From 83d2c07396cd3cd21462040ae34c94bf8477de6a Mon Sep 17 00:00:00 2001
From: Paul Brinkmeier <hallo@pbrinkmeier.de>
Date: Sun, 17 Sep 2023 05:31:32 +0200
Subject: [PATCH] Add FromField Word

---
 lib/Database/PostgreSQL/Opium/FromField.hs      |  5 +++++
 test/Database/PostgreSQL/Opium/FromFieldSpec.hs | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/lib/Database/PostgreSQL/Opium/FromField.hs b/lib/Database/PostgreSQL/Opium/FromField.hs
index 338e43b..2fb6302 100644
--- a/lib/Database/PostgreSQL/Opium/FromField.hs
+++ b/lib/Database/PostgreSQL/Opium/FromField.hs
@@ -56,6 +56,7 @@ instance FromField Char where
   parseField = anyChar
 
 -- | See https://www.postgresql.org/docs/current/datatype-numeric.html.
+-- We assume that 'Int' has 64 bits. This is not guaranteed but reasonable enough.
 instance FromField Int where
   validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
   parseField = signed decimal
@@ -65,6 +66,10 @@ instance FromField Integer where
   validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
   parseField = signed decimal
 
+instance FromField Word where
+  validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
+  parseField = decimal
+
 doubleParser :: Parser Double
 doubleParser = choice
   [ string "NaN" $> nan
diff --git a/test/Database/PostgreSQL/Opium/FromFieldSpec.hs b/test/Database/PostgreSQL/Opium/FromFieldSpec.hs
index 966ef55..2d3db7a 100644
--- a/test/Database/PostgreSQL/Opium/FromFieldSpec.hs
+++ b/test/Database/PostgreSQL/Opium/FromFieldSpec.hs
@@ -24,6 +24,12 @@ newtype AnInteger = AnInteger
 
 instance FromRow AnInteger where
 
+newtype AWord = AWord
+  { word :: Word
+  } deriving (Eq, Generic, Show)
+
+instance FromRow AWord where
+
 newtype AText = AText
   { text :: Text
   } deriving (Eq, Generic, Show)
@@ -90,6 +96,16 @@ spec = do
     it "Decodes bigint" $ \conn -> do
       shouldFetch conn "SELECT pow(2, 48)::BIGINT AS integer" [AnInteger $ (2 :: Integer) ^ (48 :: Integer)]
 
+  describe "FromField Word" $ do
+    it "Decodes smallint" $ \conn -> do
+      shouldFetch conn "SELECT 42::SMALLINT AS word" [AWord 42]
+
+    it "Decodes integer" $ \conn -> do
+      shouldFetch conn "SELECT pow(2, 20)::INTEGER AS word" [AWord $ (2 :: Word) ^ (20 :: Word)]
+
+    it "Decodes bigint" $ \conn -> do
+      shouldFetch conn "SELECT pow(2, 48)::BIGINT AS word" [AWord $ (2 :: Word) ^ (48 :: Word)]
+
   describe "FromField Text" $ do
     it "Decodes text" $ \conn -> do
       shouldFetch conn "SELECT 'Hello, World!'::TEXT AS text" [AText "Hello, World!"]