State Monad and Monad Transformer for Akh Javascript Monad Library

The StateT monad transformer adds state to a monad. The base type State provides state on its own.

``bash


To use as standalone package

$ npm install --save akh.state

To use as part of akh library

$ npm install --save akh
`

Api

StateT and State implement the Fantasy Land][fl] monad, monoid, functor, and applicative functor interfaces.

`js
// State monad
require('akh.state').State
require('akh').State

// State monad transformer
require('akh.state').StateT
require('akh').StateT
`

#### State.run(m, s), m.run(s)
Perform a stateful computation m with state s and return state, value pair.

`js
const State = require('akh.state').State

const c = State.of(1)
.chain(x => State.modify(s => s + x))
.chain(x => State.of('val'))

run(c, 's') === {'value': 'val', 'state': 's1'}
`

#### State.eval(m, s), m.eval(s)
Perform a stateful computation m with state s and return the resulting value.

`js
State.eval(c, 's') === 'val'
`

#### State.exec(m, s), m.exe(s)
Perform a stateful computation m with state s and return the resulting state.

`js
State.eval(c, 's') == 's'
`

#### StateT.run(m, s)
Same as State.run but for transformed types.

#### StateT.evalT(m, s)
Same as State.eval but for transformed types.

#### StateT.exec(m, s)
Same as State.exec but for transformed types.




State Interface

All state operations and methods are defined on both the type and its instances.

#### M.get
Get the current state.


`js
const State = require('akh.state').State

State.get.run('my state') === { value: 'my state', state: 'my state' }
`

#### M.put(s)
Set the current state to s

#### M.modify(f)
Modify the current state with f that maps the current state to a new state.




Contributing

Contributions are welcome.

To get started:

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

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