diff --git a/index.js b/index.js
index 1e9fc7d9..1604964e 100644
--- a/index.js
+++ b/index.js
@@ -25,7 +25,7 @@
 //. Sanctuary gives us a fighting chance of avoiding such errors. We might
 //. write:
 //.
-//.     R.map(S.toUpper, S.head(words))
+//.     S.map(S.toUpper, S.head(words))
 //.
 //. Sanctuary is designed to work in Node.js and in ES5-compatible browsers.
 //.
@@ -38,12 +38,6 @@
 //. That is, it takes an argument of type `Number` and returns a value of
 //. type `Number`.
 //.
-//. [`R.map`][R.map] has type `(a -> b) -> Array a -> Array b`. That is,
-//. it takes an argument of type `a -> b` and returns a value of type
-//. `Array a -> Array b`. `a` and `b` are type variables: applying `R.map`
-//. to a value of type `String -> Number` will result in a value of type
-//. `Array String -> Array Number`.
-//.
 //. Sanctuary embraces types. JavaScript doesn't support algebraic data types,
 //. but these can be simulated by providing a group of data constructors which
 //. return values with the same set of methods. A value of the Either type, for
@@ -154,14 +148,16 @@
 
   /* istanbul ignore else */
   if (typeof module === 'object' && typeof module.exports === 'object') {
-    module.exports = f(require('ramda'), require('sanctuary-def'));
+    module.exports = f(require('ramda'),
+                       require('sanctuary-type-classes'),
+                       require('sanctuary-def'));
   } else if (typeof define === 'function' && define.amd != null) {
-    define(['ramda', 'sanctuary-def'], f);
+    define(['ramda', 'sanctuary-type-classes', 'sanctuary-def'], f);
   } else {
-    self.sanctuary = f(self.R, self.sanctuaryDef);
+    self.sanctuary = f(self.R, self.sanctuaryTypeClasses, self.sanctuaryDef);
   }
 
-}(function(R, $) {
+}(function(R, λ, $) {
 
   'use strict';
 
@@ -221,71 +217,29 @@
   var negativeZero = R.either(R.equals(-0), R.equals(new Number(-0)));
 
   //  Accessible :: TypeClass
-  var Accessible = $.TypeClass(
+  var Accessible = λ.TypeClass(
     'sanctuary/Accessible',
+    [],
     function(x) { return x != null; }
   );
 
-  //  Applicative :: TypeClass
-  var Applicative = $.TypeClass(
-    'sanctuary/Applicative',
-    function(x) {
-      return _type(x) === 'Array' ||
-             Apply._test(x) && (hasMethod(OF)(x) ||
-                                hasMethod(OF)(x.constructor));
-    }
-  );
-
-  //  Apply :: TypeClass
-  var Apply = $.TypeClass(
-    'sanctuary/Apply',
-    function(x) {
-      return R.contains(_type(x), ['Array', 'Function']) ||
-             Functor._test(x) && hasMethod(AP)(x);
-    }
-  );
-
-  //  Foldable :: TypeClass
-  var Foldable = $.TypeClass(
-    'sanctuary/Foldable',
-    function(x) {
-      return _type(x) === 'Array' || hasMethod(REDUCE)(x);
-    }
-  );
-
-  //  Functor :: TypeClass
-  var Functor = $.TypeClass(
-    'sanctuary/Functor',
-    function(x) {
-      return R.contains(_type(x), ['Array', 'Function']) ||
-             hasMethod(MAP)(x);
-    }
-  );
-
   //  Monoid :: TypeClass
-  var Monoid = $.TypeClass(
+  var Monoid = λ.TypeClass(
     'sanctuary/Monoid',
+    [],
     function(x) {
       return R.contains(_type(x), ['Array', 'Boolean', 'Object', 'String']) ||
-             hasMethod(EMPTY)(x);
+             hasMethod('empty')(x);
     }
   );
 
   //  Ord :: TypeClass
-  var Ord = $.TypeClass(
+  var Ord = λ.TypeClass(
     'sanctuary/Ord',
+    [],
     R.anyPass([$.String._test, $.ValidDate._test, $.ValidNumber._test])
   );
 
-  //  Semigroup :: TypeClass
-  var Semigroup = $.TypeClass(
-    'sanctuary/Semigroup',
-    function(x) {
-      return R.contains(_type(x), ['Array', 'String']) ||
-             hasMethod(CONCAT)(x);
-    }
-  );
-
   var a = $.TypeVariable('a');
   var b = $.TypeVariable('b');
   var c = $.TypeVariable('c');
@@ -509,6 +463,195 @@
         );
       });
 
