diff --git a/.eslintrc.json b/.eslintrc.json
index 84cef4f..1c6afb9 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -1,11 +1,9 @@
 {
   "parserOptions": {
-    "ecmaVersion": 5
+    "ecmaVersion": 6,
+    "sourceType": "module"
   },
   "extends": "eslint:recommended",
-  "env": {
-    "commonjs": true
-  },
   "rules": {
     "strict": [2, "global"],
     "block-scoped-var": 2,
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 43d2897..b6ebf3a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,6 +13,8 @@ jobs:
       - uses: actions/checkout@v2
 
       - uses: purescript-contrib/setup-purescript@main
+        with:
+          purescript: "unstable"
 
       - uses: actions/setup-node@v1
         with:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c3bf386..d63cbd2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,8 @@ Notable changes to this project are documented in this file. The format is based
 ## [Unreleased]
 
 Breaking changes:
+- Migrate FFI to ES modules (#158 by @kl0tl and @JordanMartinez)
+- Replaced polymorphic proxies with monomorphic `Proxy` (#158 by @JordanMartinez)
 
 New features:
 
diff --git a/bower.json b/bower.json
index d4c9f36..2b8dd58 100644
--- a/bower.json
+++ b/bower.json
@@ -16,26 +16,26 @@
     "package.json"
   ],
   "dependencies": {
-    "purescript-arrays": "^6.0.0",
-    "purescript-control": "^5.0.0",
-    "purescript-either": "^5.0.0",
-    "purescript-enums": "^5.0.0",
-    "purescript-foldable-traversable": "^5.0.0",
-    "purescript-gen": "^3.0.0",
-    "purescript-integers": "^5.0.0",
-    "purescript-maybe": "^5.0.0",
-    "purescript-newtype": "^4.0.0",
-    "purescript-nonempty": "^6.0.0",
-    "purescript-partial": "^3.0.0",
-    "purescript-prelude": "^5.0.0",
-    "purescript-tailrec": "^5.0.0",
-    "purescript-tuples": "^6.0.0",
-    "purescript-unfoldable": "^5.0.0",
-    "purescript-unsafe-coerce": "^5.0.0"
+    "purescript-arrays": "master",
+    "purescript-control": "master",
+    "purescript-either": "master",
+    "purescript-enums": "master",
+    "purescript-foldable-traversable": "master",
+    "purescript-gen": "master",
+    "purescript-integers": "master",
+    "purescript-maybe": "master",
+    "purescript-newtype": "master",
+    "purescript-nonempty": "master",
+    "purescript-partial": "master",
+    "purescript-prelude": "master",
+    "purescript-tailrec": "master",
+    "purescript-tuples": "master",
+    "purescript-unfoldable": "master",
+    "purescript-unsafe-coerce": "master"
   },
   "devDependencies": {
-    "purescript-assert": "^5.0.0",
-    "purescript-console": "^5.0.0",
-    "purescript-minibench": "^3.0.0"
+    "purescript-assert": "master",
+    "purescript-console": "master",
+    "purescript-minibench": "master"
   }
 }
diff --git a/package.json b/package.json
index c116cae..cffd45e 100644
--- a/package.json
+++ b/package.json
@@ -4,15 +4,15 @@
     "clean": "rimraf output && rimraf .pulp-cache",
     "build": "eslint src && pulp build -- --censor-lib --strict",
     "test": "pulp test && npm run test:run:without_codePointAt",
-    "test:run:without_codePointAt": "node -e \"delete String.prototype.codePointAt; require('./output/Test.Main/index.js').main();\"",
+    "test:run:without_codePointAt": "node -e \"delete String.prototype.codePointAt; import('./output/Test.Main/index.js').then(m => m.main());\"",
     "bench:build": "purs compile 'bench/**/*.purs' 'src/**/*.purs' 'bower_components/*/src/**/*.purs'",
     "bench:run": "node --expose-gc -e 'require(\"./output/Bench.Main/index.js\").main()'",
     "bench": "npm run bench:build && npm run bench:run"
   },
   "devDependencies": {
     "eslint": "^7.15.0",
-    "pulp": "^15.0.0",
-    "purescript-psa": "^0.8.0",
+    "pulp": "16.0.0-0",
+    "purescript-psa": "^0.8.2",
     "rimraf": "^3.0.2"
   }
 }
diff --git a/src/Data/String/CodePoints.js b/src/Data/String/CodePoints.js
index eead7f6..ebd9e39 100644
--- a/src/Data/String/CodePoints.js
+++ b/src/Data/String/CodePoints.js
@@ -1,4 +1,3 @@
-"use strict";
 /* global Symbol */
 
 var hasArrayFrom = typeof Array.from === "function";
@@ -10,13 +9,13 @@ var hasStringIterator =
 var hasFromCodePoint = typeof String.prototype.fromCodePoint === "function";
 var hasCodePointAt = typeof String.prototype.codePointAt === "function";
 
