Fractran: Difference between revisions

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 ===Generation of primes===
 Additional import
-<lang Haskell>import Data.Maybe (mapMaybe)</lang>
+<lang Haskell>import Data.Maybe (mapMaybe)
+import Data.List (elemIndex)</lang>
-<lang Haskell>primes = mapMaybe log2 $ fractran prog 2
+<lang Haskell>primes :: [Int]
+primes = mapMaybe log2 $ fractran prog 2
   where
+    prog =
-    prog = [17 % 91, 78 % 85, 19 % 51, 23 % 38, 29 % 33
-           ,77 % 29, 95 % 23, 77 % 19, 1 % 17, 11 % 13
+      [ 17 % 91
-           ,13 % 11, 15 % 14, 15 % 2, 55 % 1]
+      , 78 % 85
+      , 19 % 51
-    log2 = fmap (+ 1) . findIndex (== 2) . takeWhile even . iterate (`div` 2)</lang>
+      , 23 % 38
+      , 29 % 33
+      , 77 % 29
+      , 95 % 23
+      , 77 % 19
+      , 1 % 17
+      , 11 % 13
+      , 13 % 11
+      , 15 % 14
+      , 15 % 2
+      , 55 % 1
+      ]
+    log2 = fmap succ . elemIndex 2 . takeWhile even . iterate (`div` 2)</lang>
 <pre>λ> take 20 primes