Writer Monad and Monad Transformer for Akh Javascript Monad Library

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

``bash


To use as standalone package

$ npm install --save akh.writer

To use as part of akh library

$ npm install --save akh
`

Usage

WriterT and Writer implement the [Fantasy Land][fl] monad, functor, and applicative functor interfaces.

`js
// Writer monad
require('akh.writer').Writer
require('akh').Writer

// Writer monad transformer
require('akh.writer').WriterT
require('akh').WriterT
`

#### Writer.run(m, w), m.run(w)
Perform a writer computation m without output monoid w and return { value, output}

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

#### Writer.exec(m, w), m.exec(w)
Perform a writer computation m without output monoid w and return resulting value




Writer Interface

#### Writer.tell(b)
#### WriterT(M).tell(b)
Append b to the output.

`js
Writer.of(4)
.chain(x => writer.tell(List.of('output1')).map(_ => x)))
.run(List.zero) === { value: 4, output: List of ['output1'] }
`

#### Writer.listen()
#### WriterT(M).listen()
Produces the current value output pair as { value, output }

#### m.pass()
#### t.pass()
Exec current monad which returns a [value, f], then modify current output with f and return value.


#### m.censor(f)
#### t.censor(f)
Exec current monad, then modify current output with f and return original value.




Contributing

Contributions are welcome.

To get started:

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

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