+  //. ### Fantasy Land
+
+  //# concat :: Semigroup a => a -> a -> a
+  //.
+  //. Concatenates two (homogeneous) arrays, two strings, or two values of any
+  //. other type which satisfies the [Semigroup][] specification.
+  //.
+  //. ```javascript
+  //. > S.concat([1, 2, 3], [4, 5, 6])
+  //. [1, 2, 3, 4, 5, 6]
+  //.
+  //. > S.concat('foo', 'bar')
+  //. 'foobar'
+  //.
+  //. > S.concat(S.Just('foo'), S.Just('bar'))
+  //. S.Just('foobar')
+  //. ```
+  var concat = S.concat =
+  def('concat',
+      {a: [λ.Semigroup]},
+      [a, a, a],
+      λ.concat);
+
+  //# empty :: Monoid a => a -> a
+  //.
+  //. TK.
+  //.
+  //. ```javascript
+  //. > S.empty([1, 2, 3])
+  //. []
+  //.
+  //. > S.empty({x: 1, y: 2})
+  //. {}
+  //.
+  //. > S.empty('abc')
+  //. ''
+  //.
+  //. > S.empty(S.Just(42))
+  //. Nothing
+  //. ```
+  S.empty =
+  def('empty',
+      {a: [Monoid]},
+      [a, a],
+      λ.empty);
+
+  //# map :: Functor f => (a -> b) -> f a -> f b
+  //.
+  //. TK.
+  //.
+  //. ```javascript
+  //. > S.map(S.inc, [1, 2, 3])
+  //. [2, 3, 4]
+  //.
+  //. > S.map(S.inc, {x: 1, y: 2})
+  //. {x: 2, y: 3}
+  //.
+  //. > S.map(S.inc, R.length)([1, 2, 3])
+  //. 4
+  //.
+  //. > S.map(S.inc, S.Just(42))
+  //. Just(43)
+  //.
+  //. > S.map(S.inc, S.Right(42))
+  //. Right(43)
+  //. ```
+  var map = S.map =
+  def('map',
+      {a: [λ.Functor], b: [λ.Functor]},
+      [$.AnyFunction, a, b],
+      λ.map);
+
+  //# reduce :: Foldable f => (a -> b -> a) -> a -> f b -> a
+  //.
+  //. Takes a curried binary function, an initial value, and a [Foldable][],
+  //. and applies the function to the initial value and the Foldable's first
+  //. value, then applies the function to the result of the previous
+  //. application and the Foldable's second value. Repeats this process
+  //. until each of the Foldable's values has been used. Returns the initial
+  //. value if the Foldable is empty; the result of the final application
+  //. otherwise.
+  //.
+  //. See also [`reduce_`](#reduce_).
+  //.
+  //. ```javascript
+  //. > S.reduce(S.add, 0, [1, 2, 3, 4, 5])
+  //. 15
+  //.
+  //. > S.reduce(xs => x => [x].concat(xs), [], [1, 2, 3, 4, 5])
+  //. [5, 4, 3, 2, 1]
+  //. ```
+  var reduce = S.reduce =
+  def('reduce',
+      {b: [λ.Foldable]},
+      [$.AnyFunction, a, b, a],
+      function(f_, initial, foldable) {
+        var f = function(a, b) {
+          return f_(a)(b);
+        };
+        return reduce_(f, initial, foldable);
+      });
+
+  //# reduce_ :: Foldable f => ((a, b) -> a) -> a -> f b -> a
+  //.
+  //. Version of [`reduce`](#reduce) accepting uncurried functions.
+  var reduce_ = S.reduce_ =
+  def('reduce_',
+      {b: [λ.Foldable]},
+      [$.AnyFunction, a, b, a],
+      λ.reduce);
+
+  //# sequence :: (Applicative f, Traversable t) => (a -> f a) -> t (f a) -> f (t a)
+  //.
+  //. TK.
+  //.
+  //. ```javascript
+  //. > S.sequence(S.Maybe.of, [S.Just(1), S.Just(2), S.Just(3)])
+  //. Just([1, 2, 3])
+  //.
+  //. > S.sequence(S.Maybe.of, [S.Just(1), S.Just(2), S.Nothing])
+  //. Nothing
+  //.
+  //. > S.sequence(R.of, S.Just([1, 2, 3]))
+  //. [Just(1), Just(2), Just(3)]
+  //.
+  //. > S.sequence(R.of, S.Nothing)
+  //. [Nothing]
+  //. ```
+  S.sequence =
+  def('sequence',
+      {a: [λ.Traversable], b: [λ.Applicative]},
+      [$.AnyFunction, a, b],
+      λ.sequence);
+
+  //# ap :: Apply f => f (a -> b) -> f a -> f b
+  //.
+  //. TK.
+  //.
+  //. ```javascript
+  //. > S.ap([Math.sqrt, S.inc], [1, 4, 9, 16, 25])
+  //. [1, 2, 3, 4, 5, 2, 5, 10, 17, 26]
+  //.
+  //. > S.ap(x => n => R.repeat(x, n), R.length)('abc')
+  //. ['abc', 'abc', 'abc']
+  //.
+  //. > S.ap(S.Just(S.inc), S.Just(42))
+  //. S.Just(43)
+  //. ```
+  var ap = S.ap =
+  def('ap',
+      {a: [λ.Apply], b: [λ.Apply], f: [λ.Apply]},
+      [a, b, c],
+      λ.ap);
+
+  //# chain :: Chain f => (a -> f b) -> f a -> f b
+  //.
+  //. TK.
+  //.
+  //. ```javascript
+  //. > S.chain(x => [x, x], [1, 2, 3])
+  //. [1, 1, 2, 2, 3, 3]
+  //.
+  //. > S.chain(S.parseInt(10), S.Just('42'))
+  //. Just(42)
+  //. ```
+  var chain = S.chain =
+  def('chain',
+      {a: [λ.Chain], b: [λ.Chain]},
+      [$.AnyFunction, a, b],
+      λ.chain);
+
+  //# extend :: Extend e => (e a -> a) -> e a -> e a
+  //.
+  //. TK.
+  S.extend =
+  def('extend',
+      {a: [λ.Extend], b: [λ.Extend]},
+      [a, b, b],
+      λ.extend);
+
+  //# extract :: Extend e => e a -> a
+  //.
+  //. TK.
+  S.extract =
+  def('extract',
+      {a: [λ.Extend]},
+      [a, b],
+      λ.extract);
+
   //. ### Combinator
 
