Fantasy Environment


An environment holds methods and properties.

Methods are implemented as multi-methods, which allow a form of
ad-hoc polymorphism. Duck typing is another example of ad-hoc
polymorphism, but only allows a single implementation at a time, via
prototype mutation.

A method instance is a product of a name, a predicate and an
implementation:

``javascript
var env = environment()
.method(
// Name
'negate',
// Predicate
function(n) {
return typeof n == 'number';
},
// Implementation
function(n) {
return -n;
}
);

env.negate(100) == -100;
`

We can now override the environment with Some more implementations:

`javascript
var env2 = env
.method(
'negate',
function(b) {
return typeof b == 'boolean';
},
function(b) {
return !b;
}
);

env2.negate(100) == -100;
env2.negate(true) == false;
`

Environments are immutable; references to env won't see an
implementation for boolean. The env2 environment could have
overwritten the implementation for number and code relying on env
would still work.

Properties can be accessed without dispatching on arguments. They
can almost be thought of as methods with predicates that always
return true:

`javascript
var env = fantasy.environment()
.property('name', 'Fantasy');

env.name === 'Fantasy';
`


Testing

$3

Fantasy Environment uses nodeunit
for all the tests and because of this there is currently an existing
adapter in the library to help with integration
between nodeunit and Fantasy Environment.

$3

Currently Fantasy Environment is using Istanbul
for code coverage analysis; you can run the coverage via the following
command:

_This assumes that you have istanbul installed correctly._

`
istanbul cover nodeunit -- test/*.js
``

It should report that the total coverage is at 100% (branches at 80.95%)
for the whole lib.