From 220bc3db07745f9e718720d7a2590aeabc175d9b Mon Sep 17 00:00:00 2001
From: wes <wjak56@gmail.com>
Date: Sun, 2 Jul 2017 23:59:57 -0400
Subject: [PATCH] suffix trees in haskell

---
 suffixes.hs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 suffixes.hs

diff --git a/suffixes.hs b/suffixes.hs
new file mode 100644
index 0000000..42386dc
--- /dev/null
+++ b/suffixes.hs
@@ -0,0 +1,28 @@
+#! /usr/bin/env runghc
+
+import qualified Data.List as L
+import qualified Data.Function as F
+import Control.Monad
+
+data Trie = TBranch {
+              getRoot :: String,
+              getChildren :: [Trie]
+            }
+  deriving (Show)
+
+notEmpty [] = False
+notEmpty _ = True
+
+buildTrie [] = TBranch "" []
+buildTrie words =
+  let root   = head $ head words
+      groups = groupTails $ map tail words
+        in TBranch [root] $ map buildTrie groups
+
+trie words = TBranch "" (map buildTrie $ groupTails $ tails words)
+
+groupTails [] = []
+groupTails xs = L.groupBy ((==) `F.on` head) $ L.sort $ filter notEmpty xs
+
+tails "" = []
+tails (w@(c:cs)) =  w : tails cs