   //# I :: a -> a
@@ -535,7 +678,7 @@
   //. > S.K('foo', 'bar')
   //. 'foo'
   //.
-  //. > R.map(S.K(42), R.range(0, 5))
+  //. > S.map(S.K(42), R.range(0, 5))
   //. [42, 42, 42, 42, 42]
   //. ```
   S.K =
@@ -554,13 +697,13 @@
   //. > S.A(S.inc, 42)
   //. 43
   //.
-  //. > R.map(S.A(R.__, 100), [S.inc, Math.sqrt])
+  //. > S.map(S.A(R.__, 100), [S.inc, Math.sqrt])
   //. [101, 10]
   //. ```
   S.A =
   def('A',
       {},
-      [$.Function, a, b],
+      [$.AnyFunction, a, b],
       function(f, x) { return f(x); });
 
   //# T :: a -> (a -> b) -> b
@@ -579,7 +722,7 @@
   S.T =
   def('T',
       {},
-      [a, $.Function, b],
+      [a, $.AnyFunction, b],
       function(x, f) { return f(x); });
 
   //# C :: (a -> b -> c) -> b -> a -> c
@@ -602,7 +745,7 @@
   S.C =
   def('C',
       {},
-      [$.Function, b, a, c],
+      [$.AnyFunction, b, a, c],
       function(f, x, y) { return f(y)(x); });
 
   //# B :: (b -> c) -> (a -> b) -> a -> c
@@ -619,7 +762,7 @@
   S.B =
   def('B',
       {},
-      [$.Function, $.Function, a, c],
+      [$.AnyFunction, $.AnyFunction, a, c],
       compose3);
 
   //# S :: (a -> b -> c) -> (a -> b) -> a -> c
@@ -637,7 +780,7 @@
   S.S =
   def('S',
       {},
-      [$.Function, $.Function, a, c],
+      [$.AnyFunction, $.AnyFunction, a, c],
       function(f, g, x) { return f(x)(g(x)); });
 
   //. ### Function
@@ -650,13 +793,13 @@
   //. See also [`C`](#C).
   //.
   //. ```javascript
-  //. > R.map(S.flip(Math.pow)(2), [1, 2, 3, 4, 5])
+  //. > S.map(S.flip(Math.pow)(2), [1, 2, 3, 4, 5])
   //. [1, 4, 9, 16, 25]
   //. ```
   S.flip =
   def('flip',
       {},
-      [$.Function, b, a, c],
+      [$.AnyFunction, b, a, c],
       function(f, x, y) { return f(y, x); });
 
   //# lift :: Functor f => (a -> b) -> f a -> f b
@@ -672,9 +815,9 @@
   //. ```
   S.lift =
   def('lift',
-      {a: [Functor], b: [Functor]},
-      [$.Function, a, b],
-      R.map);
+      {a: [λ.Functor], b: [λ.Functor]},
+      [$.AnyFunction, a, b],
+      map);
 
   //# lift2 :: Apply f => (a -> b -> c) -> f a -> f b -> f c
   //.
@@ -696,9 +839,9 @@
   //. ```
   S.lift2 =
   def('lift2',
-      {a: [Apply], b: [Apply], c: [Apply]},
-      [$.Function, a, b, c],
-      function(f, x, y) { return R.ap(R.map(f, x), y); });
+      {a: [λ.Apply], b: [λ.Apply], c: [λ.Apply]},
+      [$.AnyFunction, a, b, c],
+      function(f, x, y) { return ap(map(f, x), y); });
 
   //# lift3 :: Apply f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
   //.
@@ -714,9 +857,9 @@
   //. ```
   S.lift3 =
   def('lift3',
-      {a: [Apply], b: [Apply], c: [Apply], d: [Apply]},
-      [$.Function, a, b, c, d],
-      function(f, x, y, z) { return R.ap(R.ap(R.map(f, x), y), z); });
+      {a: [λ.Apply], b: [λ.Apply], c: [λ.Apply], d: [λ.Apply]},
+      [$.AnyFunction, a, b, c, d],
+      function(f, x, y, z) { return ap(ap(map(f, x), y), z); });
 
   //. ### Composition
 
@@ -738,7 +881,7 @@
   var compose = S.compose =
   def('compose',
       {},
-      [$.Function, $.Function, a, c],
+      [$.AnyFunction, $.AnyFunction, a, c],
       compose3);
 
   //# pipe :: [(a -> b), (b -> c), ..., (m -> n)] -> a -> n
@@ -759,7 +902,7 @@
   S.pipe =
   def('pipe',
       {},
-      [$.Array($.Function), a, b],
+      [$.Array($.AnyFunction), a, b],
       function(fs, x) { return R.reduceRight(compose2, I, fs)(x); });
 
