From 0cb0a5e239d3ea65b579d68d17f1de9f624c7ab6 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 3 Feb 2023 09:39:44 -0800
Subject: [PATCH 1/2] Commonmark.Html: export transform.

This is a function that allows you to walk the tree
of HTML nodes, applying a transformation.
---
 commonmark/src/Commonmark/Html.hs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/commonmark/src/Commonmark/Html.hs b/commonmark/src/Commonmark/Html.hs
index 6226eb2..7c82ac5 100644
--- a/commonmark/src/Commonmark/Html.hs
+++ b/commonmark/src/Commonmark/Html.hs
@@ -13,6 +13,7 @@ module Commonmark.Html
   , renderHtml
   , escapeURI
   , escapeHtml
+  , transform
   )
 where
 
@@ -463,3 +464,8 @@ escapeURIChar c
                                      '#','!','$','\'','(',')','*','+',',',
                                      ';','=']
 
+-- | Walk HTML nodes bottom-up, applying a function.
+transform :: (Html a -> Html a) -> Html a -> Html a
+transform f (HtmlElement et name attr (Just elt)) =
+  f $ HtmlElement et name attr (Just (transform f elt))
+transform f elt = f elt

From ef35cd4b905149bd21f7f54d7d6d9c03e4553971 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Sat, 4 Feb 2023 10:32:08 -0800
Subject: [PATCH 2/2] Commonmark.Html: export Html constructors and transformM.

API change:

- Export constructors for Html.
- Export ElementType
- Re-export Attribute
- Export transformM, a monadic version of transform.
---
 commonmark/src/Commonmark/Html.hs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/commonmark/src/Commonmark/Html.hs b/commonmark/src/Commonmark/Html.hs
index 7c82ac5..dee7e1a 100644
--- a/commonmark/src/Commonmark/Html.hs
+++ b/commonmark/src/Commonmark/Html.hs
@@ -4,7 +4,9 @@
 {-# LANGUAGE FlexibleContexts           #-}
 {-# LANGUAGE UndecidableInstances       #-}
 module Commonmark.Html
-  ( Html
+  ( Html(..)
+  , ElementType(..)
+  , Attribute
   , htmlInline
   , htmlBlock
   , htmlText
@@ -14,6 +16,7 @@ module Commonmark.Html
   , escapeURI
   , escapeHtml
   , transform
+  , transformM
   )
 where
 
@@ -469,3 +472,10 @@ transform :: (Html a -> Html a) -> Html a -> Html a
 transform f (HtmlElement et name attr (Just elt)) =
   f $ HtmlElement et name attr (Just (transform f elt))
 transform f elt = f elt
+
+-- | Walk HTML nodes bottom-up, applying a function, in a monadic context.
+transformM :: Monad m => (Html a -> m (Html a)) -> Html a -> m (Html a)
+transformM f (HtmlElement et name attr (Just elt)) = do
+  elt' <- transformM f elt
+  f $ HtmlElement et name attr (Just elt')
+transformM f elt = f elt