Minor fixes

README.md

@@ -83,3 +83,4 @@ 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

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 types as its subtypes have together.
+  -- A product type has as many members as its subtypes have together.
   NumberOfMembers (f :*: g) = NumberOfMembers f + NumberOfMembers g
   -- A selector has/is exactly one member.
   NumberOfMembers (M1 S _ f) = 1
@@ -99,19 +99,23 @@ 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 ->
@@ -158,4 +162,3 @@ decodeField memberIndex nameText g (FromRowCtx result columnTable) row = do
       first
         (ErrorInvalidField (ErrorPosition row nameText) oid field)
         (Just <$> fromField field)
-