)
+                                 ) ff conts
+       go lvl (Encaps ManualCSSClasses ff conts)
            = go lvl $ Encaps (CustomEncapsulation (EncapsulableWitness SessionableWitness) $ \(WriterT contsrs)
                   -> foldMap (\(q,i) -> case i of
                                HTMDiv c -> [hamlet| <div class=#{withSupclass c}> #{q} |]()
                                HTMSpan c -> [hamlet| <span class=#{withSupclass c}> #{q} |]())
                       $ contsrs
-                 ) conts
+                 ) ff conts
         where withSupclass c
                | Just _ <- Txt.stripPrefix "autogrid_" c
                             = "autogrid "<>c
                | otherwise  = c
-       go lvl (Encaps (CustomEncapsulation (EncapsulableWitness _) f) conts) = f $ go lvl <$> conts
+       go lvl (Encaps (CustomEncapsulation (EncapsulableWitness _) f) _ conts) = f $ go lvl <$> conts
        go _ p = error $ outerConstructorName p <> " cannot be rendered."
 
 
@@ -431,59 +482,86 @@
 
 instance (Monoid r, Sessionable r) => SG.Semigroup (IPresentation m r) where
   StaticContent c <> StaticContent d = StaticContent $ c<>d
-  Encaps ManualCSSClasses (WriterT elems₀) <> Encaps ManualCSSClasses (WriterT elems₁)
-     = Encaps ManualCSSClasses . WriterT . disambiguate $ elems₀ ++ elems₁
+  Encaps ManualCSSClasses ff₀ (WriterT elems₀) <> Encaps ManualCSSClasses ff₁ (WriterT elems₁)
+     = Encaps ManualCSSClasses ff' . WriterT . disambiguate
+           $ map (first $ fmap Left) elems₀ ++ map (first $ fmap Right) elems₁
    where disambiguate = go 0 Map.empty
           where go _ _ [] = []
                 go i occupied ((q,c):qs)
                  | Txt.null (_hchunkCSSClass c) || c`Map.member`occupied
                     = let c' = c & hchunkCSSClass .~ Txt.pack ("anonymousCell-"++show i)
-                      in go (i+1) occupied (( fmap (fst . head . runWriterT)
-                                             . Encaps ManualCSSClasses $ WriterT [(q,c)]
+                      in go (i+1) occupied (( Encaps ManualCSSClasses (fst . head . runWriterT) $ WriterT [(q,c)]
                                             , c' ):qs)
                  | otherwise
                     = (q,c) : go (i+1) (Map.insert c () occupied) qs
-  Resultless (Encaps ManualCSSClasses ps) <> Resultless (Encaps ManualCSSClasses qs)
-      = Resultless $ Encaps ManualCSSClasses (discardResult<$>ps)
-               SG.<> Encaps ManualCSSClasses (discardResult<$>qs)
-  Resultless p@(Encaps ManualCSSClasses _) <> c
-      = Resultless p <> Resultless (Encaps ManualCSSClasses $ WriterT [(c,hchunkFor""c)])
-  c <> Resultless p@(Encaps ManualCSSClasses _)
-      = Resultless (Encaps ManualCSSClasses $ WriterT [(c,hchunkFor""c)]) <> Resultless p
-  p <> q = fmap fold . Encaps ManualCSSClasses $ WriterT
+         ff' (WriterT l) = case partitionEithers
+                             $ map ( \(d,r)->case d of Left d'->Left (d',r)
+                                                       Right d'->Right (d',r) ) l of
+                  (l₀,l₁) -> ff₀ (WriterT l₀)<>ff₁ (WriterT l₁)
+  Resultless (Encaps ManualCSSClasses _ ps) <> Resultless (Encaps ManualCSSClasses _ qs)
+      = Resultless $ Encaps ManualCSSClasses id (discardResult<$>ps)
+               SG.<> Encaps ManualCSSClasses id (discardResult<$>qs)
+  Resultless p@(Encaps ManualCSSClasses _ _) <> c
+      = Resultless p <> Resultless (Encaps ManualCSSClasses id $ WriterT [(c,hchunkFor""c)])
+  c <> Resultless p@(Encaps ManualCSSClasses _ _)
+      = Resultless (Encaps ManualCSSClasses id $ WriterT [(c,hchunkFor""c)]) <> Resultless p
+  p <> q = Encaps ManualCSSClasses fold $ WriterT
              [(p, hchunkFor"anonymousCell-0"p), (q, hchunkFor"anonymousCell-1"q)]
 instance ∀ m . Monoid (IPresentation m ()) where
   mappend = (SG.<>)
-  mempty = Resultless $ Encaps ManualCSSClasses
+  mempty = Resultless $ Encaps ManualCSSClasses id
                 (WriterT [] :: WriterT HTMChunkK [] (IPresentation m ()))
 
+infix 6 →│
+(→│) :: (Sessionable a)
+    => IPresentation m a -> IPresentation m b -> IPresentation m a
+l→│r = fmap (\(GridDivisions [[GridRegion (Just a), GridRegion Nothing]]) -> a)
+       . Encaps GriddedBlocks id
+       $ GridDivisions [GridRegion<$>[ Just<$>l, const Nothing<$>r ]]
+
+infix 6 →│→
+(→│→) :: (Sessionable a)
+    => IPresentation m a -> (a -> IPresentation m ()) -> IPresentation m a
+l→│→r = Feedback $ \aFbq -> l →│ case aFbq of
+                                  Just a -> r a
+                                  othing -> mempty
+
+infix 6 →│←
+(→│←) :: (Sessionable a, Sessionable b)
+    => IPresentation m a -> IPresentation m b -> IPresentation m (a,b)
+l→│←r = fmap (\(GridDivisions [[GridRegion (Left a), GridRegion (Right b)]])
+                 -> (a,b))
+       . Encaps GriddedBlocks id
+       $ GridDivisions [GridRegion<$>[Left<$>l, Right<$>r]]
+
 instance ∀ m . SemigroupNo 0 (IPresentation m ()) where
-  sappendN _ (Resultless (Encaps GriddedBlocks l))
-             (Resultless (Encaps GriddedBlocks r))
-           = Resultless . Encaps GriddedBlocks $ (discardResult<$>l) │ (discardResult<$>r)
-  sappendN _ l@(Resultless (Encaps GriddedBlocks _)) r
-           = l │ Resultless (Encaps GriddedBlocks $ pure r)
+  sappendN _ (Resultless (Encaps GriddedBlocks _ l))
+             (Resultless (Encaps GriddedBlocks _ r))
+           = Resultless . Encaps GriddedBlocks id $ (discardResult<$>l) │ (discardResult<$>r)
+  sappendN _ l@(Resultless (Encaps GriddedBlocks _ _)) r
+           = l │ Resultless (Encaps GriddedBlocks id $ pure r)
   sappendN _ l r
-           = Resultless (Encaps GriddedBlocks $ pure l) │ r
+           = Resultless (Encaps GriddedBlocks id $ pure l) │ r
 
