comprehension-js

List comprehension from haskell to javascript.

An easy way to build and transform array using a concise and declarative description (thanks to Haskell).

To easily understand what list comprehensions are in Haskell check out this link.

Installation

From npm

npm i comprehension-js

import { comprehensions } from 'comprehension-js';

From CDN

<script src="https://unpkg.com/comprehension-js/dist/index.min.js"></script>
<script>
var comprehensions = Comprehensions.comprehensions;
</script>

Examples of use:

1. Declaring an input set in the input description section

   comprehensions('[x | x<- [1..100], x*2 >= 12, x<100, x*2<160]');

   will output => [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

2. Using the generated function to modifiy an input array

   let factory = comprehensions('[x | x<- xs, x*2 >= 12, x<100, x*2<160]');
   factory([1,2,3,4,5,6,7,8,9,10]);

   will output => [6, 7, 8, 9, 10]

Quick description of the input spec

The input spec (in short the string passed to the comprehensions function) is composed by three main parts: output function, input set, filter functions.

Taking this spec as example: [x3 | x<- [1..10], x/2>=2, x5<160] we have that:

1. Each specification has to be enclosed in square brackets
2. The portion before the pipe -x*3- is the output function indeed the operation here described will be applied at each value of the array
3. The portion after the pipe and before the first comma -x<- [1..10]- is the input set, here we have some accepted forms:
   1. x<-[first..last] for example x<-[1..10] represent an array composed by the first 10 int [1,2,3,4,5,6,7,8,9,10]
   2. x<-[first,second..last] for example x<-[1,3..10] represent an array where each outut value is evaluated considering the step offset between the first tho values [1,3,5,7,9]
   3. x<-xs considering any kind of array (when this form is used the comprehensionsfunction will be return a factory function especting an input array to which apply the tranformation according to the input spec).
4. The portion after the first array separated by commas -x/2>=2, x*5<16- represents the filter functions

So, if we call the comprehensions function passing the spec example as input we will receive as output [12, 15, 18, 21, 24, 27, 30].

Development

Fetch the dependencies by

npm install

then

Building

npm build

Running test

npm test

License

This project is licensed under the terms of MIT License. See the LICENSE file for more info.