   //# meld :: [** -> *] -> (* -> * -> ... -> *)
@@ -791,9 +934,9 @@
   S.meld =
   def('meld',
       {},
-      [$.Array($.Function), $.Function],
+      [$.Array($.AnyFunction), $.AnyFunction],
       function(fs) {
-        var n = 1 + sum(R.map(R.length, fs)) - fs.length;
+        var n = 1 + sum(map(R.length, fs)) - fs.length;
         return R.curryN(n, function() {
           var args = Array.prototype.slice.call(arguments);
           for (var idx = 0; idx < fs.length; idx += 1) {
@@ -905,7 +1048,7 @@
   Maybe.prototype[AP] =
   method('Maybe#ap',
          {},
-         [$Maybe($.Function), $Maybe(a), $Maybe(b)],
+         [$Maybe($.AnyFunction), $Maybe(a), $Maybe(b)],
          function(mf, mx) { return mf.isJust ? mx.map(mf.value) : mf; });
 
   //# Maybe#chain :: Maybe a ~> (a -> Maybe b) -> Maybe b
@@ -927,7 +1070,7 @@
   Maybe.prototype[CHAIN] =
   method('Maybe#chain',
          {},
-         [$Maybe(a), $.Function, $Maybe(b)],
+         [$Maybe(a), $.AnyFunction, $Maybe(b)],
          function(maybe, f) { return maybe.isJust ? f(maybe.value) : maybe; });
 
   //# Maybe#concat :: Semigroup a => Maybe a ~> Maybe a -> Maybe a
@@ -961,7 +1104,7 @@
   Maybe.prototype.concat =
   Maybe.prototype[CONCAT] =
   method('Maybe#concat',
-         {a: [Semigroup]},
+         {a: [λ.Semigroup]},
          [$Maybe(a), $Maybe(a), $Maybe(a)],
          function(mx, my) {
            return mx.isNothing ? my :
@@ -1036,7 +1179,7 @@
   Maybe.prototype[EXTEND] =
   method('Maybe#extend',
          {},
-         [$Maybe(a), $.Function, $Maybe(a)],
+         [$Maybe(a), $.AnyFunction, $Maybe(a)],
          function(maybe, f) { return maybe.isJust ? Just(f(maybe)) : maybe; });
 
   //# Maybe#filter :: Maybe a ~> (a -> Boolean) -> Maybe a
@@ -1054,7 +1197,7 @@
   Maybe.prototype.filter =
   method('Maybe#filter',
          {},
-         [$Maybe(a), $.Function, $Maybe(a)],
+         [$Maybe(a), $.AnyFunction, $Maybe(a)],
          function(maybe, pred) { return filter(pred, maybe); });
 
   //# Maybe#map :: Maybe a ~> (a -> b) -> Maybe b
@@ -1074,7 +1217,7 @@
   Maybe.prototype[MAP] =
   method('Maybe#map',
          {},
-         [$Maybe(a), $.Function, $Maybe(b)],
+         [$Maybe(a), $.AnyFunction, $Maybe(b)],
          function(maybe, f) {
            return maybe.isJust ? Just(f(maybe.value)) : maybe;
          });
@@ -1114,7 +1257,7 @@
   Maybe.prototype[REDUCE] =
   method('Maybe#reduce',
          {},
-         [$Maybe(a), $.Function, b, b],
+         [$Maybe(a), $.AnyFunction, b, b],
          function(maybe, f, x) {
            return maybe.isJust ? f(x, maybe.value) : x;
          });
@@ -1140,14 +1283,10 @@
   Maybe.prototype.sequence =
   Maybe.prototype[SEQUENCE] =
   method('Maybe#sequence',
-         {a: [Applicative], b: [Applicative]},
-         [$Maybe(a), $.Function, b],
+         {a: [λ.Applicative], b: [λ.Applicative]},
+         [$Maybe(a), $.AnyFunction, b],
          function(maybe, of) {
-           return maybe.isNothing ?
-             of(maybe) :
-             maybe.value != null && typeof maybe.value[MAP] === 'function' ?
-               maybe.value[MAP](Just) :
-               R.map(Just, maybe.value);
+           return maybe.isJust ? map(Just, maybe.value) : of(maybe);
          });
 
   //# Maybe#toBoolean :: Maybe a ~> Boolean
@@ -1331,7 +1470,7 @@
   var maybe = S.maybe =
   def('maybe',
       {},
-      [b, $.Function, $Maybe(a), b],
+      [b, $.AnyFunction, $Maybe(a), b],
       function(x, f, maybe) { return fromMaybe(x, maybe.map(f)); });
 
   //# justs :: Array (Maybe a) -> Array a
@@ -1349,7 +1488,7 @@
   def('justs',
       {},
       [$.Array($Maybe(a)), $.Array(a)],
-      R.chain(maybe([], R.of)));
+      chain(maybe([], R.of)));
 
   //# mapMaybe :: (a -> Maybe b) -> Array a -> Array b
   //.
@@ -1368,8 +1507,8 @@
   S.mapMaybe =
   def('mapMaybe',
       {},
-      [$.Function, $.Array(a), $.Array(b)],
-      function(f, xs) { return justs(R.map(f, xs)); });
+      [$.AnyFunction, $.Array(a), $.Array(b)],
+      function(f, xs) { return justs(map(f, xs)); });
 
