README.md

@@ -83,4 +83,3 @@ getScoreByAge conn = do
     - [ ] `FromRow`
     - [ ] Custom `FromField` impls
 - [ ] Improve type errors when trying to `instance` a type that isn't a record (e.g. sum type)
-- [ ] Improve documentation for `fromRow` module

flake.nix

@@ -3,24 +3,33 @@
 
   outputs = { self, nixpkgs }:
     let
-      system = "x86_64-linux";
-      pkgs = nixpkgs.legacyPackages.${system};
-      opium = pkgs.haskellPackages.developPackage {
-        root = ./.;
-        modifier = drv:
-          pkgs.haskell.lib.addBuildTools drv [
-            pkgs.cabal-install
-            pkgs.haskellPackages.implicit-hie
-            pkgs.haskell-language-server
-          ];
-      };
+      pkgs = nixpkgs.legacyPackages.x86_64-linux;
     in {
-      packages.${system}.opium = pkgs.haskell.lib.overrideCabal opium {
-        # Currently the tests require a running Postgres instance.
-        # This is not automated yet, so don't export the tests.
-        doCheck = false;
+      apps.x86_64-linux.cabal = {
+        type = "app";
+        program = "${nixpkgs.legacyPackages.x86_64-linux.cabal-install}/bin/cabal";
       };
+      devShells.x86_64-linux.default = pkgs.mkShell {
+        packages = [
+          pkgs.cabal-install
+          pkgs.haskellPackages.implicit-hie
+          (pkgs.ghc.withPackages (hp: with hp; [
+            attoparsec
+            containers
+            bytestring
+            hspec
+            postgresql-libpq
+            text
+            time
+            transformers
+            vector
+          ]))
 
-      devShells.${system}.default = opium.env;
+          pkgs.haskell-language-server
+        ];
+        shellHook = ''
+          PS1="<opium> ''${PS1}"
+        '';
+      };
     };
 }

lib/Database/PostgreSQL/Opium/FromRow.hs

@@ -89,7 +89,7 @@ type family NumberOfMembers f where
   NumberOfMembers (M1 D _ f) = NumberOfMembers f
   -- The constructor has as many members as the type that it contains.
   NumberOfMembers (M1 C _ f) = NumberOfMembers f
-  -- A product type has as many members as its subtypes have together.
+  -- A product type has as many types as its subtypes have together.
   NumberOfMembers (f :*: g) = NumberOfMembers f + NumberOfMembers g
   -- A selector has/is exactly one member.
   NumberOfMembers (M1 S _ f) = 1
@@ -99,23 +99,19 @@ data FromRowCtx = FromRowCtx
   Result -- ^ Obtained from 'LibPQ.execParams'.
   ColumnTable -- ^ 'Vector' of expected columns indices and OIDs.
 
--- Specialized proxy type to be used instead of `Proxy (n, f)`
 data FRProxy (n :: Nat) (f :: Type -> Type) = FRProxy
 
 class FromRow' (n :: Nat) (f :: Type -> Type) where
   fromRow' :: FRProxy n f -> FromRowCtx -> Row -> ExceptT Error IO (f p)
 
 instance FromRow' n f => FromRow' n (M1 D c f) where
-  fromRow' FRProxy ctx row =
-    M1 <$> fromRow' @n FRProxy ctx row
+  fromRow' FRProxy ctx row = M1 <$> fromRow' @n FRProxy ctx row
 
 instance FromRow' n f => FromRow' n (M1 C c f) where
-  fromRow' FRProxy ctx row =
-    M1 <$> fromRow' @n FRProxy ctx row
+  fromRow' FRProxy ctx row = M1 <$> fromRow' @n FRProxy ctx row
 
 instance (FromRow' n f, FromRow' (n + NumberOfMembers f) g) => FromRow' n (f :*: g) where
-  fromRow' FRProxy ctx row =
-    (:*:) <$> fromRow' @n FRProxy ctx row <*> fromRow' @(n + NumberOfMembers f) FRProxy ctx row
+  fromRow' FRProxy ctx row = (:*:) <$> fromRow' @n FRProxy ctx row <*> fromRow' @(n + NumberOfMembers f) FRProxy ctx row
 
 instance {-# OVERLAPPABLE #-} (KnownNat n, KnownSymbol nameSym, FromField t) => FromRow' n (M1 S ('MetaSel ('Just nameSym) nu ns dl) (Rec0 t)) where
   fromRow' FRProxy = decodeField memberIndex nameText $ \row ->
@@ -162,3 +158,4 @@ decodeField memberIndex nameText g (FromRowCtx result columnTable) row = do
       first
         (ErrorInvalidField (ErrorPosition row nameText) oid field)
         (Just <$> fromField field)
+