Reader Monad and Monad Transformer for Akh Javascript Monad Library

The ReaderT transformer, ReaderT, adds error control to a monad. The base type, Reader, provides error logic on its own.

``bash


To use as standalone package

$ npm install --save akh.reader

To use as part of akh library

$ npm install --save akh
`

Usage

ReaderT and Reader implement the [Fantasy Land][fl] monad, functor, and applicative functor interfaces. ReaderT is also a monoid if the underlying type is.

``js
// Reader monad
require('akh.reader').Reader
require('akh').Reader

// Reader monad transformer
require('akh.reader').ReaderT
require('akh').ReaderT
`

#### Reader.run(m, r), m.run(r)
Perform a reader computation m in environment r and return result

`js
Reader.run(
Reader.asks(r => r.a).map(x => x * 2),
{ a: 10, b: 3 }
) === 20
`

#### ReaderT.run(t), t.run()
Same as Reader.run but for a monad transformer. Returns an Reader value inside of the inner monad.




Reader Interface

#### Reader.ask
#### ReaderT(M).ask
Return the current environment.

#### Reader.asks(f)
#### ReaderT(M).asks(f)
Extract a value from the current environment using f.

#### m.local(f)
#### t.local(f)
Execute the current computation in a modified enviroment. f maps current enviroment to a new enviroment.




Contributing

Contributions are welcome.

To get started:

`bash
$ cd akh-reader
$ npm install # install dev packages
$ npm test # run tests
``

[fl]: https://github.com/fantasyland/fantasy-land