 instance ∀ m . SemigroupNo 1 (IPresentation m ()) where
-  sappendN _ (Resultless (Encaps GriddedBlocks t))
-             (Resultless (Encaps GriddedBlocks b))
-           = Resultless . Encaps GriddedBlocks $ (discardResult<$>t) ── (discardResult<$>b)
-  sappendN _ t@(Resultless (Encaps GriddedBlocks _)) b
-           = t ── Resultless (Encaps GriddedBlocks $ pure b)
+  sappendN _ (Resultless (Encaps GriddedBlocks _ t))
+             (Resultless (Encaps GriddedBlocks _ b))
+           = Resultless . Encaps GriddedBlocks id $ (discardResult<$>t) ── (discardResult<$>b)
+  sappendN _ t@(Resultless (Encaps GriddedBlocks _ _)) b
+           = t ── Resultless (Encaps GriddedBlocks id $ pure b)
   sappendN _ t b
-           = Resultless (Encaps GriddedBlocks $ pure t) ── b
+           = Resultless (Encaps GriddedBlocks id $ pure t) ── b
 
 
 outerConstructorName :: IPresentation m r -> String
 outerConstructorName (StaticContent _) = "StaticContent"
+outerConstructorName (TweakableInput _ _) = "TweakableInput"
 outerConstructorName (Resultless _) = "Resultless"
 outerConstructorName (Styling _ _) = "Styling"
-outerConstructorName (Encaps (WithHeading _) _) = "Encaps WithHeading"
-outerConstructorName (Encaps (CustomEncapsulation _ _) _) = "Encaps CustomEncapsulation"
-outerConstructorName (Encaps ManualCSSClasses _) = "Encaps ManualCSSClasses"
-outerConstructorName (Encaps GriddedBlocks _) = "Encaps GriddedBlocks"
+outerConstructorName (Encaps (WithHeading _) _ _) = "Encaps WithHeading"
+outerConstructorName (Encaps (CustomEncapsulation _ _) _ _) = "Encaps CustomEncapsulation"
+outerConstructorName (Encaps ManualCSSClasses _ _) = "Encaps ManualCSSClasses"
+outerConstructorName (Encaps GriddedBlocks _ _) = "Encaps GriddedBlocks"
 outerConstructorName (Pure _) = "Pure"
 outerConstructorName (Deterministic _ _) = "Deterministic"
 outerConstructorName (Interactive _ _) = "Interactive"
@@ -494,6 +572,9 @@
 discardResult (Resultless p) = Resultless p
 discardResult p = Resultless p
 
+feedback_ :: Sessionable a => (Maybe a -> IPresentation m a) -> IPresentation m ()
+feedback_ = discardResult . Feedback
+
 serverSide :: Sessionable a => m a -> IPresentation m a
 serverSide = Interactive (pure ())
 
@@ -510,33 +591,36 @@
 instance ∀ m . Monad (IPresentation m) where
   return = pure
   StaticContent c >>= f = Dependent (StaticContent c) f
+  TweakableInput defV frm >>= f = Dependent (TweakableInput defV frm) f
   Resultless p >>= f = Dependent (Resultless p) f
+  Feedback p >>= f = Dependent (Feedback p) f
   Styling _ (Pure x) >>= f = f x
   Styling s (StaticContent c) >>= f = Dependent (Styling s (StaticContent c)) f
   Styling s (Resultless c) >>= f = Dependent (Styling s (Resultless c)) f
   Styling s (Styling s' x) >>= f = Styling (s++s') x >>= f
-  Styling s (Encaps (WithHeading h) x) >>= f
-      = Dependent (Styling s (Encaps (WithHeading h) x)) f
-  Styling s (Encaps ManualCSSClasses x) >>= f
-      = Dependent (Styling s (Encaps ManualCSSClasses x)) f
+  Styling s (Encaps (WithHeading h) ff x) >>= f
+      = Dependent (Styling s (Encaps (WithHeading h) ff x)) f
+  Styling s (Encaps ManualCSSClasses ff x) >>= f
+      = Dependent (Styling s (Encaps ManualCSSClasses ff x)) f
   Styling s (Deterministic g x) >>= f = Styling s x >>= f . g
   Styling s (Interactive p o) >>= f = Dependent (Interactive (Styling s p) o) f
   Styling s (Dependent p g) >>= f = Dependent (Styling s p) $ Styling s . g >=> f
-  Encaps (WithHeading h) p >>= f = Dependent (Encaps (WithHeading h) p) f
-  Encaps ManualCSSClasses ps >>= f = Dependent (Encaps ManualCSSClasses ps) f
-  Encaps (CustomEncapsulation (EncapsulableWitness w') e') ps' >>= f'
-      = bindCustEncaps w' e' ps' f'
-   where bindCustEncaps :: ∀ a b t r
-                        . (Sessionable r, Traversable t, Sessionable (t ()))
-                        => (∀ r' . Sessionable r' => SessionableWitness (t r'))
-                        -> (t Html -> Html)
-                        -> t (IPresentation m r)
-                        -> (t r -> IPresentation m b)
-                        -> IPresentation m b
-         bindCustEncaps w e ps f
+  Encaps (WithHeading h) ff p >>= f = Dependent (Encaps (WithHeading h) ff p) f
+  Encaps ManualCSSClasses ff ps >>= f = Dependent (Encaps ManualCSSClasses ff ps) f
+  Encaps (CustomEncapsulation (EncapsulableWitness w') e') ff' ps' >>= f'
+      = bindCustEncaps w' e' ff' ps' f'
+   where bindCustEncaps :: ∀ a b t r tr
+                   . (Sessionable r, Sessionable tr, Traversable t, Sessionable (t ()))
+                   => (∀ r' . Sessionable r' => SessionableWitness (t r'))
+                   -> (t Html -> Html)
+                   -> (t r -> tr)
+                   -> t (IPresentation m r)
+                   -> (tr -> IPresentation m b)
+                   -> IPresentation m b
+         bindCustEncaps w e ff ps f
           = case w :: SessionableWitness (t r) of
              SessionableWitness
-               -> Dependent (Encaps (CustomEncapsulation (EncapsulableWitness w) e) ps) f
+               -> Dependent (Encaps (CustomEncapsulation (EncapsulableWitness w) e) ff ps) f
   Pure x >>= f = f x
   Deterministic g p >>= f = p >>= f . g
   Interactive p q >>= f = Dependent (Interactive p q) f
@@ -553,19 +637,16 @@
 (======) = addHeading
 
