diff --git a/.gitignore b/.gitignore
index 7050558..332b6cf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@
 /bower_components/
 /node_modules/
 /output/
+package-lock.json
diff --git a/LICENSE b/LICENSE
index 58b0299..311379c 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,20 +1,26 @@
-The MIT License (MIT)
+Copyright 2018 PureScript
 
-Copyright (c) 2014 PureScript
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
 
-Permission is hereby granted, free of charge, to any person obtaining a copy of
-this software and associated documentation files (the "Software"), to deal in
-the Software without restriction, including without limitation the rights to
-use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
-the Software, and to permit persons to whom the Software is furnished to do so,
-subject to the following conditions:
+1. Redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.
 
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
+2. Redistributions in binary form must reproduce the above copyright notice,
+this list of conditions and the following disclaimer in the documentation and/or
+other materials provided with the distribution.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
-FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
-COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
-IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
-CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+3. Neither the name of the copyright holder nor the names of its contributors
+may be used to endorse or promote products derived from this software without
+specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/bower.json b/bower.json
index 4a2a46b..60d8a13 100644
--- a/bower.json
+++ b/bower.json
@@ -1,7 +1,6 @@
 {
   "name": "purescript-foreign",
   "homepage": "https://github.com/purescript/purescript-foreign",
-  "description": "PureScript library for dealing with foreign data (JSON and JavaScript objects)",
   "authors": [
     "Gary Burgess <gary.burgess@gmail.com>",
     "Phil Freeman <paf31@cantab.net>"
@@ -10,7 +9,7 @@
     "type": "git",
     "url": "git://github.com/purescript/purescript-foreign.git"
   },
-  "license": "MIT",
+  "license": "BSD-3-Clause",
   "ignore": [
     "**/.*",
     "bower_components",
@@ -21,16 +20,17 @@
     "package.json"
   ],
   "dependencies": {
-    "purescript-arrays": "^4.0.0",
-    "purescript-either": "^3.0.0",
-    "purescript-foldable-traversable": "^3.0.0",
-    "purescript-functions": "^3.0.0",
-    "purescript-integers": "^3.0.0",
-    "purescript-lists": "^4.0.0",
-    "purescript-strings": "^3.0.0",
-    "purescript-transformers": "^3.0.0"
+    "purescript-either": "^4.0.0",
+    "purescript-functions": "^4.0.0",
+    "purescript-identity": "^4.0.0",
+    "purescript-integers": "^4.0.0",
+    "purescript-lists": "^5.0.0",
+    "purescript-maybe": "^4.0.0",
+    "purescript-prelude": "^4.0.0",
+    "purescript-strings": "^4.0.0",
+    "purescript-transformers": "^4.0.0"
   },
   "devDependencies": {
-    "purescript-console": "^3.0.0"
+    "purescript-console": "^4.0.0"
   }
 }
diff --git a/examples/Applicative.purs b/examples/Applicative.purs
index ed082b9..9f9f5c3 100755
--- a/examples/Applicative.purs
+++ b/examples/Applicative.purs
@@ -2,14 +2,12 @@ module Example.Applicative where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readNumber)
-import Data.Foreign.Index ((!))
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readNumber)
+import Foreign.Index ((!))
 
