From 61fd4963f106ef0df1b1673443ea164caeadf1a0 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri.lozeve@gmail.com>
Date: Thu, 1 Feb 2018 22:05:45 +0000
Subject: [PATCH] Add new instruction: draw forward without drawing a line

---
 examples/cantor.json | 27 +++++++++++++++++++++++++++
 src/Lib.hs           |  4 ++++
 2 files changed, 31 insertions(+)
 create mode 100644 examples/cantor.json

diff --git a/examples/cantor.json b/examples/cantor.json
new file mode 100644
index 0000000..ccdf4ee
--- /dev/null
+++ b/examples/cantor.json
@@ -0,0 +1,27 @@
+{
+  "name": "cantor",
+  "alphabet": "AB",
+  "axiom": "A",
+  "rules": [
+    [
+      "A",
+      "ABA"
+    ],
+    [
+      "B",
+      "BBB"
+    ]
+  ],
+  "angle": 60.0,
+  "distance": 10.0,
+  "representation": [
+    [
+      "A",
+      "Forward"
+    ],
+    [
+      "B",
+      "ForwardNoDraw"
+    ]
+  ]
+}
diff --git a/src/Lib.hs b/src/Lib.hs
index 76b8995..ebea1f0 100644
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -43,6 +43,7 @@ instance (ToJSON a) => ToJSON (LSystem a) where
 -- | Instructions for displaying the L-system
 data Instruction =
   Forward -- ^ move forward
+  | ForwardNoDraw -- ^ move forward, do not draw a line
   | TurnRight -- ^ turn right by angle
   | TurnLeft -- ^ turn left by angle
   | Push -- ^ push a position on the stack
@@ -54,6 +55,8 @@ instance FromJSON Instruction where
   parseJSON = withText "Instruction" $ \s ->
     if s `elem` ["Forward", "forward", "F", "f"] then
       pure Forward
+    else if s `elem` ["ForwardNoDraw", "forwardnodraw", "FN", "fn"] then
+      pure ForwardNoDraw
     else if s `elem` ["TurnRight", "Turnright", "turnright", "Right", "right", "R", "r"] then
       pure TurnRight
     else if s `elem` ["TurnLeft", "Turnleft", "turnleft", "Left", "left", "L", "l"] then
@@ -94,6 +97,7 @@ turtle angle distance = go 90 (Line [(0,0)]) (Pictures []) []
     go theta (Line path) (Pictures ps) stack (x:xs) =
       case x of
         Forward -> go theta (Line (p:path)) (Pictures ps) stack xs
+        ForwardNoDraw -> go theta (Line [p]) (Pictures (Line path : ps)) stack xs
         TurnRight -> go (theta + angle) (Line path) (Pictures ps) stack xs
         TurnLeft -> go (theta - angle) (Line path) (Pictures ps) stack xs
         Push -> go theta (Line path) (Pictures ps) ((head path, theta):stack) xs