 addHeading :: Sessionable r => Html -> IPresentation m r -> IPresentation m r
-addHeading h = fmap runIdentity . Encaps (WithHeading h) . Identity
+addHeading h = Encaps (WithHeading h) runIdentity . Identity
 
 divClass :: Sessionable r => Text -> IPresentation m r -> IPresentation m r
-divClass cn = fmap (fst . head . runWriterT)
-              . Encaps ManualCSSClasses . WriterT . pure . (,HTMDiv cn)
+divClass cn = Encaps ManualCSSClasses (fst . head . runWriterT) . WriterT . pure . (,HTMDiv cn)
 
 spanClass :: Sessionable r => Text -> IPresentation m r -> IPresentation m r
-spanClass cn = fmap (fst . head . runWriterT)
-              . Encaps ManualCSSClasses . WriterT . pure . (,HTMSpan cn)
+spanClass cn = Encaps ManualCSSClasses (fst . head . runWriterT) . WriterT . pure . (,HTMSpan cn)
 
 divClasses :: Sessionable r => [(Text, IPresentation m r)] -> IPresentation m r
-divClasses cns = fmap (fst . head . runWriterT)
-              . Encaps ManualCSSClasses $ WriterT [ (content,HTMDiv cn)
+divClasses cns = Encaps ManualCSSClasses (fst . head . runWriterT) $ WriterT [ (content,HTMDiv cn)
                                                   | (cn,content) <- cns ]
 
 infix 8 #%
@@ -584,11 +665,72 @@
 staticContent = fmap (const mempty) . StaticContent
 
 tweakContent :: Sessionable r => (Html -> Html) -> IPresentation m r -> IPresentation m r
-tweakContent f = fmap runIdentity
-               . Encaps (CustomEncapsulation (EncapsulableWitness SessionableWitness)
-                              $ f . runIdentity)
+tweakContent f = Encaps (CustomEncapsulation (EncapsulableWitness SessionableWitness)
+                              $ f . runIdentity) runIdentity
                . Identity
 
+class Sessionable i => Inputtable i where
+  inputElemHtml :: i      -- ^ Current value
+                -> String -- ^ id in the DOM
+                -> Html
+
+instance Inputtable Int where
+  inputElemHtml currentVal hashedId = [hamlet|
+        <input type="number" id="#{hashedId}" value=#{currentVal}>
+       |]()
+
+instance Inputtable Double where
+  inputElemHtml currentVal hashedId = [hamlet|
+        <input type="number" id="#{hashedId}" value=#{currentVal} step="any">
+       |]()
+
+inputBox :: (Inputtable i, JSON.FromJSON i) => i -> IPresentation m i
+inputBox iDef = fmap (maybe iDef id) . TweakableInput (Just iDef) $ \path ->
+      let hashedId = base64md5 . BSL.fromStrict $ Txt.encodeUtf8 path
+          inputElId = "input#"++hashedId
+      in ( leafNm
+         , \prevInp ->
+            let currentVal = case prevInp of
+                 Nothing -> iDef
+                 Just v -> v
+            in ( \pPosition -> [julius|
+                 $("#{rawJS inputElId}").click(function(e){
+                     e.stopPropagation();
+                   })
+                 $("#{rawJS inputElId}").change(function(e){
+                     currentVal = $("#{rawJS inputElId}").val()
+                     pChanger =
+                          "@{SetValR pPosition path NoValGiven}".slice(0, -1)
+                                // The slice hack removes the `NoValGiven`, to
+                                // be replaced with the actual value:
+                          + currentVal;
+                     e.stopPropagation();
+                     hasErrored = false;
+                     $.ajax({
+                           contentType: "application/json",
+                           processData: false,
+                           url: pChanger,
+                           type: "GET",
+                           dataType: "text",
+                           success: function(newURL, textStatus, jqXHR) {
+                              window.location.href = newURL;
+                           },
+                           error: function(jqXHR, textStatus, errorThrown) {
+                              $("body").css("cursor","not-allowed");
+                              hasErrored = true;
+                              setTimeout(function() {
+                                 $("body").css("cursor","auto")}, 500);
+                           }
+                        });
+                     setTimeout(function() {
+                         if (!hasErrored) {$("body").css("cursor","wait")}
+                     }, 150);
+                 })
+                      |]
+               , inputElemHtml currentVal hashedId
+               ) )
+ where leafNm = " input"
+
 infixr 6 $<>
 ($<>) :: (r ~ (), TMM.SymbolClass σ, TMM.SCConstraint σ LaTeX)
          => TMM.CAS (TMM.Infix LaTeX) (TMM.Encapsulation LaTeX) (TMM.SymbolD σ LaTeX)
@@ -601,10 +743,18 @@
 maths eqns = renderTeXMaths MathML.DisplayBlock . TMM.maths eqns
 
