diff --git a/src/Operation.hs b/src/Operation.hs
index 57b8fde59..bccbbb8bf 100644
--- a/src/Operation.hs
+++ b/src/Operation.hs
@@ -5,8 +5,16 @@ import Data.OrderedMap
 import qualified Data.Text as T
 import Term
 
-data Operation a annotation f
-  = Recursive (Term a annotation) (Term a annotation) (Diff a annotation -> f)
+-- | A single step in a diffing algorithm.
+data Operation
+  a -- ^ The type of leaves in the syntax tree, typically String, but possibly some datatype representing different leaves more precisely.
+  annotation -- ^ The type of annotations.
+  f -- ^ The type representing another level of the diffing algorithm. Often Algorithm.
+  =
+  -- | Recursively diff two terms and pass the result to the continuation.
+  Recursive (Term a annotation) (Term a annotation) (Diff a annotation -> f)
+  -- | Diff two dictionaries and pass the result to the continuation.
   | ByKey (OrderedMap T.Text (Term a annotation)) (OrderedMap T.Text (Term a annotation)) (OrderedMap T.Text (Diff a annotation) -> f)
+  -- | Diff two arrays and pass the result to the continuation.
   | ByIndex [Term a annotation] [Term a annotation] ([Diff a annotation] -> f)
   deriving Functor