 data Point = Point Number Number Number
 
@@ -23,7 +21,7 @@ readPoint value = do
     <*> (value ! "y" >>= readNumber)
     <*> (value ! "z" >>= readNumber)
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main =
   logShow $ runExcept $
     readPoint =<< foreignValue """{ "x": 1, "y": 2, "z": 3 }"""
diff --git a/examples/Arrays.purs b/examples/Arrays.purs
index 25bb108..86efd36 100644
--- a/examples/Arrays.purs
+++ b/examples/Arrays.purs
@@ -2,16 +2,14 @@ module Example.Arrays where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (readArray, readNumber, readString)
 import Data.Traversable (traverse)
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (readArray, readNumber, readString)
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
   logShow $ runExcept $
     traverse readString =<< readArray =<< foreignValue """["hello", "world"]"""
diff --git a/examples/Complex.purs b/examples/Complex.purs
index 4093181..0a96a4d 100755
--- a/examples/Complex.purs
+++ b/examples/Complex.purs
@@ -2,32 +2,21 @@ module Example.Complex where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readArray, readBoolean, readNumber, readString, readNullOrUndefined)
-import Data.Foreign.Index ((!))
-import Data.Traversable (traverse)
 import Data.Maybe (Maybe)
-
+import Data.Traversable (traverse)
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readArray, readBoolean, readNumber, readString, readNullOrUndefined)
+import Foreign.Index ((!))
 
-newtype SomeObject =
-  SomeObject
-    { foo :: String
-    , bar :: Boolean
-    , baz :: Number
-    , list :: Array ListItem
-    }
-
-instance showSomeObject :: Show SomeObject where
-  show (SomeObject o) =
-    "(SomeObject { foo: " <> show o.foo <>
-    ", bar: " <> show o.bar <>
-    ", baz: " <> show o.baz <>
-    ", list: " <> show o.list <>
-    "})"
+type SomeObject =
+  { foo :: String
+  , bar :: Boolean
+  , baz :: Number
+  , list :: Array ListItem
+  }
 
 readSomeObject :: Foreign -> F SomeObject
 readSomeObject value = do
@@ -35,30 +24,22 @@ readSomeObject value = do
   bar <- value ! "bar" >>= readBoolean
   baz <- value ! "baz" >>= readNumber
   list <- value ! "list" >>= readArray >>= traverse readListItem
-  pure $ SomeObject { foo, bar, baz, list }
-
-newtype ListItem =
-  ListItem
-    { x :: Number
-    , y :: Number
-    , z :: Maybe Number
-    }
+  pure { foo, bar, baz, list }
 
-instance showListItem :: Show ListItem where
-  show (ListItem o) =
-    "(ListItem { x: " <> show o.x <>
-    ", y: " <> show o.y <>
-    ", z: " <> show o.z <>
-    " })"
+type ListItem =
+  { x :: Number
+  , y :: Number
+  , z :: Maybe Number
+  }
 
 readListItem :: Foreign -> F ListItem
 readListItem value = do
   x <- value ! "x" >>= readNumber
   y <- value ! "y" >>= readNumber
   z <- value ! "z" >>= readNullOrUndefined >>= traverse readNumber
-  pure $ ListItem { x, y, z }
+  pure { x, y, z }
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
   let json = """{"foo":"hello","bar":true,"baz":1,"list":[{"x":1,"y":2},{"x":3,"y":4,"z":999}]}"""
   logShow $ runExcept $ readSomeObject =<< foreignValue json
diff --git a/examples/MaybeNullable.purs b/examples/MaybeNullable.purs
index d9bd790..1831663 100755
--- a/examples/MaybeNullable.purs
+++ b/examples/MaybeNullable.purs
@@ -2,18 +2,18 @@ module Example.MaybeNullable where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
+import Effect (Effect)
+import Effect.Console (logShow)
 import Control.Monad.Except (runExcept)
 
-import Data.Foreign (readBoolean, readNull)
+import Foreign (readBoolean, readNull)
 import Data.Traversable (traverse)
 
 import Example.Util.Value (foreignValue)
 
 -- Parsing values that are allowed to null or undefined is possible by
 -- using Maybe types.
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
   logShow $ runExcept $
     traverse readBoolean =<< readNull =<< foreignValue "null"
diff --git a/examples/Nested.purs b/examples/Nested.purs
index 3a04216..bbcb3e4 100755
--- a/examples/Nested.purs
+++ b/examples/Nested.purs
@@ -2,14 +2,12 @@ module Example.Nested where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readNumber, readString)
-import Data.Foreign.Index ((!))
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readNumber, readString)
+import Foreign.Index ((!))
 