 renderTeXMaths :: MathML.DisplayType -> LaTeX -> IPresentation m ()
-renderTeXMaths dispSty tex = case MathML.readTeX . Txt.unpack $ LaTeX.render tex of
+renderTeXMaths dispSty tex = case MathML.readTeX
+#if !MIN_VERSION_texmath(0,12,0)
+                                   . Txt.unpack
+#endif
+                                   $ LaTeX.render tex of
          Right exps -> StaticContent . HTM.preEscapedText . Txt.pack . XML.showElement
                         $ MathML.writeMathML dispSty exps
-         Left err -> error $ "Failed to re-parse generated LaTeX. "++err
+         Left err -> error $ "Failed to re-parse generated LaTeX. "++
+#if MIN_VERSION_texmath(0,12,0)
+                               Txt.unpack
+#endif
+                                 err
 
 -- | Include a piece of plaintext, preserving all formatting. To be used in an
 --   oxford bracket.
@@ -631,7 +781,7 @@
          | otherwise  = preescapeInline s
        preescapeBlock s = intercalate "<br>" $ drop zeroIndent <$> sLines
         where zeroIndent = minimum $ length . takeWhile (==' ') <$> sLines
-              sLines = lines s
+              sLines = preescapeInline <$> lines s
        preescapeInline = concatMap preescapeChar
        preescapeChar '<' = "&lt;"
        preescapeChar '>' = "&gt;"
@@ -733,13 +883,17 @@
          CustomFile use -> use servableFile
 
 
+getSetValR :: PresProgress -> PrPath -> ValueToSet -> Handler Text
+getSetValR oldPosition path
+    = getChPosR oldPosition . PositionChange path . PositionSetValue
+
 getChPosR :: PresProgress -> PositionChange -> Handler Text
 getChPosR oldPosition posStep = do
    newPosition <- execStateT (changePos_State posStep) oldPosition
    toTextUrl $ ExactPositionR newPosition
 
 changePos_State :: PositionChange -> StateT PresProgress Handler ()
-changePos_State (PositionChange path isRevert) = do
+changePos_State (PositionChange path pChangeKind) = do
     PresentationServer presentation _ _ <- getYesod
     go ("", defaultChoiceName, "") (finePath <$> Txt.words path) presentation
     return ()
@@ -756,17 +910,34 @@
                            ( Maybe r  -- Key value this branch yields
                            , Bool )   -- Whether it contains displayable content
        go _ [] (StaticContent _) = return $ (Just (), True)
+       go (crumbh,choiceName,crumbp) [] (TweakableInput defV twInp) = do
+          let (pathFin, _) = twInp crumbh
+              fullPath = crumbh<>pathFin
+          case pChangeKind of
+           PositionSetValue (ValueToSet newVal)
+            -> case JSON.fromJSON newVal of
+              JSON.Success v -> do
+               setProgress fullPath v
+               return (Just $ Just v, True)
+              JSON.Error e -> fail e
+           _ -> do
+             key <- lookupProgress fullPath
+             let result = case (key, defV) of
+                  (Just v, _) -> Just v
+                  (_, Just v) -> Just v
+                  (Nothing, Nothing) -> Nothing
+             return $ (Just result, True)
        go _ [] (Pure x) = return $ (Just x, False)
        go _ [] (Interactive _ q)
            = (,error "Don't know if interactive request actually shows something.")
              . Just <$> liftIO q
-       go crumbs path (Encaps (WithHeading _) (Identity cont))
-           = (,True) . fmap Identity . fst <$> go crumbs path cont
-       go crumbs path (Encaps (CustomEncapsulation _ _) cont)
-           = (,True) . sequence
+       go crumbs path (Encaps (WithHeading _) ff (Identity cont))
+           = (,True) . fmap (ff . Identity) . fst <$> go crumbs path cont
+       go crumbs path (Encaps (CustomEncapsulation _ _) ff cont)
+           = (,True) . fmap ff . sequence
               <$> traverse (\c -> fst <$> go crumbs path c) cont
-       go (crumbh,choiceName,crumbp) [] (Encaps ManualCSSClasses (WriterT conts))
-           = (,True) . sequence . WriterT <$> traverse
+       go (crumbh,choiceName,crumbp) [] (Encaps ManualCSSClasses ff (WriterT conts))
+           = (,True) . fmap ff . sequence . WriterT <$> traverse
                 (\(c,ζ) -> (,ζ) . fst <$> go (crumbh<>case ζ of
                                               HTMDiv i -> " div."<>i
                                               HTMSpan i -> " span."<>i
@@ -776,23 +947,24 @@
        go crumbs [] (Resultless c) = (Just (),) <$> hasDisplayableContent crumbs c
        go crumbs path (Resultless c) = first (const $ Just()) <$> go crumbs path c
        go crumbs path (Interactive p _) = first (const Nothing) <$> go crumbs path p
+       go crumbs path (Feedback p) = go crumbs path $ p Nothing
        go (crumbh, choiceName, crumbp) (('0':prog):path') (Dependent def _)
            = first (const Nothing)
                 <$> go' (crumbh, choiceName, crumbp<>"0") (prog:path') def
        go (crumbh, choiceName, crumbp) path' (Dependent def opt) = do
           key <- lookupProgress $ crumbh <> " span."<>choiceName crumbp
-          case (key, path', isRevert) of
+          case (key, path', pChangeKind) of
             (Just k, ('1':prog):path'', _) -> do
               (resKey, rHasContent)
                    <- go' (crumbh, choiceName, crumbp<>"1") (prog:path'') $ opt k
-              if isRevert && not rHasContent then do
+              if pChangeKind==PositionRevert && not rHasContent then do
                  revertProgress $ crumbh <> " span."<>choiceName crumbp
                  return (Nothing, False)
                else return (resKey, rHasContent)
             (Nothing, ('1':prog):path'', _) -> do
               (~(Just k), _) <- go' (crumbh, choiceName, crumbp<>"0") [] def
               go' (crumbh, choiceName, crumbp<>"1") (prog:path'') $ opt k
-            (_, [[]], False) -> do
+            (_, [[]], PositionAdvance) -> do
               (key', _) <- go' (crumbh,choiceName,crumbp<>"0") [[]] def
               case key' of
                Just k -> do
@@ -800,23 +972,23 @@
                  skipContentless (crumbh, choiceName, crumbp<>"1") $ opt k
                  return (Nothing, True)
                Nothing -> error $ outerConstructorName def ++ " refuses to yield a result value."
-            (_, [[]], True) -> do
+            (_, [[]], PositionRevert) -> do
               revertProgress path
               lHasContent
                     <- hasDisplayableContent (crumbh, choiceName, crumbp<>"0") def
               return (Nothing, lHasContent)
-            (Just k, [], False)
+            (Just k, [], PositionAdvance)
              -> go' (crumbh, choiceName, crumbp<>"1") [] $ opt k
-            (Nothing, [], False)
+            (Nothing, [], PositionAdvance)
              -> return (Nothing, False)
             (_, dir:_, _)
              -> error $ "Div-ID "++dir++" not suitable for making a Dependent choice."
        go crumbs path (Styling _ cont) = go crumbs path cont
-       go (crumbh, choiceName, _) (divid:path) (Encaps ManualCSSClasses (WriterT conts))
+       go (crumbh, choiceName, _) (divid:path) (Encaps ManualCSSClasses ff (WriterT conts))
          | Just dividt <-  HTMDiv<$>Txt.stripPrefix "div." (Txt.pack divid)
                        <|> HTMSpan<$>Txt.stripPrefix "span." (Txt.pack divid)
          , Just subSel <- lookup dividt $ swap<$>conts
-              = first (fmap $ WriterT . pure . (,dividt))
+              = first (fmap $ ff . WriterT . pure . (,dividt))
                   <$> go (crumbh<>case dividt of
                                  HTMDiv i -> " div."<>i
                                  HTMSpan i -> " span."<>i
@@ -864,7 +1036,7 @@
        skipContentless crumbs (Deterministic f c)
            = fmap f <$> skipContentless crumbs c
        skipContentless _ (StaticContent _) = return Nothing
-       skipContentless _ (Encaps _ _) = return Nothing
+       skipContentless _ (Encaps _ _ _) = return Nothing
        skipContentless _ p = error
         $ "`skipContentless` does not support "++outerConstructorName p
 
