dynamic.hs

dynamic.hs

@@ -0,0 +1,25 @@
+import Data.Dynamic
+import Data.Foldable
+
+mixedList =
+    [ toDyn True
+    , toDyn (5 :: Integer)
+    , toDyn "hey"
+    ]
+
+main =
+    for_ mixedList $ \d ->
+        putStrLn (message d)
+
+recognizeType d =
+  asum
+    [ (fromDynamic d :: Maybe Integer) >>= \x ->
+        Just (show x ++ " is an integer")
+    , (fromDynamic d :: Maybe Bool) >>= \x ->
+        Just ("The answer is " ++ (if x then "yes" else "no"))
+    ]
+
+message d =
+    case (recognizeType d) of
+        Just x -> x
+        Nothing -> "Unrecognized type: " ++ show (dynTypeRep d)

outputs/dynamic.txt

@@ -0,0 +1,3 @@
+The answer is yes
+5 is an integer
+Unrecognized type: [Char]

tools/outputs.nix

@@ -24,6 +24,7 @@ in
     (run' "branching.txt" ../branching.hs { sed = ["s!^It's .* noon$!It's ... noon!"]; })
     (run "common-types.txt" ../common-types.hs)
     (run "crypto-hashing.txt" ../crypto-hashing.hs)
+    (run "dynamic.txt" ../dynamic.hs)
     (run "for-loops.txt" ../for-loops.hs)
     (run "hashing.txt" ../hashing.hs)
     (run "hello-world.txt" ../hello-world.hs)