 data Foo = Foo Bar Baz
 
@@ -32,7 +30,7 @@ readFoo value = do
   n <- value ! "foo" ! "baz" >>= readNumber
   pure $ Foo (Bar s) (Baz n)
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main =
   logShow $ runExcept $
     readFoo =<< foreignValue """{ "foo": { "bar": "bar", "baz": 1 } }"""
diff --git a/examples/Objects.purs b/examples/Objects.purs
index 0fa094e..3a9893b 100755
--- a/examples/Objects.purs
+++ b/examples/Objects.purs
@@ -2,28 +2,22 @@ module Example.Objects where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readNumber)
-import Data.Foreign.Index ((!))
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readNumber)
+import Foreign.Index ((!))
 
-newtype Point = Point { x :: Number, y :: Number }
-
-instance showPoint :: Show Point where
-  show (Point { x, y }) =
-    "(Point { x: " <> show x <> ", y: " <> show y <> " })"
+type Point = { x :: Number, y :: Number }
 
 readPoint :: Foreign -> F Point
 readPoint value = do
   x <- value ! "x" >>= readNumber
   y <- value ! "y" >>= readNumber
-  pure $ Point { x, y }
+  pure { x, y }
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
   logShow $ runExcept $
     readPoint =<< foreignValue """{ "x": 1, "y": 2 }"""
diff --git a/examples/ParseErrors.purs b/examples/ParseErrors.purs
index a3418c9..52faf30 100755
--- a/examples/ParseErrors.purs
+++ b/examples/ParseErrors.purs
@@ -2,15 +2,13 @@ module Example.ParseErrors where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readArray, readBoolean, readNumber, readString)
-import Data.Foreign.Index ((!))
 import Data.Traversable (traverse)
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readArray, readBoolean, readNumber, readString)
+import Foreign.Index ((!))
 
 newtype Point = Point { x :: Number, y :: Number }
 
@@ -23,7 +21,7 @@ readPoint value = do
   y <- value ! "y" >>= readNumber
   pure $ Point { x: x, y: y }
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
 
   -- When trying to parse invalid JSON we catch an exception from
diff --git a/examples/SimpleTypes.purs b/examples/SimpleTypes.purs
index 97233d7..e3ba48c 100644
--- a/examples/SimpleTypes.purs
+++ b/examples/SimpleTypes.purs
@@ -2,17 +2,15 @@ module Example.SimpleTypes where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (readString, readNumber, readBoolean)
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (readString, readNumber, readBoolean)
 
 -- Parsing of the simple JSON String, Number and Boolean types is provided
 -- out of the box.
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
   logShow $ runExcept $
     readString =<< foreignValue "\"a JSON string\""
diff --git a/examples/Union.purs b/examples/Union.purs
index ff9a56b..06504da 100755
--- a/examples/Union.purs
+++ b/examples/Union.purs
@@ -2,14 +2,12 @@ module Example.Union where
 
 import Prelude
 
-import Control.Monad.Eff (Eff)
-import Control.Monad.Eff.Console (CONSOLE, logShow)
 import Control.Monad.Except (runExcept)
-
-import Data.Foreign (F, Foreign, readBoolean, readString)
-import Data.Foreign.Index ((!))
-
+import Effect (Effect)
+import Effect.Console (logShow)
 import Example.Util.Value (foreignValue)
+import Foreign (F, Foreign, readBoolean, readString)
+import Foreign.Index ((!))
 
 data StringList = Nil | Cons String StringList
 
@@ -28,7 +26,7 @@ readStringList value =
           <$> (value ! "head" >>= readString)
           <*> (value ! "tail" >>= readStringList)
 
