various fixes & clarifications to exercises, thanks to Leo Varis

exercises/Set2.hs

@@ -68,6 +68,9 @@ substring i j s = todo
 -- off the front _and_ back of a string until the result is a
 -- palindrome.
 --
+-- Hint: remember the function palindrome :: String -> Bool from the
+-- course material!
+--
 -- Examples:
 --   palindromify "ab" ==> ""
 --   palindromify "aaay" ==> "aa"

exercises/Set6.hs

@@ -141,9 +141,15 @@ simplify p = todo
 -- Ex 10: implement the typeclass Num for RationalNumber. The results
 -- of addition an multiplication must be simplified.
 --
+-- Reminders:
+--   * negate x is 0-x
+--   * abs is absolute value
+--   * signum is -1, +1 or 0 depending on the sign of the input
+--
 -- Examples:
---   RationalNumber 1 2 - RationalNumber 1 3 ==> RationalNumber 1 6
+--   RationalNumber 1 3 + RationalNumber 1 6 ==> RationalNumber 1 2
 --   RationalNumber 1 3 * RationalNumber 3 1 ==> RationalNumber 1 1
+--   negate (RationalNumber 2 3)             ==> RationalNumber (-2) 3
 --   fromInteger 17 :: RationalNumber        ==> RationalNumber 17 1
 --   abs (RationalNumber (-3) 2)             ==> RationalNumber 3 2
 --   signum (RationalNumber (-3) 2)          ==> RationalNumber (-1) 1

exercises/Set7.hs

@@ -205,8 +205,8 @@ data PasswordRequirement =
   MinimumLength Int
   | ContainsSome String    -- contains at least one of given characters
   | DoesNotContain String  -- does not contain any of the given characters
-  | And PasswordRequirement PasswordRequirement -- or'ing two requirements
-  | Or PasswordRequirement PasswordRequirement    -- and'ing
+  | And PasswordRequirement PasswordRequirement -- and'ing two requirements
+  | Or PasswordRequirement PasswordRequirement  -- or'ing
   deriving Show
 
 passwordAllowed :: String -> PasswordRequirement -> Bool

exercises/Set8.hs

@@ -76,10 +76,8 @@ examplePicture1 = Picture f
 --
 -- In addition to the Picture it takes a width and a height.
 --
--- The return type is IO (), which you don't need to worry about right
--- now. A value of type IO () is something that can be executed by
--- Haskell to produce side effects (like the creation of a file in
--- this case).
+-- The return type is IO (). Check Lecture 8 for a short introduction
+-- to IO
 
 render :: Picture -> Int -> Int -> String -> IO ()
 render (Picture f) w h name = writePng name (generateImage (\x y -> colorToPixel (f (Coord x y))) w h)
@@ -92,7 +90,7 @@ render (Picture f) w h name = writePng name (generateImage (\x y -> colorToPixel
 --
 -- This should produce an example1.png file.
 --
--- Remember: You can get open GHCi with `stack ghci Set8Project.hs`
+-- Remember: You can get open GHCi with `stack ghci Set8.hs`
 
 -- For testing purposes, let's also define some functions for drawing
 -- pictures as lists. It's customary to show colours as hexadecimal
@@ -108,7 +106,6 @@ colorToHex (Color r g b) = showHex r ++ showHex g ++ showHex b
 
 getPixel :: Picture -> Int -> Int -> String
 getPixel (Picture f) x y = colorToHex (f (Coord x y))
-
 renderList :: Picture -> (Int,Int) -> (Int,Int) -> [[String]]
 renderList picture (minx,maxx) (miny,maxy) =
   [[getPixel picture x y | x <- [minx..maxx]] | y <- (reverse [miny..maxy])]
@@ -368,10 +365,10 @@ xy = Picture f
 -- The Zoom transform should scale a picture up just like the zoom function above.
 --
 -- The FlipX transform should flip the image along the vertical axis,
--- i.e. map (10,15) to (10,-15).
+-- i.e. map (10,15) to (-10,15).
 --
 -- The FlipY transform should flip the image along the horizontal
--- axis, i.e. map (10,15) to (-10,15).
+-- axis, i.e. map (10,15) to (10,-15).
 --
 -- The FlipXY transform should switch the x and y coordinates, i.e.
 -- map (10,15) to (15,10).

part1.html

@@ -2167,9 +2167,10 @@ Returns the second element of a list
 <div class="sourceCode" id="cb250"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a class="sourceLine" id="cb250-1" data-line-number="1"><span class="ot">(+) ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a <span class="ot">-&gt;</span> a</a>
 <a class="sourceLine" id="cb250-2" data-line-number="2"><span class="ot">(-) ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a <span class="ot">-&gt;</span> a</a>
 <a class="sourceLine" id="cb250-3" data-line-number="3"><span class="ot">(*) ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a <span class="ot">-&gt;</span> a</a>
-<a class="sourceLine" id="cb250-4" data-line-number="4">negate<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a</a>
-<a class="sourceLine" id="cb250-5" data-line-number="5">abs<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a</a>
-<a class="sourceLine" id="cb250-6" data-line-number="6">fromInteger<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> <span class="dt">Integer</span> <span class="ot">-&gt;</span> a</a></code></pre></div>
+<a class="sourceLine" id="cb250-4" data-line-number="4">negate<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a    <span class="co">-- 0-x</span></a>
+<a class="sourceLine" id="cb250-5" data-line-number="5">abs<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a       <span class="co">-- absolute value</span></a>
+<a class="sourceLine" id="cb250-6" data-line-number="6">signum<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> a <span class="ot">-&gt;</span> a    <span class="co">-- -1 for negative values, 0 for 0, +1 for positive values</span></a>
+<a class="sourceLine" id="cb250-7" data-line-number="7">fromInteger<span class="ot"> ::</span> <span class="dt">Num</span> a <span class="ot">=&gt;</span> <span class="dt">Integer</span> <span class="ot">-&gt;</span> a</a></code></pre></div>
 <p><code>Num</code> also shows up in the types of integer literals:</p>
 <div class="sourceCode" id="cb251"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a class="sourceLine" id="cb251-1" data-line-number="1"><span class="dt">Prelude</span><span class="fu">&gt;</span> <span class="fu">:</span>t <span class="dv">12</span></a>
 <a class="sourceLine" id="cb251-2" data-line-number="2"><span class="dv">12</span><span class="ot"> ::</span> <span class="dt">Num</span> p <span class="ot">=&gt;</span> p</a></code></pre></div>