@@ -886,7 +1058,7 @@
        hasDisplayableContent crumbs (Deterministic f c)
            = hasDisplayableContent crumbs c
        hasDisplayableContent _ (StaticContent _) = return True
-       hasDisplayableContent _ (Encaps _ _) = return True
+       hasDisplayableContent _ (Encaps _ _ _) = return True
        hasDisplayableContent _ p = error
         $ "`hasDisplayableContent` does not support "++outerConstructorName p
 
@@ -910,7 +1082,7 @@
 
 
 class (MonadHandler m) => KnowsProgressState m where
-  lookupProgress :: Flat x => PrPath -> m (Maybe x)
+  lookupProgress :: (HasCallStack, Flat x) => PrPath -> m (Maybe x)
 
 instance MonadHandler m
             => KnowsProgressState (StateT PresProgress m) where
@@ -963,3 +1135,149 @@
 --   in a web browser, on port 14910. This is a shorthand for @'yeamer'' 'def'@.
 yeamer :: Presentation -> IO ()
 yeamer = yeamer' def
+
+
+
+data DisplayOrientation = DisplayHorizontally | DisplayVertically
+  deriving (Eq, Show, Generic)
+otherDisplayOrientation :: DisplayOrientation -> DisplayOrientation
+otherDisplayOrientation DisplayHorizontally = DisplayVertically
+otherDisplayOrientation DisplayVertically = DisplayHorizontally
+
+class InteractiveShow a where
+  display :: a -> Presentation
+  display = displayOriented DisplayHorizontally
+  displayOriented :: DisplayOrientation -> a -> Presentation
+  default displayOriented :: (Generic a, GInteractiveShow (Rep a))
+              => DisplayOrientation -> a -> Presentation
+  displayOriented orient = gDisplayOriented orient . from
+  displayList :: DisplayOrientation -> [a] -> Presentation
+  displayList orient = go 1
+   where go _ [] = "[]"
+         go n xs = case splitAt (sum [1..n]) xs of
+           (l₀:r@(_:_),[])
+               -> let m = init r; ω = last r
+                  in foldr1 catOp $ ["["│display' l₀│" "]
+                                 ++ map ((","│).(│" ").display') m
+                                 ++ [","│display' ω│"]"]
+           (l,[])
+               -> "[" │ foldr1 (│) (display'<$>l) │ "]"
+           (l₀:r@(_:_),_)
+               -> (let m = init r; ω = last r
+                   in foldr1 catOp $ ["("│display' l₀]
+                                  ++ map ((":"│).display') m
+                                  ++ [ ":"│display' ω
+                                     , ":"│"...)" ]
+                    ) >>= \() -> go (n + 1) xs
+           (l,_) -> "(" │ foldr1 (│) (display'<$>l) │ ":" │ "..." │ ")"
+                      >>= \() -> go (n + 1) xs
+         catOp = case orient of
+          DisplayHorizontally -> (│)
+          DisplayVertically -> (──)
+         display' = displayOriented $ otherDisplayOrientation orient
+
+class GInteractiveShow f where
+  gDisplayOriented :: DisplayOrientation -> f p -> Presentation
+
+instance InteractiveShow Char where
+  displayOriented _ c = fromString $ show c
+  displayList _ s = fromString $ show s
+instance InteractiveShow Int where displayOriented _ s = fromString $ show s
+instance InteractiveShow Int64 where displayOriented _ s = fromString $ show s
+instance InteractiveShow Int32 where displayOriented _ s = fromString $ show s
+instance InteractiveShow Int16 where displayOriented _ s = fromString $ show s
+instance InteractiveShow Double where
+  displayOriented _ x
+    | fromIntegral rounded == x   = display rounded
+    | read imprecise == x         = fromString imprecise
+    | otherwise = do
+        approxShw
+        fromString $ show x
+   where rounded = round x :: Int16
+         imprecise = printf "%.1g" x
+         approxShw = case break (=='e') imprecise of
+           (man,ex) -> fromString $ man ++ "…" ++ ex
+instance InteractiveShow a => InteractiveShow [a] where
+  displayOriented = displayList
+
+
+instance GInteractiveShow V1 where
+  gDisplayOriented _ a = case a of {}
+instance GInteractiveShow U1 where
+  gDisplayOriented _ _ = mempty
+instance (GInteractiveShow l, GInteractiveShow r) => GInteractiveShow (l:+:r) where
+  gDisplayOriented orient (L1 x) = gDisplayOriented orient x
+  gDisplayOriented orient (R1 y) = gDisplayOriented orient y
+instance (GInteractiveShow l, GInteractiveShow r) => GInteractiveShow (l:*:r) where
+  gDisplayOriented orient (x:*:y) = gDisplayOriented orient x ⊕ gDisplayOriented orient y
