diff --git a/squeal-postgresql/squeal-postgresql.cabal b/squeal-postgresql/squeal-postgresql.cabal
index bf37cee..1794c50 100644
--- a/squeal-postgresql/squeal-postgresql.cabal
+++ b/squeal-postgresql/squeal-postgresql.cabal
@@ -28,7 +28,6 @@ library
     Squeal.PostgreSQL.Definition.Function
     Squeal.PostgreSQL.Definition.Index
     Squeal.PostgreSQL.Definition.Table
-    Squeal.PostgreSQL.Definition.Table.Column
     Squeal.PostgreSQL.Definition.Table.Constraint
     Squeal.PostgreSQL.Definition.Type
     Squeal.PostgreSQL.Definition.Schema
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL.hs b/squeal-postgresql/src/Squeal/PostgreSQL.hs
index f2226d8..5324ffd 100644
--- a/squeal-postgresql/src/Squeal/PostgreSQL.hs
+++ b/squeal-postgresql/src/Squeal/PostgreSQL.hs
@@ -199,7 +199,6 @@ import Squeal.PostgreSQL.Definition.Function as X
 import Squeal.PostgreSQL.Definition.Index as X
 import Squeal.PostgreSQL.Definition.Schema as X
 import Squeal.PostgreSQL.Definition.Table as X
-import Squeal.PostgreSQL.Definition.Table.Column as X
 import Squeal.PostgreSQL.Definition.Table.Constraint as X
 import Squeal.PostgreSQL.Definition.Type as X
 import Squeal.PostgreSQL.Definition.View as X
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL/Definition.hs b/squeal-postgresql/src/Squeal/PostgreSQL/Definition.hs
index 5da283a..fc14768 100644
--- a/squeal-postgresql/src/Squeal/PostgreSQL/Definition.hs
+++ b/squeal-postgresql/src/Squeal/PostgreSQL/Definition.hs
@@ -35,8 +35,6 @@ module Squeal.PostgreSQL.Definition
     Definition (..)
   , (>>>)
   , manipDefinition
-  , PGNullityTyped (..)
-  , hask
   ) where
 
 import Control.Category
@@ -47,10 +45,7 @@ import Prelude hiding ((.), id)
 
 import qualified GHC.Generics as GHC
 
-import Squeal.PostgreSQL.Definition.Table.Column
-import Squeal.PostgreSQL.Expression.Type
 import Squeal.PostgreSQL.Manipulation
-import Squeal.PostgreSQL.PG
 import Squeal.PostgreSQL.Render
 import Squeal.PostgreSQL.Schema
 
@@ -85,24 +80,3 @@ manipDefinition
   -- ^ no input or output
   -> Definition schemas schemas
 manipDefinition = UnsafeDefinition . (<> ";") . renderSQL
-
--- | Like @PGTyped@ but also accounts for nullity.
-class PGNullityTyped schemas (nullty :: NullityType) where
-  pgNullityType :: ColumnTypeExpression schemas ('NoDef :=> nullty)
-
-instance PGTyped schemas ('Null ty) => PGNullityTyped schemas ('Null ty) where
-  pgNullityType = nullable (pgtype @_ @('Null ty))
-
-instance PGTyped schemas ('NotNull ty) => PGNullityTyped schemas ('NotNull ty) where
-  pgNullityType = notNullable (pgtype @_ @('NotNull ty))
-
--- | Allow you to specify pg column types in relation to haskell types.
--- >>> printSQL $ hask @(Maybe String)
--- text NULL
---
--- >>> printSQL $ hask @Double
--- float8 NOT NULL
-hask
-  :: forall h schemas. PGNullityTyped schemas (NullPG h)
-  => ColumnTypeExpression schemas ('NoDef :=> NullPG h)
-hask = pgNullityType
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table.hs b/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table.hs
index b01e300..57d0c12 100644
--- a/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table.hs
+++ b/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table.hs
@@ -62,9 +62,9 @@ import qualified GHC.Generics as GHC
 