   //# encase :: (a -> b) -> a -> Maybe b
   //.
@@ -1390,7 +1529,7 @@
   var encase = S.encase =
   def('encase',
       {},
-      [$.Function, a, $Maybe(b)],
+      [$.AnyFunction, a, $Maybe(b)],
       function(f, x) {
         try {
           return Just(f(x));
@@ -1407,7 +1546,7 @@
   var encase2 = S.encase2 =
   def('encase2',
       {},
-      [$.Function, a, b, $Maybe(c)],
+      [$.AnyFunction, a, b, $Maybe(c)],
       function(f, x, y) {
         try {
           return Just(f(x)(y));
@@ -1422,7 +1561,7 @@
   S.encase2_ =
   def('encase2_',
       {},
-      [$.Function, a, b, $Maybe(c)],
+      [$.AnyFunction, a, b, $Maybe(c)],
       function(f_, x, y) {
         var f = function(x) {
           return function(y) {
@@ -1440,7 +1579,7 @@
   var encase3 = S.encase3 =
   def('encase3',
       {},
-      [$.Function, a, b, c, $Maybe(d)],
+      [$.AnyFunction, a, b, c, $Maybe(d)],
       function(f, x, y, z) {
         try {
           return Just(f(x)(y)(z));
@@ -1455,7 +1594,7 @@
   S.encase3_ =
   def('encase3_',
       {},
-      [$.Function, a, b, c, $Maybe(d)],
+      [$.AnyFunction, a, b, c, $Maybe(d)],
       function(f_, x, y, z) {
         var f = function(x) {
           return function(y) {
@@ -1576,7 +1715,7 @@
   Either.prototype[AP] =
   method('Either#ap',
          {},
-         [$Either(a, $.Function), $Either(a, b), $Either(a, c)],
+         [$Either(a, $.AnyFunction), $Either(a, b), $Either(a, c)],
          function(ef, ex) { return ef.isRight ? ex.map(ef.value) : ef; });
 
   //# Either#chain :: Either a b ~> (b -> Either a c) -> Either a c
@@ -1603,7 +1742,7 @@
   Either.prototype[CHAIN] =
   method('Either#chain',
          {},
-         [$Either(a, b), $.Function, $Either(a, c)],
+         [$Either(a, b), $.AnyFunction, $Either(a, c)],
          function(either, f) {
            return either.isRight ? f(either.value) : either;
          });
@@ -1640,7 +1779,7 @@
   Either.prototype.concat =
   Either.prototype[CONCAT] =
   method('Either#concat',
-         {a: [Semigroup], b: [Semigroup]},
+         {a: [λ.Semigroup], b: [λ.Semigroup]},
          [$Either(a, b), $Either(a, b), $Either(a, b)],
          function(ex, ey) {
            return ex.isLeft === ey.isLeft ?
@@ -1695,7 +1834,7 @@
   Either.prototype[EXTEND] =
   method('Either#extend',
          {},
-         [$Either(a, b), $.Function, $Either(a, b)],
+         [$Either(a, b), $.AnyFunction, $Either(a, b)],
          function(either, f) {
            return either.isLeft ? either : Right(f(either));
          });
@@ -1717,7 +1856,7 @@
   Either.prototype[MAP] =
   method('Either#map',
          {},
-         [$Either(a, b), $.Function, $Either(a, c)],
+         [$Either(a, b), $.AnyFunction, $Either(a, c)],
          function(either, f) {
            return either.isRight ? Right(f(either.value)) : either;
          });
@@ -1757,7 +1896,7 @@
   Either.prototype[REDUCE] =
   method('Either#reduce',
          {},
-         [$Either(a, b), $.Function, c, c],
+         [$Either(a, b), $.AnyFunction, c, c],
          function(either, f, x) {
            return either.isRight ? f(x, either.value) : x;
          });
@@ -1784,14 +1923,10 @@
   Either.prototype.sequence =
   Either.prototype[SEQUENCE] =
   method('Either#sequence',
-         {b: [Applicative], c: [Applicative]},
-         [$Either(a, b), $.Function, c],
+         {b: [λ.Applicative], c: [λ.Applicative]},
+         [$Either(a, b), $.AnyFunction, c],
          function(either, of) {
-           return either.isLeft ?
-             of(either) :
-             either.value != null && typeof either.value[MAP] === 'function' ?
-               either.value[MAP](Right) :
-               R.map(Right, either.value);
+           return either.isRight ? map(Right, either.value) : of(either);
          });
 
   //# Either#toBoolean :: Either a b ~> Boolean
@@ -1973,7 +2108,7 @@
   S.either =
   def('either',
       {},
-      [$.Function, $.Function, $Either(a, b), c],
+      [$.AnyFunction, $.AnyFunction, $Either(a, b), c],
       function(l, r, either) {
         return either.isLeft ? l(either.value) : r(either.value);
       });
@@ -1993,7 +2128,7 @@
   def('lefts',
       {},
       [$.Array($Either(a, b)), $.Array(a)],
-      R.chain(function(either) {
+      chain(function(either) {
         return either.isLeft ? [either.value] : [];
       }));
 
@@ -2012,7 +2147,7 @@
   def('rights',
       {},
       [$.Array($Either(a, b)), $.Array(b)],
-      R.chain(function(either) {
+      chain(function(either) {
         return either.isRight ? [either.value] : [];
       }));
 