-exports._unsafeCodePointAt0 = function (fallback) {
+export const _unsafeCodePointAt0 = function (fallback) {
   return hasCodePointAt
     ? function (str) { return str.codePointAt(0); }
     : fallback;
 };
 
-exports._codePointAt = function (fallback) {
+export const _codePointAt = function (fallback) {
   return function (Just) {
     return function (Nothing) {
       return function (unsafeCodePointAt0) {
@@ -40,7 +39,7 @@ exports._codePointAt = function (fallback) {
   };
 };
 
-exports._countPrefix = function (fallback) {
+export const _countPrefix = function (fallback) {
   return function (unsafeCodePointAt0) {
     if (hasStringIterator) {
       return function (pred) {
@@ -59,7 +58,7 @@ exports._countPrefix = function (fallback) {
   };
 };
 
-exports._fromCodePointArray = function (singleton) {
+export const _fromCodePointArray = function (singleton) {
   return hasFromCodePoint
     ? function (cps) {
       // Function.prototype.apply will fail for very large second parameters,
@@ -74,11 +73,11 @@ exports._fromCodePointArray = function (singleton) {
     };
 };
 
-exports._singleton = function (fallback) {
+export const _singleton = function (fallback) {
   return hasFromCodePoint ? String.fromCodePoint : fallback;
 };
 
-exports._take = function (fallback) {
+export const _take = function (fallback) {
   return function (n) {
     if (hasStringIterator) {
       return function (str) {
@@ -96,7 +95,7 @@ exports._take = function (fallback) {
   };
 };
 
-exports._toCodePointArray = function (fallback) {
+export const _toCodePointArray = function (fallback) {
   return function (unsafeCodePointAt0) {
     if (hasArrayFrom) {
       return function (str) {
diff --git a/src/Data/String/CodeUnits.js b/src/Data/String/CodeUnits.js
index 6017fd3..47d61f9 100644
--- a/src/Data/String/CodeUnits.js
+++ b/src/Data/String/CodeUnits.js
@@ -1,18 +1,16 @@
-"use strict";
-
-exports.fromCharArray = function (a) {
+export const fromCharArray = function (a) {
   return a.join("");
 };
 
-exports.toCharArray = function (s) {
+export const toCharArray = function (s) {
   return s.split("");
 };
 
-exports.singleton = function (c) {
+export const singleton = function (c) {
   return c;
 };
 
-exports._charAt = function (just) {
+export const _charAt = function (just) {
   return function (nothing) {
     return function (i) {
       return function (s) {
@@ -22,7 +20,7 @@ exports._charAt = function (just) {
   };
 };
 
-exports._toChar = function (just) {
+export const _toChar = function (just) {
   return function (nothing) {
     return function (s) {
       return s.length === 1 ? just(s) : nothing;
@@ -30,11 +28,11 @@ exports._toChar = function (just) {
   };
 };
 
-exports.length = function (s) {
+export const length = function (s) {
   return s.length;
 };
 
-exports.countPrefix = function (p) {
+export const countPrefix = function (p) {
   return function (s) {
     var i = 0;
     while (i < s.length && p(s.charAt(i))) i++;
@@ -42,7 +40,7 @@ exports.countPrefix = function (p) {
   };
 };
 
-exports._indexOf = function (just) {
+export const _indexOf = function (just) {
   return function (nothing) {
     return function (x) {
       return function (s) {
@@ -53,7 +51,7 @@ exports._indexOf = function (just) {
   };
 };
 
-exports._indexOfStartingAt = function (just) {
+export const _indexOfStartingAt = function (just) {
   return function (nothing) {
     return function (x) {
       return function (startAt) {
@@ -67,7 +65,7 @@ exports._indexOfStartingAt = function (just) {
   };
 };
 