-main :: Eff (console :: CONSOLE) Unit
+main :: Effect Unit
 main = do
 
   logShow $ runExcept $
diff --git a/examples/Util/Value.purs b/examples/Util/Value.purs
index bc6516e..50f7b8f 100644
--- a/examples/Util/Value.purs
+++ b/examples/Util/Value.purs
@@ -4,9 +4,9 @@ import Prelude
 
 import Data.Function.Uncurried (Fn3, runFn3)
 
-import Data.Foreign (F, Foreign, ForeignError(..), fail)
+import Foreign (F, Foreign, ForeignError(..), fail)
 
 foreign import foreignValueImpl :: forall r. Fn3 (String -> r) (Foreign -> r) String r
 
 foreignValue :: String -> F Foreign
-foreignValue json = runFn3 foreignValueImpl (fail <<< JSONError) pure json
+foreignValue json = runFn3 foreignValueImpl (fail <<< ForeignError) pure json
diff --git a/package.json b/package.json
index e499ea4..f517f7c 100644
--- a/package.json
+++ b/package.json
@@ -6,9 +6,9 @@
     "test": "pulp build -I examples -- --censor-lib --strict"
   },
   "devDependencies": {
-    "eslint": "^3.17.1",
-    "pulp": "^10.0.4",
-    "purescript-psa": "^0.5.0-rc.1",
-    "rimraf": "^2.6.1"
+    "eslint": "^4.19.1",
+    "pulp": "^12.2.0",
+    "purescript-psa": "^0.6.0",
+    "rimraf": "^2.6.2"
   }
 }
diff --git a/src/Data/Foreign.js b/src/Foreign.js
similarity index 92%
rename from src/Data/Foreign.js
rename to src/Foreign.js
index e511096..cb96c82 100644
--- a/src/Data/Foreign.js
+++ b/src/Foreign.js
@@ -1,6 +1,6 @@
 "use strict";
 
-exports.toForeign = function (value) {
+exports.unsafeToForeign = function (value) {
   return value;
 };
 
diff --git a/src/Data/Foreign.purs b/src/Foreign.purs
similarity index 90%
rename from src/Data/Foreign.purs
rename to src/Foreign.purs
index a7ea0df..2752c6e 100644
--- a/src/Data/Foreign.purs
+++ b/src/Foreign.purs
@@ -1,13 +1,13 @@
 -- | This module defines types and functions for working with _foreign_
 -- | data.
 
-module Data.Foreign
+module Foreign
   ( Foreign
   , ForeignError(..)
   , MultipleErrors(..)
   , F
   , renderForeignError
-  , toForeign
+  , unsafeToForeign
   , unsafeFromForeign
   , unsafeReadTagged
   , typeOf
@@ -36,7 +36,7 @@ import Data.Int as Int
 import Data.List.NonEmpty (NonEmptyList)
 import Data.List.NonEmpty as NEL
 import Data.Maybe (Maybe(..), maybe)
-import Data.String (toChar)
+import Data.String.CodeUnits (toChar)
 
 -- | A type for _foreign data_.
 -- |
@@ -56,7 +56,6 @@ data ForeignError
   | TypeMismatch String String
   | ErrorAtIndex Int ForeignError
   | ErrorAtProperty String ForeignError
-  | JSONError String
 
 derive instance eqForeignError :: Eq ForeignError
 derive instance ordForeignError :: Ord ForeignError
@@ -65,7 +64,6 @@ instance showForeignError :: Show ForeignError where
   show (ForeignError msg) = "(ForeignError " <> show msg <> ")"
   show (ErrorAtIndex i e) = "(ErrorAtIndex " <> show i <> " " <> show e <> ")"
   show (ErrorAtProperty prop e) = "(ErrorAtProperty " <> show prop <> " " <> show e <> ")"
-  show (JSONError s) = "(JSONError " <> show s <> ")"
   show (TypeMismatch exps act) = "(TypeMismatch " <> show exps <> " " <> show act <> ")"
 
