From 9765775242642200c88e966b6e175c2693358997 Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Sat, 9 Sep 2017 16:55:32 +0100
Subject: [PATCH] Define printDiff as a catamorphism.

---
 src/Renderer/SExpression.hs | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/Renderer/SExpression.hs b/src/Renderer/SExpression.hs
index c34f5b816..5d518bbc0 100644
--- a/src/Renderer/SExpression.hs
+++ b/src/Renderer/SExpression.hs
@@ -6,6 +6,7 @@ module Renderer.SExpression
 
 import Data.Bifunctor.Join
 import Data.ByteString.Char8 hiding (foldr, spanEnd)
+import Data.Functor.Foldable (cata)
 import Data.Record
 import Data.Semigroup
 import Diff
@@ -14,20 +15,20 @@ import Prelude hiding (replicate)
 import Term
 
 -- | Returns a ByteString SExpression formatted diff.
-renderSExpressionDiff :: (ConstrainAll Show fields, Foldable f) => Diff f (Record fields) -> ByteString
+renderSExpressionDiff :: (ConstrainAll Show fields, Foldable f, Functor f) => Diff f (Record fields) -> ByteString
 renderSExpressionDiff diff = printDiff diff 0 <> "\n"
 
 -- | Returns a ByteString SExpression formatted term.
-renderSExpressionTerm :: (ConstrainAll Show fields, Foldable f) => Term f (Record fields) -> ByteString
+renderSExpressionTerm :: (ConstrainAll Show fields, Foldable f, Functor f) => Term f (Record fields) -> ByteString
 renderSExpressionTerm term = printTerm term 0 <> "\n"
 
-printDiff :: (ConstrainAll Show fields, Foldable f) => Diff f (Record fields) -> Int -> ByteString
-printDiff diff level = case unDiff diff of
+printDiff :: (ConstrainAll Show fields, Foldable f, Functor f) => Diff f (Record fields) -> Int -> ByteString
+printDiff = cata $ \ diff level -> case diff of
   Patch patch -> case patch of
     Insert term -> pad (level - 1) <> "{+" <> printTerm term level <> "+}"
     Delete term -> pad (level - 1) <> "{-" <> printTerm term level <> "-}"
     Replace a b -> pad (level - 1) <> "{ " <> printTerm a level <> pad (level - 1) <> "->" <> printTerm b level <> " }"
-  Copy (Join (_, annotation)) syntax -> pad' level <> "(" <> showAnnotation annotation <> foldr (\d acc -> printDiff d (level + 1) <> acc) "" syntax <> ")"
+  Copy (Join (_, annotation)) syntax -> pad' level <> "(" <> showAnnotation annotation <> foldr (\d acc -> d (level + 1) <> acc) "" syntax <> ")"
   where
     pad' :: Int -> ByteString
     pad' n = if n < 1 then "" else pad n