Let the fantasy begin

README.md

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+# Fantasy Land Specification
+
+(aka "Algebraic JavaScript Specification")
+
+![](logo.png)
+
+This project specifies interoperability of common algebraic
+structures:
+
+* Functor
+* Monad
+
+## General
+
+An algebra is a set of values, a set of operators that it is closed
+under and some laws it must obey.
+
+## Terminology
+
+1. "value" is any JavaScript value, including any which have the
+   structures defined below.
+
+## Algebras
+
+### Functor
+
+1. `u.map(function(a) { return a; }))` equals `u`
+2. `u.map(function(a) { return f(g(x)); })` equals `u.map(g).map(f)`
+
+#### `map` method
+
+A value which has a functor must provide a `map` method. The `map`
+method takes one argument:
+
+    u.map(f)
+
+1. `f` must be a function,
+
+    1. If `f` is not a function, the behaviour of `map` is
+       unspecified.
+    2. `f` can return any value.
+
+2. `map` must return a value of the same functor
+
+### Monad
+
+A value which satisfies the specification of a monad do not need to implement:
+
+* Functor's `map`; derivable as `function(f) { var m = this; return
+  m.then(function(a) { return m.constructor.of(f(a)); })}`
+
+1. `of(a).then(f)` equals `f(a)`
+2. `m.then(of)` equals `m`
+3. `m.then(f).then(g)` equals `m.then(function(x) { return f(x).then(g); })`
+
+#### `then` method
+
+A value which has a monad must provide a `then` method. The `then`
+method takes one argument:
+
+    m.then(f)
+
+1. `f` must be a function which returns a value
+
+    1. If `f` is not a function, the behaviour of `then` is
+       unspecified.
+    2. `f` must return a value of the same monad
+
+2. `then` must return a value of the same monad
+
+#### `constructor.of` method
+
+A value which has a monad must provide a `constructor` object. The
+`constructor` object must have an `of` method which takes one
+argument:
+
+    m.constructor.of(a)
+
+1. `of` must provide a value of the same monad
+
+    1. No parts of `a` should be checked
+
+## Notes
+
+1. It's discouraged to overload the specified methods. It can easily
+   result in broken and buggy behaviour.
+2. It is recommended to throw an exception on unspecified behaviour.
+3. An `Id` container which implements all methods is provided in
+   `id.js`.

implementations.md

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+# Conformant Implementations
+
+Here are a list of implementations of the Fantasy Land specification:
+
+* ECMAScript 5 provides a Functor for Array
+
+Conforming implementations are encouraged to promote the Fantasy Land logo:
+
+![](logo.png)