From e3e3dc1ffd5dc8111dd348a945ce3be73217ae0b Mon Sep 17 00:00:00 2001
From: Tony Morris <tmorris@tmorris.net>
Date: Tue, 10 Sep 2013 15:57:53 +1000
Subject: [PATCH] fix tests

---
 src/Core.hs           |  2 --
 src/Monad/Monad.hs    |  6 +++---
 src/Structure/List.hs | 16 ++++++++++++++++
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/src/Core.hs b/src/Core.hs
index 569954c2c..a0d9ef785 100644
--- a/src/Core.hs
+++ b/src/Core.hs
@@ -39,7 +39,6 @@ module Core(
   , getChar
   , concatMap
   , length
-  , product
   , replicate
   , foldr
   , (++)
@@ -86,7 +85,6 @@ import Prelude(
   , getChar
   , concatMap
   , length
-  , product
   , replicate
   , foldr
   , (++)
diff --git a/src/Monad/Monad.hs b/src/Monad/Monad.hs
index 05b6fa48b..4a854a9ab 100644
--- a/src/Monad/Monad.hs
+++ b/src/Monad/Monad.hs
@@ -187,7 +187,7 @@ apply =
 -- >>> lift2 (+) Empty (Full 8)
 -- Empty
 --
--- >>> lift2 (+) length sum [4,5,6]
+-- >>> lift2 (+) len sum (listh [4,5,6])
 -- 18
 lift2 ::
   Monad m =>
@@ -222,7 +222,7 @@ lift2 =
 -- >>> lift3 (\a b c -> a + b + c) Empty Empty (Full 9)
 -- Empty
 --
--- >>> lift3 (\a b c -> a + b + c) length sum product [4,5,6]
+-- >>> lift3 (\a b c -> a + b + c) len sum product (listh [4,5,6])
 -- 138
 lift3 ::
   Monad m =>
@@ -258,7 +258,7 @@ lift3 =
 -- >>> lift4 (\a b c d -> a + b + c + d) Empty Empty (Full 9) (Full 10)
 -- Empty
 --
--- >>> lift4 (\a b c d -> a + b + c + d) length sum product (sum . filter even) [4,5,6]
+-- >>> lift4 (\a b c d -> a + b + c + d) len sum product (sum . filter even) (listh [4,5,6])
 -- 148
 lift4 ::
   Monad m =>
diff --git a/src/Structure/List.hs b/src/Structure/List.hs
index d735c2e51..9dd8567f1 100644
--- a/src/Structure/List.hs
+++ b/src/Structure/List.hs
@@ -67,6 +67,19 @@ headOr ::
 headOr =
   error "todo"
 
+-- | The product of the elements of a list.
+--
+-- >>> product (1 :. 2 :. 3 :. Nil)
+-- 6
+--
+-- >>> product (1 :. 2 :. 3 :. 4 :. Nil)
+-- 24
+product ::
+  List Int
+  -> Int
+product =
+  foldLeft (*) 1
+
 -- Exercise 2
 -- Relative Difficulty: 2
 -- Correctness:   2.5 marks
@@ -79,6 +92,9 @@ headOr =
 -- >>> sum (1 :. 2 :. 3 :. Nil)
 -- 6
 --
+-- >>> sum (1 :. 2 :. 3 :. 4 :. Nil)
+-- 10
+--
 -- prop> foldLeft (-) (sum x) x == 0
 sum ::
   List Int