mintype

minimal composable type abstraction

npm install --save mintype

for a better type library, see tcomb.

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

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:

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 bundles using envify and 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 within inu-plays-rougelike due to performance problems (and fun ideas), the integration is still a work in progress.

inspiration

• tcomb
• @dominictarr's idea of validation as a reducer function (initialState, value) -> (nextState | false)
• stampit
• json-schema type objects
• C data types

license

The Apache License

Copyright © 2016 Michael Williams

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.