print begin

src/Gyehoek/Sexp/Syntax.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE ApplicativeDo #-}
 module Gyehoek.Sexp.Syntax
   ( DatumF(..)
   , Simple(..)
@@ -22,7 +23,10 @@ module Gyehoek.Sexp.Syntax
   , pattern Vector
   , pattern DotList
   , pattern Gyehoek.Sexp.Syntax.List
+  , syntax
+  , indentation
   , adorn
+  , indentWith
   , pattern Bytevector
   , pattern Symbol
   , pattern String
@@ -36,7 +40,7 @@ import Data.Scientific (Scientific)
 import Data.ByteString (ByteString)
 import Gyehoek.Prelude hiding ((:<), Simple)
 import Text.Megaparsec.Pos (SourcePos(..))
-import Control.Comonad.Cofree (Cofree((:<)))
+import Control.Comonad.Cofree (Cofree((:<)), _extract)
 import Data.Fix (Fix (..))
 import Data.Functor.Foldable
 import Text.Show.Deriving (deriveShow1)
@@ -112,9 +116,21 @@ data Syn
 deriveShow1 ''CompoundF
 deriveShow1 ''DatumF
 
+syntax :: Lens' Datum Syn
+syntax = _extract
+
+indentation :: Traversal' Datum Indentation
+indentation k (syn :< CompoundF (ListF ind xs)) = do
+  ind' <- k ind
+  pure $ syn :< CompoundF (ListF ind' xs)
+indentation k a = pure a
+
 adorn :: Syn -> Datum -> Datum
 adorn syn (_ :< d) = syn :< d
 
+indentWith :: Indentation -> Datum -> Datum
+indentWith = set indentation
+
 pattern Simple :: Simple -> Datum
 pattern Simple a <- _ :< SimpleF a
   where Simple a = SynNone :< SimpleF a