From e13cc36c8a2ae63784736cfa7ad6cb0b2ac46572 Mon Sep 17 00:00:00 2001
From: totycro <totycro@unknown-horizons.org>
Date: Wed, 23 May 2012 10:43:10 +0200
Subject: Only use : instead of ++ for BufferI (constant time instead of linear
 in the worst case) delete should delete before the cursor, not after

---
 AufgabeFFP7.hs     | 17 +++++++++--------
 TestAufgabeFFP7.hs |  4 ++--
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/AufgabeFFP7.hs b/AufgabeFFP7.hs
index 099eda8..e2a7d65 100644
--- a/AufgabeFFP7.hs
+++ b/AufgabeFFP7.hs
@@ -20,11 +20,12 @@ insert c (cur, buf) = (min (length buf + 1) (max (cur + 1) 1), buf1 ++ [c] ++ bu
 -- delete character before cursor
 delete :: Buffer -> Buffer
 delete (cur, buf)
-  | buf2 == "" = (min cur (length buf1), buf1)
-  | cur < 0 = (0, buf)
-  | otherwise = (cur, buf1 ++ tail buf2)
+  | buf2 == "" = (min newCur (length buf1), buf1)
+  | newCur < 0 = (0, buf)
+  | otherwise = (newCur, buf1 ++ tail buf2)
   where
-    (buf1, buf2) = splitAt cur buf
+		newCur = cur - 1
+		(buf1, buf2) = splitAt newCur buf
 
 -- move cursor left one character
 left :: Buffer -> Buffer
@@ -52,22 +53,22 @@ emptyI = ("", "")
 
 -- insert character before cursor
 insertI :: Char -> BufferI -> BufferI
-insertI c (beforeC, afterC) = ([c] ++ beforeC, afterC)
+insertI c (beforeC, afterC) = (c:beforeC, afterC)
 
 -- delete character before cursor
 deleteI :: BufferI -> BufferI
 deleteI (beforeC, "") = (beforeC, "")
-deleteI (beforeC, c:afterC) = (beforeC, afterC)
+deleteI (c:beforeC, afterC) = (beforeC, afterC)
 
 -- move cursor left one character
 leftI :: BufferI -> BufferI
 leftI ("", afterC) = ("", afterC)
-leftI (c:beforeC, afterC) = (beforeC, [c] ++ afterC)
+leftI (c:beforeC, afterC) = (beforeC, c:afterC)
 
 -- move cursor right one character
 rightI :: BufferI -> BufferI
 rightI (beforeC, "") = (beforeC, "")
-rightI (beforeC, c:afterC) = ([c] ++ beforeC, afterC)
+rightI (beforeC, c:afterC) = (c:beforeC, afterC)
 
 -- is cursor at left end?
 atLeftI :: BufferI -> Bool
diff --git a/TestAufgabeFFP7.hs b/TestAufgabeFFP7.hs
index bbe3540..376e782 100755
--- a/TestAufgabeFFP7.hs
+++ b/TestAufgabeFFP7.hs
@@ -23,8 +23,8 @@ cases1 = TestLabel "buffer" $ TestList [
     (insert 'b' (100, "a")),
 
   TestCase $ assertEqual "delete1" (0, "bc")
-    (delete (0, "abc")),
-  TestCase $ assertEqual "delete2" (2, "ab")
+    (delete (0, "bc")),
+  TestCase $ assertEqual "delete2" (1, "ac")
     (delete (2, "abc")),
   TestCase $ assertEqual "delete3" (0, "abc")
     (delete (-100, "abc")),
-- 
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