add haskell solution for wk-080 ch-1

2 files changed, 34 insertions, 3 deletions

diff --git a/challenge-080/alexander-pankoff/README b/challenge-080/alexander-pankoff/README
index f1aacf3dba..a74e2fd1ec 100644
--- a/challenge-080/alexander-pankoff/README
+++ b/challenge-080/alexander-pankoff/README
@@ -1,6 +1,10 @@
 Solution by Alexander Pankoff
 
-# ch-1
+# Run the Haskell solution
 
-Aproach taken from:
-https://www.geeksforgeeks.org/count-total-set-bits-in-all-numbers-from-1-to-n/
+With a `ghc` installation you can run the haskell solution with `runghc`
+
+```
+$ runghc haskell/ch-1.hs 1 2 3 -1 4
+5
+```
diff --git a/challenge-080/alexander-pankoff/haskell/ch-1.hs b/challenge-080/alexander-pankoff/haskell/ch-1.hs
new file mode 100644
index 0000000000..d27f32fdd7
--- /dev/null
+++ b/challenge-080/alexander-pankoff/haskell/ch-1.hs
@@ -0,0 +1,27 @@
+import System.Environment (getArgs)
+import Data.List (find)
+import qualified Data.Set as Set
+
+type IntegerSet = Set.Set Integer
+
+main :: IO ()
+main = do
+  inputSet <- Set.fromList <$> (readInteger <<$>> getArgs)
+  let maybeMissing = smallestMissingPositiveNumber inputSet
+  maybe
+    (fail "no smallest missing number found.")
+    print
+    maybeMissing
+  where
+   readInteger :: String -> Integer
+   readInteger = read
+
+smallestMissingPositiveNumber :: IntegerSet -> Maybe Integer
+smallestMissingPositiveNumber set = find (not . inSet) [1..]
+ where
+  inSet = (`Set.member` set)
+
+infixl 4 <<$>>
+
+(<<$>>) :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
+(<<$>>) = fmap . fmap