 import Squeal.PostgreSQL.Alias
 import Squeal.PostgreSQL.Definition
-import Squeal.PostgreSQL.Definition.Table.Column
 import Squeal.PostgreSQL.Definition.Table.Constraint
 import Squeal.PostgreSQL.Expression
+import Squeal.PostgreSQL.Expression.Type
 import Squeal.PostgreSQL.List
 import Squeal.PostgreSQL.Render
 import Squeal.PostgreSQL.Schema
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table/Column.hs b/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table/Column.hs
deleted file mode 100644
index d2fd2d4..0000000
--- a/squeal-postgresql/src/Squeal/PostgreSQL/Definition/Table/Column.hs
+++ /dev/null
@@ -1,105 +0,0 @@
-{-|
-Module: Squeal.PostgreSQL.Definition.Table.Column
-Description: Column type expressions
-Copyright: (c) Eitan Chatav, 2017
-Maintainer: eitan@morphism.tech
-Stability: experimental
-
-Column type expressions.
--}
-
-{-# LANGUAGE
-    AllowAmbiguousTypes
-  , ConstraintKinds
-  , DeriveAnyClass
-  , DeriveGeneric
-  , DerivingStrategies
-  , FlexibleContexts
-  , FlexibleInstances
-  , GADTs
-  , LambdaCase
-  , MultiParamTypeClasses
-  , OverloadedLabels
-  , OverloadedStrings
-  , RankNTypes
-  , ScopedTypeVariables
-  , TypeApplications
-  , TypeInType
-  , TypeOperators
-  , UndecidableSuperClasses
-#-}
-
-module Squeal.PostgreSQL.Definition.Table.Column
-  ( ColumnTypeExpression (..)
-  , nullable
-  , notNullable
-  , default_
-  , serial2
-  , smallserial
-  , serial4
-  , serial
-  , serial8
-  , bigserial
-  ) where
-
-import Control.DeepSeq
-import Data.ByteString
-
-import qualified GHC.Generics as GHC
-
-import Squeal.PostgreSQL.Alias
-import Squeal.PostgreSQL.Expression
-import Squeal.PostgreSQL.Expression.Type
-import Squeal.PostgreSQL.Render
-import Squeal.PostgreSQL.Schema
-
--- $setup
--- >>> import Squeal.PostgreSQL
-
--- | `ColumnTypeExpression`s are used in `createTable` commands.
-newtype ColumnTypeExpression (schemas :: SchemasType) (ty :: ColumnType)
-  = UnsafeColumnTypeExpression { renderColumnTypeExpression :: ByteString }
-  deriving (GHC.Generic,Show,Eq,Ord,NFData)
-instance RenderSQL (ColumnTypeExpression schemas ty) where
-  renderSQL = renderColumnTypeExpression
-
--- | used in `createTable` commands as a column constraint to note that
--- @NULL@ may be present in a column
-nullable
-  :: TypeExpression schemas (nullity ty)
-  -> ColumnTypeExpression schemas ('NoDef :=> 'Null ty)
-nullable ty = UnsafeColumnTypeExpression $ renderSQL ty <+> "NULL"
-
--- | used in `createTable` commands as a column constraint to ensure
--- @NULL@ is not present in a column
-notNullable
-  :: TypeExpression schemas (nullity ty)
-  -> ColumnTypeExpression schemas ('NoDef :=> 'NotNull ty)
-notNullable ty = UnsafeColumnTypeExpression $ renderSQL ty <+> "NOT NULL"
-
--- | used in `createTable` commands as a column constraint to give a default
-default_
-  :: Expression '[] '[] 'Ungrouped schemas '[] '[] ty
-  -> ColumnTypeExpression schemas ('NoDef :=> ty)
-  -> ColumnTypeExpression schemas ('Def :=> ty)
-default_ x ty = UnsafeColumnTypeExpression $
-  renderSQL ty <+> "DEFAULT" <+> renderExpression x
-
--- | not a true type, but merely a notational convenience for creating
--- unique identifier columns with type `PGint2`
-serial2, smallserial
-  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint2)
-serial2 = UnsafeColumnTypeExpression "serial2"
-smallserial = UnsafeColumnTypeExpression "smallserial"
--- | not a true type, but merely a notational convenience for creating
--- unique identifier columns with type `PGint4`
-serial4, serial
-  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint4)
-serial4 = UnsafeColumnTypeExpression "serial4"
-serial = UnsafeColumnTypeExpression "serial"
--- | not a true type, but merely a notational convenience for creating
--- unique identifier columns with type `PGint8`
-serial8, bigserial
-  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint8)
-serial8 = UnsafeColumnTypeExpression "serial8"
-bigserial = UnsafeColumnTypeExpression "bigserial"
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL/Expression/Type.hs b/squeal-postgresql/src/Squeal/PostgreSQL/Expression/Type.hs
index ccc4f94..ab51468 100644
--- a/squeal-postgresql/src/Squeal/PostgreSQL/Expression/Type.hs
+++ b/squeal-postgresql/src/Squeal/PostgreSQL/Expression/Type.hs
@@ -23,15 +23,16 @@ Type expressions.
   , ScopedTypeVariables
   , TypeApplications
   , TypeOperators
+  , UndecidableInstances
 #-}
 