+   where (⊕) = case orient of DisplayHorizontally -> (│)
+                              DisplayVertically -> (──)
+instance InteractiveShow a => GInteractiveShow (K1 i a) where
+  gDisplayOriented orient (K1 x)
+        = displayOriented (otherDisplayOrientation orient) x
+
+instance GInteractiveShow f => GInteractiveShow (M1 i ('MetaData ν μ π τ) f) where
+  gDisplayOriented orient (M1 x) = dispDataEncapsulated $ gDisplayOriented orient x
+instance KnownSymbol n
+              => GInteractiveShow (M1 i ('MetaCons n φ σ) U1) where
+  gDisplayOriented orient (M1 x) = dispConstructorLabel @n
+instance (GInteractiveShow f, GInteractiveShow g, KnownSymbol n)
+              => GInteractiveShow (M1 i ('MetaCons n φ σ) (f:*:g)) where
+  gDisplayOriented orient (M1 x) = styling ([cassius|
+                  .yeamer-display-dataFields-vert>.autogrid>div
+                    border-top: 1px dashed
+                  .yeamer-display-dataFields-horiz>.autogrid>div
+                    border-left: 1px dashed
+                                             |]())
+          $ dispConstructorLabel @n
+              <> divClass ("yeamer-display-dataFields-"<>rfOrient)
+                     (gDisplayOriented orient x)
+   where rfOrient = case orient of DisplayHorizontally -> "horiz"
+                                   DisplayVertically -> "vert"
+instance (GInteractiveShow (M1 j μ f), KnownSymbol n)
+              => GInteractiveShow (M1 i ('MetaCons n φ σ)
+                                        (M1 j μ f)) where
+  gDisplayOriented orient (M1 x) = dispConstructorLabel @n
+                    ── gDisplayOriented (otherDisplayOrientation orient
+                                          -- single-field cons: undo K1 direction-change
+                                        ) x
+
+instance GInteractiveShow f
+    => GInteractiveShow (M1 i ('MetaSel 'Nothing υ σ 'DecidedStrict) f) where
+  gDisplayOriented orient (M1 x) = gDisplayOriented orient x
+instance GInteractiveShow f
+    => GInteractiveShow (M1 i ('MetaSel 'Nothing υ σ 'DecidedUnpack) f) where
+  gDisplayOriented orient (M1 x) = gDisplayOriented orient x
+instance GInteractiveShow f
+    => GInteractiveShow (M1 i ('MetaSel 'Nothing υ σ 'DecidedLazy) f) where
+  gDisplayOriented orient (M1 x) = "..." >>= \() -> gDisplayOriented orient x
+instance (GInteractiveShow f, KnownSymbol n)
+             => GInteractiveShow (M1 i ('MetaSel ('Just n) υ σ 'DecidedStrict) f) where
+  gDisplayOriented orient (M1 x)
+             = dispRecFieldLabel @n ⊕ gDisplayOriented orient x
+   where (⊕) = case orient of DisplayHorizontally -> (──)
+                              DisplayVertically -> (│)
+instance (GInteractiveShow f, KnownSymbol n)
+             => GInteractiveShow (M1 i ('MetaSel ('Just n) υ σ 'DecidedUnpack) f) where
+  gDisplayOriented orient (M1 x)
+             = dispRecFieldLabel @n ⊕ gDisplayOriented orient x
+   where (⊕) = case orient of DisplayHorizontally -> (──)
+                              DisplayVertically -> (│)
+instance (GInteractiveShow f, KnownSymbol n)
+             => GInteractiveShow (M1 i ('MetaSel ('Just n) υ σ 'DecidedLazy) f) where
+  gDisplayOriented orient (M1 x)
+    = (dispRecFieldLabel @n ⊕ "...")
+       >>= \() -> (dispRecFieldLabel @n ⊕ gDisplayOriented orient x)
+   where (⊕) = case orient of DisplayHorizontally -> (──)
+                              DisplayVertically -> (│)
+
+dispDataEncapsulated :: Presentation -> Presentation
+dispDataEncapsulated = divClass "yeamer-display-dataEncapsulation"
+
+dispConstructorLabel :: ∀ n . KnownSymbol n => Presentation
+dispConstructorLabel = divClass "yeamer-display-dataConstructorName"
+                      $ fromString (symbolVal @n Proxy)
+
+dispRecFieldLabel :: ∀ n . KnownSymbol n => Presentation
+dispRecFieldLabel = divClass "yeamer-display-recordFieldLabel"
+                      $ fromString (symbolVal @n Proxy ++ "=")
diff --git a/Presentation/Yeamer/Internal/Grid.hs b/Presentation/Yeamer/Internal/Grid.hs
--- a/Presentation/Yeamer/Internal/Grid.hs
+++ b/Presentation/Yeamer/Internal/Grid.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
@@ -24,7 +24,7 @@
 import GHC.Generics
 
 import Data.Aeson (FromJSON, ToJSON)
-import Data.Flat (Flat)
+import Flat (Flat)
 
 import Data.Ratio ((%))
 