-exports._lastIndexOf = function (just) {
+export const _lastIndexOf = function (just) {
   return function (nothing) {
     return function (x) {
       return function (s) {
@@ -78,7 +76,7 @@ exports._lastIndexOf = function (just) {
   };
 };
 
-exports._lastIndexOfStartingAt = function (just) {
+export const _lastIndexOfStartingAt = function (just) {
   return function (nothing) {
     return function (x) {
       return function (startAt) {
@@ -91,19 +89,19 @@ exports._lastIndexOfStartingAt = function (just) {
   };
 };
 
-exports.take = function (n) {
+export const take = function (n) {
   return function (s) {
     return s.substr(0, n);
   };
 };
 
-exports.drop = function (n) {
+export const drop = function (n) {
   return function (s) {
     return s.substring(n);
   };
 };
 
-exports._slice = function (b) {
+export const _slice = function (b) {
   return function (e) {
     return function (s) {
       return s.slice(b,e);
@@ -111,7 +109,7 @@ exports._slice = function (b) {
   };
 };
 
-exports.splitAt = function (i) {
+export const splitAt = function (i) {
   return function (s) {
     return { before: s.substring(0, i), after: s.substring(i) };
   };
diff --git a/src/Data/String/Common.js b/src/Data/String/Common.js
index 111c02e..5693585 100644
--- a/src/Data/String/Common.js
+++ b/src/Data/String/Common.js
@@ -1,6 +1,4 @@
-"use strict";
-
-exports._localeCompare = function (lt) {
+export const _localeCompare = function (lt) {
   return function (eq) {
     return function (gt) {
       return function (s1) {
@@ -13,7 +11,7 @@ exports._localeCompare = function (lt) {
   };
 };
 
-exports.replace = function (s1) {
+export const replace = function (s1) {
   return function (s2) {
     return function (s3) {
       return s3.replace(s1, s2);
@@ -21,7 +19,7 @@ exports.replace = function (s1) {
   };
 };
 
-exports.replaceAll = function (s1) {
+export const replaceAll = function (s1) {
   return function (s2) {
     return function (s3) {
       return s3.replace(new RegExp(s1.replace(/[-\/\\^$*+?.()|[\]{}]/g, "\\$&"), "g"), s2); // eslint-disable-line no-useless-escape
@@ -29,25 +27,25 @@ exports.replaceAll = function (s1) {
   };
 };
 
-exports.split = function (sep) {
+export const split = function (sep) {
   return function (s) {
     return s.split(sep);
   };
 };
 
-exports.toLower = function (s) {
+export const toLower = function (s) {
   return s.toLowerCase();
 };
 
-exports.toUpper = function (s) {
+export const toUpper = function (s) {
   return s.toUpperCase();
 };
 
-exports.trim = function (s) {
+export const trim = function (s) {
   return s.trim();
 };
 
-exports.joinWith = function (s) {
+export const joinWith = function (s) {
   return function (xs) {
     return xs.join(s);
   };
diff --git a/src/Data/String/NonEmpty/Internal.purs b/src/Data/String/NonEmpty/Internal.purs
index 707b779..8722654 100644
--- a/src/Data/String/NonEmpty/Internal.purs
+++ b/src/Data/String/NonEmpty/Internal.purs
@@ -16,6 +16,7 @@ import Data.String as String
 import Data.String.Pattern (Pattern)
 import Data.Symbol (class IsSymbol, reflectSymbol)
 import Prim.TypeError as TE
+import Type.Proxy (Proxy)
 import Unsafe.Coerce (unsafeCoerce)
 
 -- | A string that is known not to be empty.
@@ -41,7 +42,7 @@ instance showNonEmptyString :: Show NonEmptyString where
 -- | something = nes (Proxy :: Proxy "something")
 -- | ```
 class MakeNonEmpty (s :: Symbol) where
-  nes :: forall proxy. proxy s -> NonEmptyString
+  nes :: Proxy s -> NonEmptyString
 
 instance makeNonEmptyBad :: TE.Fail (TE.Text "Cannot create an NonEmptyString from an empty Symbol") => MakeNonEmpty "" where
   nes _ = NonEmptyString ""
diff --git a/src/Data/String/Regex.js b/src/Data/String/Regex.js
index b3be593..3196034 100644
--- a/src/Data/String/Regex.js
+++ b/src/Data/String/Regex.js
@@ -1,10 +1,8 @@
-"use strict";
-
-exports.showRegexImpl = function (r) {
+export const showRegexImpl = function (r) {
   return "" + r;
 };
 
