add div by zero protection + some indentions fixes

1 files changed, 40 insertions, 20 deletions

diff --git a/AufgabeFFP6.hs b/AufgabeFFP6.hs
index c60053d..1f2faff 100644
--- a/AufgabeFFP6.hs
+++ b/AufgabeFFP6.hs
@@ -4,6 +4,7 @@ module AufgabeFFP6
 where
 
 import Data.Array
+import Debug.Trace
 
 type F  = Array Int Int
 type Op = Int -> Int -> Int
@@ -33,11 +34,30 @@ yield = yield_bt
 
 --------------------------------------------------------------------------------
 
+instance Eq (Integer -> Integer -> Integer) where
+  (==) op1 op2 = ((op1 3 3) - (op2 3 3)) == 0
+instance Eq (Int -> Int -> Int) where
+  (==) op1 op2 = ((op1 3 3) - (op2 3 3)) == 0
+
+check_divByZero :: F -> G -> Bool
+check_divByZero f g = check_divByZero' (tail (elems f)) (elems g)
+  where
+    check_divByZero' _ [] = True
+    check_divByZero' [] _ = True
+    check_divByZero' (f:fs) (g:gs)
+      | f == 0 && g == (./.) = False
+      | otherwise = True && check_divByZero' fs gs
+
+--------------------------------------------------------------------------------
+
 type Node = ([Int], [Int], W, [Op])
 
 goal_yield_bt :: Node -> Bool
 goal_yield_bt (_, _, _, []) = False -- no operators
-goal_yield_bt (f, [], w, g) = eval (listArray (1, length f) f) (listArray (1, length g) g) == w
+goal_yield_bt (f, [], w, g) = check_divByZero f' g' && eval f' g' == w
+  where
+    f' = listArray (1, length f) f
+    g' = listArray (1, length g) g
 goal_yield_bt (_, _, _, _) = False
 
 succ_yield_bt :: Node -> [Node]
@@ -93,31 +113,31 @@ yield_gtf = filt . transform . generate
 
 -- produce [G] by using get_combinations
 generate :: F -> W -> (F, W, [G])
-generate f w =  (f, w, [ array (1,n) entries | entries <- get_combinations n ] )
-        where 
-        n = (snd $ bounds f) - 1
+generate f w =  (f, w, [ array (1,n) entries | entries <- get_combinations n ])
+  where
+    n = (snd $ bounds f) - 1
 
--- provide all selections of length n, work recursively and attach index for level (convenient for creating arrays)
+-- provide all selections of length n, work recursively and attach index for
+-- level (convenient for creating arrays)
 get_combinations :: Int -> [[(Int, Op)]]
-get_combinations 1 = [[(1,(+))], [(1, (-))], [(1, (*))], [(1,(./.))]]
+get_combinations 1 = [[(1,(+))], [(1,(-))], [(1,(*))], [(1,(./.))]]
 get_combinations n = [ (up i) ++ entr  | entr <- get_combinations (n-1), i <- get_combinations 1 ]
-        where 
-        up = map (\(num, x) -> ((num+n-1), x))
+  where
+    up = map (\(num, x) -> ((num + n - 1), x))
 
--- attaches a list of results 
-transform ::  (W -> (F,W,[G])) -> W -> ((F, W, [G]), [W])
-transform fun w = ((f, w, g), map (eval f) g )
-        where 
-        (f, w, g) = fun w
+-- attaches a list of results
+transform ::  (W -> (F, W, [G])) -> W -> ((F, W, [G]), [W])
+transform fun w = ((f, w, g'), map (eval f) g')
+  where
+    (f, w, g) = fun w
+    g' = filter (\g'' -> check_divByZero f g'') g
 
--- take those, where the entry in the result list corresponds to 
-filt :: (W -> ((F,W,[G]),[W]) ) -> W -> [G]
+-- take those, where the entry in the result list corresponds to
+filt :: (W -> ((F, W, [G]), [W]) ) -> W -> [G]
 filt fun w = [ g!!i | i <- [0..n], res!!i == w ]
-        where
-        ( (f, _, g), res ) = fun w
-        n = (length g) - 1
-
-
+  where
+    ( (f, _, g), res ) = fun w
+    n = (length g) - 1
 
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