From 93578c7ddcd6f9dac0518e2b53450a721457bf14 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri.lozeve@gmail.com>
Date: Tue, 16 Jan 2018 10:24:13 +0000
Subject: [PATCH] Add Haddock documentation

---
 app/Examples.hs | 19 ++++++++++++++++++-
 src/Lib.hs      | 40 ++++++++++++++++++++++++++++++----------
 2 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/app/Examples.hs b/app/Examples.hs
index 00bbbe8..8472cec 100644
--- a/app/Examples.hs
+++ b/app/Examples.hs
@@ -1,13 +1,17 @@
 module Examples
-  ( gosper
+  ( -- * Space-filling curves
+    gosper
   , hilbert
+    -- * Fractals
   , koch
+  , kochSnowflake
   , sierpinski
   , sierpinskiArrow
   ) where
 
 import Lib
 
+-- | Gosper curve
 gosper :: LSystem Char
 gosper = LSystem
          "AB+-"
@@ -18,6 +22,7 @@ gosper = LSystem
          10
          [('A',Forward), ('B',Forward), ('+',TurnRight), ('-',TurnLeft)]
 
+-- | Hilbert curve
 hilbert = LSystem
           "ABF+-"
           "A"
@@ -27,6 +32,7 @@ hilbert = LSystem
           10
           [('F',Forward), ('+',TurnRight), ('-',TurnLeft)]
 
+-- | Koch curve
 koch = LSystem
        "F+-"
        "F"
@@ -35,6 +41,16 @@ koch = LSystem
        10
        [('F',Forward), ('+',TurnRight), ('-',TurnLeft)]
 
+-- | Koch snowflake
+kochSnowflake = LSystem
+                "F+-"
+                "F"
+                [('F', "F+F--F+F")]
+                60
+                10
+                [('F',Forward), ('+',TurnRight), ('-',TurnLeft)]
+
+-- | Sierpinski triangle
 sierpinski = LSystem
              "AB+-"
              "A-B-B"
@@ -44,6 +60,7 @@ sierpinski = LSystem
              10
              [('A',Forward), ('B',Forward), ('+',TurnRight), ('-',TurnLeft)]
 
+-- | Sierpinski arrowhead curve
 sierpinskiArrow = LSystem
                   "AB+-"
                   "A"
diff --git a/src/Lib.hs b/src/Lib.hs
index 0522027..993da56 100644
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -1,6 +1,8 @@
 module Lib
-    ( LSystem(..)
+    ( -- * L-system data types
+      LSystem(..)
     , Instruction(..)
+      -- * L-system functions
     , iterateLSystem
     , instructions
     , drawLSystem
@@ -9,20 +11,32 @@ module Lib
 import Data.Maybe
 import Graphics.Gloss
 
+-- | L-system data type
 data LSystem a = LSystem
-  { alphabet :: [a]
-  , axiom :: [a]
-  , rules :: [(a, [a])]
-  , angle :: Float
-  , distance :: Float
-  , representation :: [(a, Instruction)]
+  { alphabet :: [a] -- ^ variables and constants used by the system
+  , axiom :: [a] -- ^ initial state of the system
+  , rules :: [(a, [a])] -- ^ production rules defining how each
+                        -- variable can be replaced by a sequence of
+                        -- variables and constants
+  , angle :: Float -- ^ angle used for the representation
+  , distance :: Float -- ^ distance of each segment in the representation
+  , representation :: [(a, Instruction)] -- ^ representation rules
+                                         -- defining how each variable
+                                         -- and constant should be
+                                         -- represented
   } deriving (Eq, Show)
 
-data Instruction = Forward | TurnRight | TurnLeft | Stay
+-- | Instructions for displaying the L-system
+data Instruction =
+  Forward -- ^ move forward
+  | TurnRight -- ^ turn right by angle
+  | TurnLeft -- ^ turn left by angle
+  | Stay -- ^ do nothing
   deriving (Eq, Show)
 
 
-iterateLSystem :: (Eq a, Num t, Eq t) => t -> LSystem a -> LSystem a
+-- | Iterate the L-system by n steps
+iterateLSystem :: (Eq a, Integral t) => t -> LSystem a -> LSystem a
 iterateLSystem 0 lsystem = lsystem
 iterateLSystem n (LSystem a ax r ang dist rep) =
   iterateLSystem (n-1) $ LSystem a ax' r ang dist rep
@@ -31,11 +45,16 @@ iterateLSystem n (LSystem a ax r ang dist rep) =
                 Just xs -> xs
                 Nothing -> [x]
 
+-- | Generate a set of instructions from an L-system
 instructions :: Eq a => LSystem a -> [Instruction]
 instructions (LSystem a ax r ang dist rep) = mapMaybe f ax
   where f x = lookup x rep
 
-turtle :: Float -> Float -> [Instruction] -> Picture
+-- | Draw a sequence of instructions
+turtle :: Float -- ^ angle
+  -> Float -- ^ distance
+  -> [Instruction] -- ^ sequence of instruction
+  -> Picture -- ^ generated picture
 turtle angle distance = go 0 (Line [(0,0)])
   where go _ ps [] = ps
         go theta (Line path) (x:xs) =
@@ -49,6 +68,7 @@ turtle angle distance = go 0 (Line [(0,0)])
             thetaRad = theta * pi / 180
             p = (px + distance * cos thetaRad, py + distance * sin thetaRad)
 
+-- | Draw an L-system
 drawLSystem :: Eq a => LSystem a -> Picture
 drawLSystem ls@(LSystem a ax r ang dist rep) = turtle ang dist $ instructions ls