 module Squeal.PostgreSQL.Expression.Type
-  ( TypeExpression (..)
-  , cast
+  ( -- * type casting
+    cast
   , astype
   , inferredtype
-  , PGTyped (..)
-  , FieldTyped (..)
+    -- * type expressions
+  , TypeExpression (..)
   , typedef
   , typetable
   , typeview
@@ -78,6 +79,22 @@ module Squeal.PostgreSQL.Expression.Type
   , tsrange
   , tstzrange
   , daterange
+    -- * column type definitions
+  , ColumnTypeExpression (..)
+  , nullable
+  , notNullable
+  , default_
+  , serial2
+  , smallserial
+  , serial4
+  , serial
+  , serial8
+  , bigserial
+  , hask
+    -- * type inference
+  , PGTyped (..)
+  , PGNullityTyped (..)
+  , FieldTyped (..)
   ) where
 
 import Control.DeepSeq
@@ -91,6 +108,7 @@ import qualified Generics.SOP as SOP
 
 import Squeal.PostgreSQL.Alias
 import Squeal.PostgreSQL.Expression
+import Squeal.PostgreSQL.PG
 import Squeal.PostgreSQL.Render
 import Squeal.PostgreSQL.Schema
 
@@ -132,6 +150,7 @@ astype = cast
 inferredtype
   :: PGTyped schemas ty
   => Expression outer common grp schemas params from ty
+  -- ^ value
   -> Expression outer common grp schemas params from ty
 inferredtype = astype pgtype
 
@@ -151,6 +170,7 @@ instance RenderSQL (TypeExpression schemas ty) where
 typedef
   :: (Has sch schemas schema, Has td schema ('Typedef ty))
   => QualifiedAlias sch td
+  -- ^ type alias
   -> TypeExpression schemas (null ty)
 typedef = UnsafeTypeExpression . renderSQL
 
@@ -159,6 +179,7 @@ typedef = UnsafeTypeExpression . renderSQL
 typetable
   :: (Has sch schemas schema, Has tab schema ('Table table))
   => QualifiedAlias sch tab
+  -- ^ table alias
   -> TypeExpression schemas (null ('PGcomposite (TableToRow table)))
 typetable = UnsafeTypeExpression . renderSQL
 
@@ -167,6 +188,7 @@ typetable = UnsafeTypeExpression . renderSQL
 typeview
   :: (Has sch schemas schema, Has vw schema ('View view))
   => QualifiedAlias sch vw
+  -- ^ view alias
   -> TypeExpression schemas (null ('PGcomposite view))
 typeview = UnsafeTypeExpression . renderSQL
 
