Allow lines of different lengths

It thus respects the original challenge

src/Grid/Parse.hs

@@ -12,7 +12,6 @@ module Grid.Parse (toGrid) where
 import Data.Array (listArray)
 import Data.List (transpose)
 import Data.Maybe (fromJust)
-import Control.Arrow ((&&&))
 
 import Cell (Cell (Start), toCell)
 
@@ -24,13 +23,19 @@ Verify a `String` contains a valid problem.
 validateGrid :: String -> Either String String
 validateGrid s
     | null s                          = Left "Empty string"
-    | any ((/= width ls) . length) ls = Left "Rows with different lengths"
     | startCounts s == 0              = Left "No start point"
     | startCounts s > 1               = Left "More than one start point"
     | otherwise                       = Right s
-    where ls = lines s
-          width = length . head
-          startCounts = length . filter (== 'S')
+    where startCounts = length . filter (== 'S')
+
+{- |
+Limit a `String` at a specific length. If the source `String` is less than the
+targetted length, it is padded with spaces.
+-}
+limit :: Int -> String -> String
+limit i s | l >= i = take i s 
+          | otherwise = s ++ replicate (i - l) ' '
+          where l = length s
 
 {- |
 Convert a `String` into a `Grid`.
@@ -39,7 +44,7 @@ toGrid :: String -> Either String Grid
 toGrid s = validateGrid s >> return (Grid start cells)
     where
         ls = lines s
-        (width, height) = (length . head &&& length) ls
+        (width, height) = (maximum (length <$> ls), length ls)
         cells = toCell <$> listArray ((0, 0), (width - 1, height - 1))
-                                     (concat $ transpose ls)
+                                     (concat $ transpose (limit width <$> ls))
         start = fromJust $ arraySearch cells Start

test/valid01.txt

@@ -1,3 +1,3 @@
 d s<+S+--V
     |||  Q
-    -++   
+    -++

test/valid03.txt

@@ -1,4 +1,4 @@
-S-----+   
-|     +-^ 
-+---+->B  
+S-----+
+|     +-^
++---+->B
     +---^ 

test/valid04.txt

@@ -1,9 +1,9 @@
-   +---+      
-   |   |      
-   +---S---+  
-       |   |  
+   +---+
+   |   |
+   +---S---+
+       |   |
        +++++>A
        +++++>B
        +++++>C
-         |    
-         >Y   
+         |
+         >Y

test/valid05.txt

@@ -1,11 +1,11 @@
-     +-------+  +-------+--+-------+  +------+      
-     |       |  |  +-+  |  |       |  |      ++     
-     |  +----+  |  | |  |  |  +----+  |  +-+  |     
-     |  |       |  | |  |  |  |       |  | |  |     
-     |  +--+    |  +-+ ++  |  +--+    |  | |  |     
+     +-------+  +-------+--+-------+  +------+
+     |       |  |  +-+  |  |       |  |      ++
+     |  +----+  |  | |  |  |  +----+  |  +-+  |
+     |  |       |  | |  |  |  |       |  | |  |
+     |  +--+    |  +-+ ++  |  +--+    |  | |  |
 S----+     |    |   +--+   |     |    |  | |  +--->B
-     |  +--+    |  +-+ ++  |  +--+    |  | |  |     
-     |  |       |  | |  |  |  |       |  | |  |     
-     |  |       |  | |  |  |  +----+  |  +-+  |     
-     |  |       |  | |  |  |       |  |      ++     
-     +--+-------+--+ +--+  +-------+--+------+      
+     |  +--+    |  +-+ ++  |  +--+    |  | |  |
+     |  |       |  | |  |  |  |       |  | |  |
+     |  |       |  | |  |  |  +----+  |  +-+  |
+     |  |       |  | |  |  |       |  |      ++
+     +--+-------+--+ +--+  +-------+--+------+

test/valid06.txt

@@ -1,7 +1,7 @@
-  +--S--+  
+  +--S--+
 O<|  |  |>O
-  +-+++-+  
-  +-+++-+  
-  +-+++-+  
+  +-+++-+
+  +-+++-+
+  +-+++-+
 O<|  |  |>O
-  +->E<-+  
+  +->E<-+