From c494a25587e72104039d7045994d011ba1c2488a Mon Sep 17 00:00:00 2001
From: Jonathan Lamothe <jonathan@jlamothe.net>
Date: Sun, 30 Jun 2024 21:11:38 -0400
Subject: [PATCH] implemented `isValid` for `Word16`

---
 src/Hamming.hs             |  9 ++++++++-
 test/Hamming/Word16Spec.hs | 14 ++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/Hamming.hs b/src/Hamming.hs
index cf7d669..e660151 100644
--- a/src/Hamming.hs
+++ b/src/Hamming.hs
@@ -47,7 +47,14 @@ instance Hamming Word16 where
     , ( 0x0001, 0xfffe )
     ]
 
-  isValid = undefined
+  isValid code = not $ any (\mask -> oddParity $ code .&. mask)
+    [ 0xaaaa
+    , 0xcccc
+    , 0xf0f0
+    , 0xff00
+    , 0xffff
+    ]
+
   correctErrors = undefined
 
 setCheckBit :: (Num a, Bits a) => a -> (a, a) -> a
diff --git a/test/Hamming/Word16Spec.hs b/test/Hamming/Word16Spec.hs
index cfbffd1..f612ec5 100644
--- a/test/Hamming/Word16Spec.hs
+++ b/test/Hamming/Word16Spec.hs
@@ -47,8 +47,18 @@ setCheckBitsSpec = describe "setCheckBits" $ mapM_
   ]
 
 isValidSpec :: Spec
-isValidSpec = describe "isValid" $
-  return ()
+isValidSpec = describe "isValid" $ mapM_
+  ( \(desc, code, expected) -> context desc $ let
+    actual = isValid code
+    in it ("should be " ++ show expected) $
+      actual `shouldBe` expected
+  )
+  [ ( "all zeroes",     0,           True  )
+  , ( "all ones",       0xffff,      True  )
+  , ( "valid",          withChkBits, True  )
+  , ( "no check bits",  noChkBits,   False )
+  , ( "bad check bits", badChkBits,  False )
+  ]
 
 correctErrorsSpec :: Spec
 correctErrorsSpec = describe "correctErrors" $