@@ -32,6 +32,7 @@
 import Data.Ord (comparing)
 
 import Control.Applicative (liftA2)
+import Control.Monad.Trans.State
 import Control.Arrow (second)
 
 import Lens.Micro
@@ -80,25 +81,39 @@
 makeLenses ''GridLayout
 
 layoutGrid :: Gridded a -> GridLayout a
--- layoutGrid = fmap snd . fst . layoutGridP
+layoutGrid = fmap snd . fst . layoutGridP
 
 type GridRegionId = Int
 
 layoutGridP :: Gridded a -> ( GridLayout (GridRegionId, a)
                             , [(GridRegionId, b)] -> Gridded b )
-layoutGridP g = ( layoutGrid g & gridContents %~ zipWith (second . (,)) [0..]
-                , const undefined )
-
-layoutGrid (GridRegion a) = GridLayout 1 1 [(GridRange 0 1 0 1, a)]
-layoutGrid (GridDivisions []) = GridLayout 0 0 []
-layoutGrid (GridDivisions [row])
-    = alignLayoutDirectional gridWidth xBegin xEnd
+layoutGridP = (`evalState`0) . go
+ where go (GridRegion a) = do
+         i <- get
+         put $ i+1
+         return ( GridLayout 1 1 [(GridRange 0 1 0 1, (i, a))]
+                , \[(_, b)] -> GridRegion b )
+       go (GridDivisions [[GridRegion a₀, GridRegion a₁]]) = do
+         i <- get
+         put $ i+2
+         return ( GridLayout 2 1 [ (GridRange 0 1 0 1, (i, a₀))
+                                 , (GridRange 1 2 0 1, (i+1, a₁)) ]
+                , \[(_,b₀), (_,b₁)] -> GridDivisions [[GridRegion b₀,GridRegion b₁]] )
+       go (GridDivisions []) 
+        = return ( GridLayout 0 0 []
+                 , \[] -> GridDivisions [] )
+       go (GridDivisions [row]) = do
+         layouts <- mapM go row
+         return ( alignLayoutDirectional gridWidth xBegin xEnd
                              gridHeight yBegin yEnd
-                        $ layoutGrid <$> row
-layoutGrid (GridDivisions rows)
-    = alignLayoutDirectional gridHeight yBegin yEnd
+                             (fst<$>layouts)
+                , undefined )
+       go (GridDivisions rows) = do
+         rLayouts <- mapM (go . GridDivisions . pure) rows
+         return ( alignLayoutDirectional gridHeight yBegin yEnd
                              gridWidth xBegin xEnd
-                        $ layoutGrid . GridDivisions . pure <$> rows
+                        (fst<$>rLayouts)
+                , undefined )
 
 alignLayoutDirectional
     :: Lens' (GridLayout a) Int -> Lens' GridRange Int -> Lens' GridRange Int
diff --git a/Presentation/Yeamer/Internal/PrPathStepCompression.hs b/Presentation/Yeamer/Internal/PrPathStepCompression.hs
--- a/Presentation/Yeamer/Internal/PrPathStepCompression.hs
+++ b/Presentation/Yeamer/Internal/PrPathStepCompression.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
diff --git a/Presentation/Yeamer/Internal/Progress.hs b/Presentation/Yeamer/Internal/Progress.hs
--- a/Presentation/Yeamer/Internal/Progress.hs
+++ b/Presentation/Yeamer/Internal/Progress.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2018
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
@@ -18,11 +18,13 @@
 import qualified Data.Vector as Arr
 
 import Data.ByteString (ByteString)
+import qualified Data.ByteString.Lazy as BSL
 import Data.Text (Text)
 import qualified Data.Text.Encoding as Txt
 import qualified Data.ByteString.Base64.URL as URLBase64
 
-import Data.Flat (Flat, flat, unflat)
+import Flat (Flat, flat, unflat)
+import qualified Flat.Class as Flat
 import qualified Data.Aeson as JSON
 
 import Yesod (PathPiece(..))
@@ -70,9 +72,35 @@
        (compressedProgs,progKeyRsr) = rmRedundancy $ Map.fromList keyCompressed
 
 
+-- | A hack to embed interactive values from JavaScript.
+data ValueToSet = NoValGiven
+                | ValueToSet { getValueToSet :: JSON.Value }
+    deriving (Eq,Show,Read)
+
+instance JSON.FromJSON ValueToSet where
+  parseJSON = pure . ValueToSet
+
+instance Flat ValueToSet where
+  encode (ValueToSet v) = Flat.encode $ JSON.encode v
+  encode NoValGiven = Flat.encode ()
+  decode = do
+     vj <- Flat.decode
+     case JSON.eitherDecode vj of
+       Left err -> fail err
+       Right v -> pure v
+  size (ValueToSet v) = Flat.size $ JSON.encode v
+
+data PositionChangeKind
+     = PositionAdvance
+     | PositionRevert
+     | PositionSetValue ValueToSet
+  deriving (Generic, Eq, Show, Read)
+instance JSON.FromJSON PositionChangeKind
+instance Flat PositionChangeKind
+
 data PositionChange = PositionChange
     { posChangeLevel :: PrPath
-    , posChangeIsRevert :: Bool
+    , posChangeKind :: PositionChangeKind
     } deriving (Generic, Eq, Show, Read)
 instance JSON.FromJSON PositionChange
 
