implemented overlay

src/Mtlstats/Format.hs

@@ -24,6 +24,7 @@ module Mtlstats.Format
   , left
   , right
   , centre
+  , overlay
   , month
   ) where
 
@@ -74,6 +75,17 @@ centre n str = let
   pad  = replicate pLen ' '
   in take n $ pad ++ str ++ repeat ' '
 
+-- | Overlays one string on top of another
+overlay
+  :: String
+  -- ^ The string on the top
+  -> String
+  -- ^ The string on the bottom
+  -> String
+overlay (x:xs) (_:ys) = x : overlay xs ys
+overlay xs []         = xs
+overlay [] ys         = ys
+
 -- | Converts a number to a three character month (e.g. @"JAN"@)
 month :: Int -> String
 month 1  = "JAN"

test/FormatSpec.hs

@@ -31,6 +31,7 @@ spec = describe "Mtlstats.Format" $ do
   leftSpec
   rightSpec
   centreSpec
+  overlaySpec
   monthSpec
 
 padNumSpec :: Spec
@@ -89,6 +90,17 @@ centreSpec = describe "centre" $ do
     it "should truncate the text" $
       centre 2 "foo" `shouldBe` "fo"
 
+overlaySpec :: Spec
+overlaySpec = describe "overlay" $ do
+
+  context "first string shorter" $
+    it "should overlay" $
+      overlay "foo" "abc123" `shouldBe` "foo123"
+
+  context "first string longer" $
+    it "should overlay" $
+      overlay "abc123" "foo" `shouldBe` "abc123"
+
 monthSpec :: Spec
 monthSpec = describe "month" $ do