Review ch2 exercise solutions

Author: dwayne

ch2/01-comprehension-check.txt

@@ -0,0 +1,37 @@
+Exercises: Comprehension Check
+
+1.
+
+Given,
+
+half x = x / 2
+square x = x * x
+
+Then, in the REPL we write them as
+
+> half x = x / 2
+> square x = x * x
+
+> half 5
+2.5
+> half 4
+2
+> :t half
+half :: Fractional a => a -> a
+
+> square 4
+16
+> :t square
+square :: Num a => a -> a
+
+2.
+
+areaOfCircle r = 3.14 * (r * r)
+-- or
+-- areaOfCircle r = 3.14 * square r
+
+3.
+
+areaOfCircle r = pi * (r * r)
+-- or
+-- areaOfCircle r = pi * square r

ch2/ex2.txt renamed to ch2/02-parentheses-and-association.txt

@@ -0,0 +1,14 @@
+Exercises: Heal the Sick
+
+1. area x = 3.14 * (x * x) -- extra space 3._14
+
+2. double x = x * 2 -- variable b not in scope
+
+-- or
+-- double b = b * 2
+
+3.
+
+x = 7
+y = 10 -- incorrect indentation
+f = x + y

ch2/03-heal-the-sick.txt

@@ -0,0 +1,21 @@
+Exercises: A Head Code
+
+1.
+
+> let x = 5 in x
+5
+
+2.
+
+> let x = 5 in x * x
+25
+
+3.
+
+> let x = 5; y = 6 in x * y
+30
+
+4.
+
+> let x = 3; y = 1000 in x + 3
+6

ch2/ex5.hs renamed to ch2/04-a-head-code.hs

@@ -29,21 +29,25 @@ Equivalent expressions
 
 More fun with functions
 
-let z = 7         ; z = 7
-let y = z + 8     ; y = 15
-let x = y ^ 2     ; x = 225
-let waxOn = x * 5 ; waxOn = 1125
+> z = 7         ; z = 7
+> y = z + 8     ; y = 15
+> x = y ^ 2     ; x = 225
+> waxOn = x * 5 ; waxOn = 1125
 
 1. 10 + waxOn = 1135
    (+10) waxOn = 1135
    (-) 15 waxOn = 15 - waxOn = -1110
    (-) waxOn 15 = waxOn - 15 = 1110
 
-2. let triple x = x * 3
+2.
 
-3. triple waxOn = triple 1125
-                = 1125 * 3
-                = 3375
+> triple x = x * 3
+
+3.
+
+triple waxOn = triple 1125
+             = 1125 * 3
+             = 3375
 
 4. See waxOn.hs
 

ch2/04-a-head-code.txt

@@ -1,4 +1,10 @@
-There is a difference between `div`/`mod` and `quot`/`rem`. Be careful when
-choosing between these functions.
+Notes:
 
-See http://stackoverflow.com/a/28027235/391924.
+- [Using GHCi](https://downloads.haskell.org/ghc/8.6.5/docs/html/users_guide/ghci.html)
+- There is a difference between `div`/`mod` and `quot`/`rem`. Be careful when choosing between these functions. See http://stackoverflow.com/a/28027235/391924.
+- Haskell doesn't evaluate everything to canonical or normal form by default. Instead, it only evaluates to weak head normal form (WHNF) by default.
+
+Follow-up resources:
+
+- [Let vs Where](https://wiki.haskell.org/Let_vs._Where)
+- [How to desugar Haskell code](https://www.haskellforall.com/2014/10/how-to-desugar-haskell-code.html)