@@ -2039,7 +2174,7 @@
   S.encaseEither =
   def('encaseEither',
       {},
-      [$.Function, $.Function, a, $Either(l, r)],
+      [$.AnyFunction, $.AnyFunction, a, $Either(l, r)],
       function(f, g, x) {
         try {
           return Right(g(x));
@@ -2056,7 +2191,7 @@
   var encaseEither2 = S.encaseEither2 =
   def('encaseEither2',
       {},
-      [$.Function, $.Function, a, b, $Either(l, r)],
+      [$.AnyFunction, $.AnyFunction, a, b, $Either(l, r)],
       function(f, g, x, y) {
         try {
           return Right(g(x)(y));
@@ -2072,7 +2207,7 @@
   S.encaseEither2_ =
   def('encaseEither2_',
       {},
-      [$.Function, $.Function, a, b, $Either(l, r)],
+      [$.AnyFunction, $.AnyFunction, a, b, $Either(l, r)],
       function(f, g_, x, y) {
         var g = function(x) {
           return function(y) {
@@ -2090,7 +2225,7 @@
   var encaseEither3 = S.encaseEither3 =
   def('encaseEither3',
       {},
-      [$.Function, $.Function, a, b, c, $Either(l, r)],
+      [$.AnyFunction, $.AnyFunction, a, b, c, $Either(l, r)],
       function(f, g, x, y, z) {
         try {
           return Right(g(x)(y)(z));
@@ -2106,7 +2241,7 @@
   S.encaseEither3_ =
   def('encaseEither3',
       {},
-      [$.Function, $.Function, a, b, c, $Either(l, r)],
+      [$.AnyFunction, $.AnyFunction, a, b, c, $Either(l, r)],
       function(f, g_, x, y, z) {
         var g = function(x) {
           return function(y) {
@@ -2143,8 +2278,9 @@
   //. ### Alternative
 
   //  Alternative :: TypeClass
-  var Alternative = $.TypeClass(
+  var Alternative = λ.TypeClass(
     'Alternative',
+    [],
     function(x) {
       return R.contains(R.type(x), ['Array', 'Boolean']) ||
              hasMethod('toBoolean')(x);
@@ -2272,7 +2408,7 @@
   S.ifElse =
   def('ifElse',
       {},
-      [$.Function, $.Function, $.Function, a, b],
+      [$.AnyFunction, $.AnyFunction, $.AnyFunction, a, b],
       function(pred, f, g, x) { return pred(x) ? f(x) : g(x); });
 
   //# allPass :: Array (a -> Boolean) -> a -> Boolean
@@ -2292,7 +2428,7 @@
   S.allPass =
   def('allPass',
       {},
-      [$.Array($.Function), a, $.Boolean],
+      [$.Array($.AnyFunction), a, $.Boolean],
       function(preds, x) {
         for (var idx = 0; idx < preds.length; idx += 1) {
           if (!preds[idx](x)) return false;
@@ -2317,7 +2453,7 @@
   S.anyPass =
   def('anyPass',
       {},
-      [$.Array($.Function), a, $.Boolean],
+      [$.Array($.AnyFunction), a, $.Boolean],
       function(preds, x) {
         for (var idx = 0; idx < preds.length; idx += 1) {
           if (preds[idx](x)) return true;
@@ -2333,30 +2469,6 @@
   //.
   //. `[a]` is the notation used to represent a List of values of type `a`.
 
-  //# concat :: Semigroup a => a -> a -> a
-  //.
-  //. Concatenates two (homogeneous) arrays, two strings, or two values of any
-  //. other type which satisfies the [Semigroup][] specification.
-  //.
-  //. ```javascript
-  //. > S.concat([1, 2, 3], [4, 5, 6])
-  //. [1, 2, 3, 4, 5, 6]
-  //.
-  //. > S.concat('foo', 'bar')
-  //. 'foobar'
-  //.
-  //. > S.concat(S.Just('foo'), S.Just('bar'))
-  //. S.Just('foobar')
-  //. ```
-  var concat = S.concat =
-  def('concat',
-      {a: [Semigroup]},
-      [a, a, a],
-      function(x, y) {
-        return R.contains(R.type(x), ['Array', 'String']) ? x.concat(y)
-                                                          : x[CONCAT](y);
-      });
-
   //# slice :: Integer -> Integer -> [a] -> Maybe [a]
   //.
   //. Returns Just a list containing the elements from the supplied list
@@ -2420,7 +2532,7 @@
       {},
       [$.Integer, List(a), $Maybe(a)],
       function(n, xs) {
-        return R.map(R.head, slice(n, n === -1 ? -0 : n + 1, xs));
+        return map(R.head, slice(n, n === -1 ? -0 : n + 1, xs));
       });
 
   //# head :: [a] -> Maybe a
@@ -2620,8 +2732,9 @@
       });
 