-exports.regexImpl = function (left) {
+export const regexImpl = function (left) {
   return function (right) {
     return function (s1) {
       return function (s2) {
@@ -18,11 +16,11 @@ exports.regexImpl = function (left) {
   };
 };
 
-exports.source = function (r) {
+export const source = function (r) {
   return r.source;
 };
 
-exports.flagsImpl = function (r) {
+export const flagsImpl = function (r) {
   return {
     multiline: r.multiline,
     ignoreCase: r.ignoreCase,
@@ -33,7 +31,7 @@ exports.flagsImpl = function (r) {
   };
 };
 
-exports.test = function (r) {
+export const test = function (r) {
   return function (s) {
     var lastIndex = r.lastIndex;
     var result = r.test(s);
@@ -42,7 +40,7 @@ exports.test = function (r) {
   };
 };
 
-exports._match = function (just) {
+export const _match = function (just) {
   return function (nothing) {
     return function (r) {
       return function (s) {
@@ -60,7 +58,7 @@ exports._match = function (just) {
   };
 };
 
-exports.replace = function (r) {
+export const replace = function (r) {
   return function (s1) {
     return function (s2) {
       return s2.replace(r, s1);
@@ -68,7 +66,7 @@ exports.replace = function (r) {
   };
 };
 
-exports._replaceBy = function (just) {
+export const _replaceBy = function (just) {
   return function (nothing) {
     return function (r) {
       return function (f) {
@@ -87,7 +85,7 @@ exports._replaceBy = function (just) {
   };
 };
 
-exports._search = function (just) {
+export const _search = function (just) {
   return function (nothing) {
     return function (r) {
       return function (s) {
@@ -98,7 +96,7 @@ exports._search = function (just) {
   };
 };
 
-exports.split = function (r) {
+export const split = function (r) {
   return function (s) {
     return s.split(r);
   };
diff --git a/src/Data/String/Unsafe.js b/src/Data/String/Unsafe.js
index d7a17ca..75772aa 100644
--- a/src/Data/String/Unsafe.js
+++ b/src/Data/String/Unsafe.js
@@ -1,13 +1,11 @@
-"use strict";
-
-exports.charAt = function (i) {
+export const charAt = function (i) {
   return function (s) {
     if (i >= 0 && i < s.length) return s.charAt(i);
     throw new Error("Data.String.Unsafe.charAt: Invalid index.");
   };
 };
 
-exports.char = function (s) {
+export const char = function (s) {
   if (s.length === 1) return s.charAt(0);
   throw new Error("Data.String.Unsafe.char: Expected string of length 1.");
 };
diff --git a/test/Test/Data/String/NonEmpty/CodeUnits.purs b/test/Test/Data/String/NonEmpty/CodeUnits.purs
index 9a33b0c..e810dd9 100644
--- a/test/Test/Data/String/NonEmpty/CodeUnits.purs
+++ b/test/Test/Data/String/NonEmpty/CodeUnits.purs
@@ -170,11 +170,11 @@ testNonEmptyStringCodeUnits = do
 
   log "takeWhile"
   assertEqual
-    { actual: NESCU.takeWhile (\c -> true) (nes (Proxy :: Proxy "abc"))
+    { actual: NESCU.takeWhile (\_ -> true) (nes (Proxy :: Proxy "abc"))
     , expected: Just (nes (Proxy :: Proxy "abc"))
     }
   assertEqual
-    { actual: NESCU.takeWhile (\c -> false) (nes (Proxy :: Proxy "abc"))
+    { actual: NESCU.takeWhile (\_ -> false) (nes (Proxy :: Proxy "abc"))
     , expected: Nothing
     }
   assertEqual
@@ -192,11 +192,11 @@ testNonEmptyStringCodeUnits = do
 
   log "dropWhile"
   assertEqual
-    { actual: NESCU.dropWhile (\c -> true) (nes (Proxy :: Proxy "abc"))
+    { actual: NESCU.dropWhile (\_ -> true) (nes (Proxy :: Proxy "abc"))
     , expected: Nothing
     }
   assertEqual
-    { actual: NESCU.dropWhile (\c -> false) (nes (Proxy :: Proxy "abc"))
+    { actual: NESCU.dropWhile (\_ -> false) (nes (Proxy :: Proxy "abc"))
     , expected: Just (nes (Proxy :: Proxy "abc"))
     }
   assertEqual