@@ -84,3 +112,14 @@
                 = Txt.decodeUtf8
                  <<< URLBase64.encode
                    $ flat (lvl, isRev)
+
+
+instance PathPiece ValueToSet where
+  fromPathPiece = Txt.encodeUtf8
+                 >>> JSON.decodeStrict
+                 >>> fmap ValueToSet
+  toPathPiece NoValGiven = mempty
+  toPathPiece (ValueToSet val) = Txt.decodeUtf8
+                 <<< BSL.toStrict
+                 <<< JSON.encode
+                 $ val
diff --git a/Presentation/Yeamer/Maths.hs b/Presentation/Yeamer/Maths.hs
--- a/Presentation/Yeamer/Maths.hs
+++ b/Presentation/Yeamer/Maths.hs
@@ -3,7 +3,7 @@
 -- Copyright   : (c) Justus Sagemüller 2017
 -- License     : GPL v3
 -- 
--- Maintainer  : (@) jsagemue $ uni-koeln.de
+-- Maintainer  : (@) jsag $ hvl.no
 -- Stability   : experimental
 -- Portability : portable
 -- 
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -1,5 +1,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes       #-}
+{-# LANGUAGE DeriveGeneric     #-}
+{-# LANGUAGE TypeApplications  #-}
 
 import Presentation.Yeamer
 import Presentation.Yeamer.Maths
@@ -14,13 +16,15 @@
 import Data.Time.Clock
 import Data.Time.Clock.POSIX
 
-import Data.Flat (Flat(..))
+import Flat (Flat(..))
 
 import qualified Diagrams.Prelude as Dia
 import qualified Diagrams.Backend.Cairo as Dia
 
 import Data.Function
 
+import GHC.Generics
+
 main :: IO ()
 main = yeamer . styling ([lucius|
                   body {
@@ -45,6 +49,27 @@
                     display: flex;
                     flex-direction: column;
                   }
+                  .yeamer-display-dataEncapsulation {
+                    border: 1px solid white;
+                    border-radius: 15px;
+                    overflow: hidden;
+                    width: 90%;
+                    height: 90%;
+                  }
+                  .yeamer-display-dataConstructorName {
+                    font-weight: bold;
+                    background-color: #222;
+                  }
+                  .yeamer-display-dataConstructorName
+                     , .yeamer-display-dataFields-vert
+                     , .yeamer-display-dataFields-horiz {
+                    height: max-content;
+                  }
+                  .yeamer-display-recordFieldLabel {
+                    text-align: left;
+                    font-size: 70%;
+                    max-height: 1em;
+                  }
                  |] ()) $ do
 
 
@@ -52,6 +77,13 @@
     ======
     "Simple test “presentation”"
 
+   "Int boxes"
+    ====== do
+    (const() <$> inputBox @Int 1 →│→ \i -> fromString $ "Value is "<>show i)
+     ──
+     (const() <$> (inputBox @Double 2 →│← inputBox pi) →│→ \(i,j)
+                   -> fromString ("Sum is "<>show (i+j))
+                 )
 
    "Code block"
     ====== [plaintext|
@@ -59,8 +91,25 @@
          blub
            bli
          blum
+         <wun>
           |]
+   
+   "Lazy Haskell structures"
+    ====== do
+     "Lists"
+      ====== do
+       display [0::Int .. 16]
+        ──
+        display[ [0..n]
+               | n <- [0::Int .. ] ]
+     "Records"
+      ====== do
+       display [ RecordTest 1 Alt₀Test
+               , RecordTest 1 (Alt₁Test $ RecordTest 2 ["foo","bar"]) ]
+        ──
+        display( RecordTest 9 (Alt₁Test $ RecordTest 37 []) )
 
+
    "Some maths"
     ======
     "Let's consider "<> 𝑎*𝑏/(7-pi) $<>". This ensures"
@@ -142,3 +191,15 @@
   decode = fmap (posixSecondsToUTCTime . realToFrac . (id::Double->Double)) decode
   encode = encode . (id::Double->Double) . realToFrac . utcTimeToPOSIXSeconds
   size = size . (id::Double->Double) . realToFrac . utcTimeToPOSIXSeconds
+
+
+
+data RecordDisplayTest a = RecordTest { rtSel₀ :: !Int, rtSel₁ :: a }
+  deriving (Generic)
+
+data AlternativeDisplayTest = Alt₀Test
+                            | Alt₁Test (RecordDisplayTest [String])
+  deriving (Generic)
+
+instance InteractiveShow a => InteractiveShow (RecordDisplayTest a)
+instance InteractiveShow AlternativeDisplayTest
diff --git a/yeamer.cabal b/yeamer.cabal
--- a/yeamer.cabal
+++ b/yeamer.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                yeamer
-version:             0.1.0.5
+version:             0.1.1.0
 synopsis:            Yesod-based server for interactive presentation slides
 -- description:         
 homepage:            https://github.com/leftaroundabout/yeamer
@@ -36,20 +36,20 @@
                        , data-default-class
                        , numbered-semigroups >=0.1 && <0.2
                        , transformers
-                       , TeX-my-math >=0.201.0.0 && < 0.202
+                       , TeX-my-math >=0.201.0.0 && < 0.203
                        , dumb-cas
                        , HaTeX
-                       , texmath >=0.9 && <0.12
+                       , texmath >=0.9 && <0.13
                        , xml
                        , containers
                        , microlens >=0.4 && <0.6
                        , microlens-th
-                       , these >=0.7 && <1.1
+                       , these >=0.7 && <1.2
                        , these-lens
                        , text 
                        , bytestring 
                        , base64-bytestring 
-                       , flat >0.3.1 && <0.4
+                       , flat >0.4 && <0.5
                        , aeson 
                        , zlib
                        , filepath