   //  ArrayLike :: TypeClass
-  var ArrayLike = $.TypeClass(
+  var ArrayLike = λ.TypeClass(
     'ArrayLike',
+    [],
     function(x) {
       return x != null &&
              typeof x !== 'function' &&
@@ -2739,7 +2852,7 @@
   S.find =
   def('find',
       {},
-      [$.Function, $.Array(a), $Maybe(a)],
+      [$.AnyFunction, $.Array(a), $Maybe(a)],
       function(pred, xs) {
         for (var idx = 0, len = xs.length; idx < len; idx += 1) {
           if (pred(xs[idx])) {
@@ -2767,56 +2880,7 @@
   def('pluck',
       {a: [Accessible]},
       [TypeRep, $.String, $.Array(a), $.Array($Maybe(b))],
-      function(type, key, xs) { return R.map(get(type, key), xs); });
-
-  //# reduce :: Foldable f => (a -> b -> a) -> a -> f b -> a
-  //.
-  //. Takes a curried binary function, an initial value, and a [Foldable][],
-  //. and applies the function to the initial value and the Foldable's first
-  //. value, then applies the function to the result of the previous
-  //. application and the Foldable's second value. Repeats this process
-  //. until each of the Foldable's values has been used. Returns the initial
-  //. value if the Foldable is empty; the result of the final application
-  //. otherwise.
-  //.
-  //. See also [`reduce_`](#reduce_).
-  //.
-  //. ```javascript
-  //. > S.reduce(S.add, 0, [1, 2, 3, 4, 5])
-  //. 15
-  //.
-  //. > S.reduce(xs => x => [x].concat(xs), [], [1, 2, 3, 4, 5])
-  //. [5, 4, 3, 2, 1]
-  //. ```
-  var reduce = S.reduce =
-  def('reduce',
-      {b: [Foldable]},
-      [$.Function, a, b, a],
-      function(f_, initial, foldable) {
-        var f = function(a, b) {
-          return f_(a)(b);
-        };
-        return reduce_(f, initial, foldable);
-      });
-
-  //# reduce_ :: Foldable f => ((a, b) -> a) -> a -> f b -> a
-  //.
-  //. Version of [`reduce`](#reduce) accepting uncurried functions.
-  var reduce_ = S.reduce_ =
-  def('reduce_',
-      {b: [Foldable]},
-      [$.Function, a, b, a],
-      function(f, initial, foldable) {
-        if (_type(foldable) === 'Array') {
-          var acc = initial;
-          for (var idx = 0; idx < foldable.length; idx += 1) {
-            acc = f(acc, foldable[idx]);
-          }
-          return acc;
-        } else {
-          return foldable[REDUCE](f, initial);
-        }
-      });
+      function(type, key, xs) { return map(get(type, key), xs); });
 
   //# unfoldr :: (b -> Maybe (Pair a b)) -> b -> Array a
   //.
@@ -2837,7 +2901,7 @@
   S.unfoldr =
   def('unfoldr',
       {},
-      [$.Function, b, $.Array(a)],
+      [$.AnyFunction, b, $.Array(a)],
       function(f, x) {
         var result = [];
         var m = f(x);
@@ -3048,7 +3112,7 @@
   //. ```
   var sum = S.sum =
   def('sum',
-      {f: [Foldable]},
+      {f: [λ.Foldable]},
       [f, $.FiniteNumber],
       reduce(function(a) { return function(b) { return a + b; }; }, 0));
 
@@ -3127,7 +3191,7 @@
   //. ```
   S.product =
   def('product',
-      {f: [Foldable]},
+      {f: [λ.Foldable]},
       [f, $.FiniteNumber],
       reduce(function(a) { return function(b) { return a * b; }; }, 1));
 
@@ -3165,7 +3229,7 @@
   //. ```
   S.mean =
   def('mean',
-      {f: [Foldable]},
+      {f: [λ.Foldable]},
       [f, $Maybe($.FiniteNumber)],
       function(foldable) {
         var result = reduce_(
@@ -3342,7 +3406,7 @@
   def('parseFloat',
       {},
       [$.String, $Maybe($.Number)],
-      R.pipe(Just, R.filter(validFloatRepr), R.map(parseFloat)));
+      R.pipe(Just, R.filter(validFloatRepr), map(parseFloat)));
 
   //# parseInt :: Integer -> String -> Maybe Integer
   //.
@@ -3384,7 +3448,7 @@
                           R.all(R.pipe(toUpper,
                                        R.indexOf(_, charset),
                                        R.gte(_, 0))))),
-          R.map(R.partialRight(parseInt, [radix])),
+          map(R.partialRight(parseInt, [radix])),
           R.filter($.Integer._test)
         )(s);
       });
@@ -3490,7 +3554,7 @@
       [$.RegExp, $.String, $Maybe($.Array($Maybe($.String)))],
       function(pattern, s) {
         var match = s.match(pattern);
-        return match == null ? Nothing : Just(R.map(toMaybe, match));
+        return match == null ? Nothing : Just(λ.map(toMaybe, match));
       });
 
   //. ### String
@@ -3608,7 +3672,7 @@
   def('unlines',
       {},
       [$.Array($.String), $.String],
-      compose(R.join(''), R.map(concat(_, '\n'))));
+      compose(R.join(''), map(concat(_, '\n'))));
 
   return S;
 