 -- | A type for accumulating multiple `ForeignError`s.
@@ -73,9 +71,8 @@ type MultipleErrors = NonEmptyList ForeignError
 
 renderForeignError :: ForeignError -> String
 renderForeignError (ForeignError msg) = msg
-renderForeignError (ErrorAtIndex i e) = "Error at array index " <> show i <> ": " <> show e
-renderForeignError (ErrorAtProperty prop e) = "Error at property " <> show prop <> ": " <> show e
-renderForeignError (JSONError s) = "JSON error: " <> s
+renderForeignError (ErrorAtIndex i e) = "Error at array index " <> show i <> ": " <> renderForeignError e
+renderForeignError (ErrorAtProperty prop e) = "Error at property " <> show prop <> ": " <> renderForeignError e
 renderForeignError (TypeMismatch exp act) = "Type mismatch: expected " <> exp <> ", found " <> act
 
 -- | An error monad, used in this library to encode possible failures when
@@ -86,7 +83,12 @@ renderForeignError (TypeMismatch exp act) = "Type mismatch: expected " <> exp <>
 type F = Except MultipleErrors
 
 -- | Coerce any value to the a `Foreign` value.
-foreign import toForeign :: forall a. a -> Foreign
+-- |
+-- | This is considered unsafe as it's only intended to be used on primitive
+-- | JavaScript types, rather than PureScript types. Exporting PureScript values
+-- | via the FFI can be dangerous as they can be mutated by code outside the
+-- | PureScript program, resulting in difficult to diagnose problems elsewhere.
+foreign import unsafeToForeign :: forall a. a -> Foreign
 
 -- | Unsafely coerce a `Foreign` value.
 foreign import unsafeFromForeign :: forall a. Foreign -> a
diff --git a/src/Data/Foreign/Index.js b/src/Foreign/Index.js
similarity index 100%
rename from src/Data/Foreign/Index.js
rename to src/Foreign/Index.js
diff --git a/src/Data/Foreign/Index.purs b/src/Foreign/Index.purs
similarity index 95%
rename from src/Data/Foreign/Index.purs
rename to src/Foreign/Index.purs
index 71afb61..405e72f 100644
--- a/src/Data/Foreign/Index.purs
+++ b/src/Foreign/Index.purs
@@ -1,7 +1,7 @@
 -- | This module defines a type class for types which act like
 -- | _property indices_.
 
-module Data.Foreign.Index
+module Foreign.Index
   ( class Index
   , class Indexable
   , readProp
@@ -17,7 +17,7 @@ import Prelude
 
 import Control.Monad.Except.Trans (ExceptT)
 
-import Data.Foreign (Foreign, F, ForeignError(..), typeOf, isUndefined, isNull, fail)
+import Foreign (Foreign, F, ForeignError(..), typeOf, isUndefined, isNull, fail)
 import Data.Function.Uncurried (Fn2, runFn2, Fn4, runFn4)
 import Data.Identity (Identity)
 import Data.List.NonEmpty (NonEmptyList)
diff --git a/src/Data/Foreign/Keys.js b/src/Foreign/Keys.js
similarity index 100%
rename from src/Data/Foreign/Keys.js
rename to src/Foreign/Keys.js
diff --git a/src/Data/Foreign/Keys.purs b/src/Foreign/Keys.purs
similarity index 82%
rename from src/Data/Foreign/Keys.purs
rename to src/Foreign/Keys.purs
index 4bb9967..c600be1 100644
--- a/src/Data/Foreign/Keys.purs
+++ b/src/Foreign/Keys.purs
@@ -1,13 +1,13 @@
 -- | This module provides functions for working with object properties
 -- | of Javascript objects.
 
-module Data.Foreign.Keys
+module Foreign.Keys
   ( keys
   ) where
 
 import Prelude
 
-import Data.Foreign (F, Foreign, ForeignError(..), typeOf, isUndefined, isNull, fail)
+import Foreign (F, Foreign, ForeignError(..), typeOf, isUndefined, isNull, fail)
 
 foreign import unsafeKeys :: Foreign -> Array String