From fe5e404a4b40dd0b2b34fa2d02a7fbf2c969e920 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Wed, 18 Dec 2024 23:11:52 -0800
Subject: [PATCH] comments

---
 solutions/src/2024/19.hs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/solutions/src/2024/19.hs b/solutions/src/2024/19.hs
index f90e5f4..e71f614 100644
--- a/solutions/src/2024/19.hs
+++ b/solutions/src/2024/19.hs
@@ -57,9 +57,15 @@ designWays t str = memo ! 0
 
 data Trie = Node !Bool (Map Char Trie)
 
+-- | Construct a 'Trie' that matches exactly one string.
 toTrie :: String -> Trie
 toTrie = foldr (\x t -> Node False (Map.singleton x t)) (Node True Map.empty)
 
+-- | Given a starting index find all the ending indexes for
+-- suffixes that remain after matching a string in the 'Trie'.
+--
+-- >>> matches (toTrie "pre" <> toTrie "pref") 0 "prefix"
+-- [3,4]
 matches :: Trie -> Int -> String -> [Int]
 matches (Node b xs) n yys =
   [n | b] ++