@@ -3631,7 +3695,6 @@
 //. [Monoid]:         https://github.com/fantasyland/fantasy-land#monoid
 //. [Nullable]:       https://github.com/sanctuary-js/sanctuary-def#nullable
 //. [R.equals]:       http://ramdajs.com/docs/#equals
-//. [R.map]:          http://ramdajs.com/docs/#map
 //. [R.type]:         http://ramdajs.com/docs/#type
 //. [Ramda]:          http://ramdajs.com/
 //. [RegExp]:         https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp
diff --git a/package.json b/package.json
index bd4b4ffe..e40cdefc 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,8 @@
   },
   "dependencies": {
     "ramda": "0.22.x",
-    "sanctuary-def": "0.6.x"
+    "sanctuary-def": "sanctuary-js/sanctuary-def#dc-sanctuary-type-classes",
+    "sanctuary-type-classes": "sanctuary-js/sanctuary-type-classes#dc-everything"
   },
   "devDependencies": {
     "doctest": "0.10.x",
diff --git a/test/Either/Either.js b/test/Either/Either.js
index 5e91f170..5d432012 100644
--- a/test/Either/Either.js
+++ b/test/Either/Either.js
@@ -19,7 +19,7 @@ var SEQUENCE    = FantasyLand.sequence;
 
 //  Identity :: a -> Identity a
 var Identity = function Identity(x) {
-  var $ = {value: x};
+  var $ = {value: x, toString: R.always('Identity(' + R.toString(x) + ')')};
   $[OF] = Identity;
   $[MAP] = function(fn) { return Identity(fn(x)); };
   $[AP] = function(y) { return Identity(x(y)); };
diff --git a/test/I.js b/test/I.js
index 6369407e..c99b4f9f 100644
--- a/test/I.js
+++ b/test/I.js
@@ -14,8 +14,6 @@ describe('I', function() {
   it('returns its argument', function() {
     eq(S.I([1, 2, 3]), [1, 2, 3]);
     eq(S.I(['foo', 42]), ['foo', 42]);
-    eq(S.I({'@@type': 'my-package/Foreign'}),
-       {'@@type': 'my-package/Foreign'});
   });
 
 });
diff --git a/test/Maybe/Maybe.js b/test/Maybe/Maybe.js
index 3af60ba0..a6aaba97 100644
--- a/test/Maybe/Maybe.js
+++ b/test/Maybe/Maybe.js
@@ -19,7 +19,7 @@ var SEQUENCE    = FantasyLand.sequence;
 
 //  Identity :: a -> Identity a
 var Identity = function Identity(x) {
-  var $ = {value: x};
+  var $ = {value: x, toString: R.always('Identity(' + R.toString(x) + ')')};
   $[OF] = Identity;
   $[MAP] = function(fn) { return Identity(fn(x)); };
   $[AP] = function(y) { return Identity(x(y)); };
diff --git a/test/map.js b/test/map.js
new file mode 100644
index 00000000..67cae972
--- /dev/null
+++ b/test/map.js
@@ -0,0 +1,73 @@
+'use strict';
+
+var throws = require('assert').throws;
+
+var eq = require('./utils').eq;
+var errorEq = require('./utils').errorEq;
+var S = require('..');
+
+
+describe('map', function() {
+
+  it('is a binary function', function() {
+    eq(typeof S.map, 'function');
+    eq(S.map.length, 2);
+  });
+
+  it('type checks its arguments', function() {
+    throws(function() { S.map('xxx'); },
+           errorEq(TypeError,
+                   'Invalid value\n' +
+                   '\n' +
+                   'map :: (Functor a, Functor b) => Function -> a -> b\n' +
+                   '                                 ^^^^^^^^\n' +
+                   '                                    1\n' +
+                   '\n' +
+                   '1)  "xxx" :: String\n' +
+                   '\n' +
+                   'The value at position 1 is not a member of ‘Function’.\n'));
+
+    throws(function() { S.map(S.toUpper, 'xxx'); },
+           errorEq(TypeError,
+                   'Type-class constraint violation\n' +
+                   '\n' +
+                   'map :: (Functor a, Functor b) => Function -> a -> b\n' +
+                   '        ^^^^^^^^^                            ^\n' +
+                   '                                             1\n' +
+                   '\n' +
+                   '1)  "xxx" :: String\n' +
+                   '\n' +
+                   '‘map’ requires ‘a’ to satisfy the Functor type-class constraint; the value at position 1 does not.\n'));
+  });
+
+  it('maps a function into the context of Functors', function() {
+    eq(S.map(S.not, S.odd)(2), true);
+    eq(S.map(S.not, S.odd)(3), false);
+
+    eq(S.map(S.mult(4), S.Just(2)), S.Just(8));
+    eq(S.map(S.mult(4), S.Nothing), S.Nothing);
+
+    eq(S.map(S.mult(4), S.Left(3)), S.Left(3));
+    eq(S.map(S.mult(4), S.Right(2)), S.Right(8));
+
+    eq(S.map(S.mult(2), [1, 2, 3]), [2, 4, 6]);
+    eq(S.map(S.mult(2), []), []);
+
+    eq(S.map(S.mult(2), {a: 1, b: 2, c: 3}), {a: 2, b: 4, c: 6});
+    eq(S.map(S.mult(2), {}), {});
+  });
+
+  it("does not map over an object's prototype properties", function() {
+    var Point = function Point(x, y) {
+      this.x = x;
+      this.y = y;
+    };
+
+    Point.prototype.color = 'black';
+
+    var point = new Point(0, 0);
+
+    eq(S.map(S.inc, point), {x: 1, y: 1});
+  });
+
+});