@@ -353,3 +375,72 @@ class FieldTyped schemas ty where
 instance (KnownSymbol alias, PGTyped schemas ty)
   => FieldTyped schemas (alias ::: ty) where
     fieldtype = pgtype `As` Alias
+
+-- | `ColumnTypeExpression`s are used in `createTable` commands.
+newtype ColumnTypeExpression (schemas :: SchemasType) (ty :: ColumnType)
+  = UnsafeColumnTypeExpression { renderColumnTypeExpression :: ByteString }
+  deriving (GHC.Generic,Show,Eq,Ord,NFData)
+instance RenderSQL (ColumnTypeExpression schemas ty) where
+  renderSQL = renderColumnTypeExpression
+
+-- | used in `createTable` commands as a column constraint to note that
+-- @NULL@ may be present in a column
+nullable
+  :: TypeExpression schemas (nullity ty)
+  -> ColumnTypeExpression schemas ('NoDef :=> 'Null ty)
+nullable ty = UnsafeColumnTypeExpression $ renderSQL ty <+> "NULL"
+
+-- | used in `createTable` commands as a column constraint to ensure
+-- @NULL@ is not present in a column
+notNullable
+  :: TypeExpression schemas (nullity ty)
+  -> ColumnTypeExpression schemas ('NoDef :=> 'NotNull ty)
+notNullable ty = UnsafeColumnTypeExpression $ renderSQL ty <+> "NOT NULL"
+
+-- | used in `createTable` commands as a column constraint to give a default
+default_
+  :: Expression '[] '[] 'Ungrouped schemas '[] '[] ty
+  -> ColumnTypeExpression schemas ('NoDef :=> ty)
+  -> ColumnTypeExpression schemas ('Def :=> ty)
+default_ x ty = UnsafeColumnTypeExpression $
+  renderSQL ty <+> "DEFAULT" <+> renderExpression x
+
+-- | not a true type, but merely a notational convenience for creating
+-- unique identifier columns with type `PGint2`
+serial2, smallserial
+  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint2)
+serial2 = UnsafeColumnTypeExpression "serial2"
+smallserial = UnsafeColumnTypeExpression "smallserial"
+-- | not a true type, but merely a notational convenience for creating
+-- unique identifier columns with type `PGint4`
+serial4, serial
+  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint4)
+serial4 = UnsafeColumnTypeExpression "serial4"
+serial = UnsafeColumnTypeExpression "serial"
+-- | not a true type, but merely a notational convenience for creating
+-- unique identifier columns with type `PGint8`
+serial8, bigserial
+  :: ColumnTypeExpression schemas ('Def :=> 'NotNull 'PGint8)
+serial8 = UnsafeColumnTypeExpression "serial8"
+bigserial = UnsafeColumnTypeExpression "bigserial"
+
+-- | Like @PGTyped@ but also accounts for nullity.
+class PGNullityTyped schemas (nullty :: NullityType) where
+  pgNullityType :: ColumnTypeExpression schemas ('NoDef :=> nullty)
+
+instance PGTyped schemas ('Null ty) => PGNullityTyped schemas ('Null ty) where
+  pgNullityType = nullable (pgtype @_ @('Null ty))
+
+instance PGTyped schemas ('NotNull ty) => PGNullityTyped schemas ('NotNull ty) where
+  pgNullityType = notNullable (pgtype @_ @('NotNull ty))
+
+-- | Allow you to specify pg column types in relation to haskell types.
+-- >>> printSQL $ hask @(Maybe String)
+-- text NULL
+--
+-- >>> printSQL $ hask @Double
+-- float8 NOT NULL
+hask
+  :: forall hask schemas. PGNullityTyped schemas (NullPG hask)
+  => ColumnTypeExpression schemas ('NoDef :=> NullPG hask)
+hask = pgNullityType
diff --git a/squeal-postgresql/src/Squeal/PostgreSQL/Migration.hs b/squeal-postgresql/src/Squeal/PostgreSQL/Migration.hs
index 2cc2be1..8945425 100644
--- a/squeal-postgresql/src/Squeal/PostgreSQL/Migration.hs
+++ b/squeal-postgresql/src/Squeal/PostgreSQL/Migration.hs
@@ -168,7 +168,6 @@ import Squeal.PostgreSQL.Alias
 import Squeal.PostgreSQL.Binary
 import Squeal.PostgreSQL.Definition
 import Squeal.PostgreSQL.Definition.Table
-import Squeal.PostgreSQL.Definition.Table.Column
 import Squeal.PostgreSQL.Definition.Table.Constraint
 import Squeal.PostgreSQL.Expression.Comparison
 import Squeal.PostgreSQL.Expression.Parameter