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:tea: minimal composable type abstraction

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# mintype [![stability][0]][1]
[![npm version][2]][3] [![build status][4]][5] [![test coverage][6]][7]
[![downloads][8]][9] [![js-standard-style][10]][11]

minimal composable type abstraction

```shell
npm install --save mintype
```

for a better type library, see [`tcomb`](https://github.com/gcanti/tcomb).

![mint tea](https://upload.wikimedia.org/wikipedia/commons/thumb/6/6c/The_menthe.jpg/495px-The_menthe.jpg)

## what?

what's a type?

**a Type `T` is a function** where

given a value `v`, `T` returns either:

- a new value `v*` (which might be `===` to `v`)
- an instance of `TypeError`

and given `v*`, `T` returns `v*`.

we can use this in many interesting ways

- create a factory `Function` that is _idempotent_, as in `F(value) === F(F(value))`
  - to do this, we throw errors in development, and ignore them in production.
- create a validation `Function` that returns `TypeError` or `null`
- create a test `Function` that returns `Boolean`
- compose many types together into one type

## example

```js
const ty = require('mintype')

const Vector = ty.compose(
  ty.Array,
  (vector) => vector.length === 2
    ? vector : new TypeError('Vector must be array of [x, y].')
  ,
  (vector) => {
    for (var i = 0; i < vector.length; i++) {
      const result = ty.validate(ty.Number, vector[i])
      if (result instanceof TypeError) return result
    }
    return vector
  }
)

const Location = ty.struct('Location', {
  position: Vector,
  velocity: Vector
})

const location = ty.create(Location, {
  position: [100, 0],
  velocity: [0, 1]
})

console.log('location', location)
// location Struct {
//   type: 'Location',
//   position: [ 100, 0 ],
//   velocity: [ 0, 1 ] }
```

## usage

### `ty = require('mintype')`

the top-level `mintype` module is a grab bag of all `mintype/*` modules.

you can also require each module separately like `require('mintype/create')`.

### `b = ty.create(T, a)`

`create(T, value)` only returns the *typed* version of `value`, as in:

- if there is an error from applying the type `T`, then `create` will throw
- otherwise `create` returns the resulting value from applying the type `T`

### `ty.validate(T, value)`

if `value` is type `T`, return `null`;

else return `TypeError` returned from `T(value)`.

### `ty.is(T, value)`

if `value` is type `T`, return `true`;

else return `false`.

### built-in types

- `ty.String`: strings
- `ty.Number`: numbers
- `ty.Integer`: integers
- `ty.Boolean`: booleans
- `ty.Array`: arrays
- `ty.Object`: plain objects
- `ty.Function`: functions
- `ty.RegExp`: regular expressions
- `ty.Date`: dates
- `ty.Nil`: `null` or `undefined`
- `ty.Any`: any value

### `ty.struct(name, propTypes)`

given a `String` (or `Symbol`) name

and an `Object` of property types corresponding to property names,

returns a `Type` that uses a constructor function for efficient data structures.

calling `Type(props)` either returns:

- the first error encountered in evaluating the props
- a `new` instance of the struct's evaluated props called on the constructor function.

note: it's possible to define methods on `Type.prototype`, which will show up as methods on any returned instances.

### `ty.compose(...Types)`

compose many types into one type, as so:

```js
const Integer = compose(
  ty.Number,
  (value) => value % 1 === 0
    ? value
    : new TypeError(`expected ${value} % 1 === 0`)
)
```

### `ty.maybe(Type)`

returns a type that can either be of type `ty.Nil` or the type passed to `ty.maybe`

## FAQ

### how to optimize types in production?

for more performant types in production, only do expensive error-checking if `process.env.NODE_ENV !== 'production'`.

this allows the code to be stripped out with [`browserify`](http://browserify.org/) bundles using [`envify`](https://github.com/hughsk/envify) and [`uglifyify`](https://github.com/hughsk/uglifyify).

the built-in types and type utilities do this already, but if you are supplying your own types from scratch you will need to do this on your own.

## examples

i built this to replace [`tcomb`](https://github.com/gcanti/tcomb) within [`inu-plays-rougelike`](https://github.com/ahdinosaur/inu-plays-roguelike) due to performance problems (and fun ideas), the integration is still a work in progress.

## inspiration

- [`tcomb`](https://github.com/gcanti/tcomb)
- @dominictarr's idea of validation as a reducer function
    (initialState, value) -> (nextState | false)
- [`stampit`](github.com/stampit-org/stampit)
- json-schema type objects
- [C data types](https://en.wikipedia.org/wiki/C_data_types#Structures)

## license

The Apache License

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

[0]: https://img.shields.io/badge/stability-experimental-orange.svg?style=flat-square
[1]: https://nodejs.org/api/documentation.html#documentation_stability_index
[2]: https://img.shields.io/npm/v/mintype.svg?style=flat-square
[3]: https://npmjs.org/package/mintype
[4]: https://img.shields.io/travis/ahdinosaur/mintype/master.svg?style=flat-square
[5]: https://travis-ci.org/ahdinosaur/mintype
[6]: https://img.shields.io/codecov/c/github/ahdinosaur/mintype/master.svg?style=flat-square
[7]: https://codecov.io/github/ahdinosaur/mintype
[8]: http://img.shields.io/npm/dm/mintype.svg?style=flat-square
[9]: https://npmjs.org/package/mintype
[10]: https://img.shields.io/badge/code%20style-standard-brightgreen.svg?style=flat-square
[11]: https://github.com/feross/standard

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