simple-patterns's Introduction

Simple Patterns

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The common quote about regular expressions is:

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.

Regular expressions are extremely useful, but they are hard to maintain.

Simple Patterns provides a jQuery-like interface to generating regular expressions.

Examples

To match a username, instead of

let r = /^[a-z0-9_-]{3,16}$/

You can write (and read):

import R$ from 'simple-patterns';
let r = R$.atStart().count(3).to(16).of.charInSet('a-z0-9_-').atEnd();

Instead of this monster IP regex:

let r = /^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$/

You can maintain this:

let r = R$.atStart().count(3).of.group(
   R$.oneOf(
     R$.charInSet('0-9'),
     R$.charInSet('1-9').charInSet('0-9'),
     R$.chr('1').count(2).of.charInSet('0-9'),
     R$.chr('2').charInSet('0-4').charInSet('0-9'),
     R$.text('25').charInSet('0-5'),
   ).then.chr('.')
 ).then.oneOf(
   R$.charInSet('0-9'),
   R$.charInSet('1-9').charInSet('0-9'),
   R$.chr('1').count(2).of.charInSet('0-9'),
   R$.chr('2').charInSet('0-4').charInSet('0-9'),
   R$.text('25').charInSet('0-5'),
).atEnd();

Composable regexes

Since SimplePattern objects are immutable, you can use variables to compose regexes in language that fits your problem space:

For example, rather than match an IP as above, you could define 2 variables to help you:

let octet$ = R$.oneOf(
    R$.charInSet('0-9'),
    R$.charInSet('1-9').charInSet('0-9'),
    R$.chr('1').count(2).of.charInSet('0-9'),
    R$.chr('2').charInSet('0-4').charInSet('0-9'),
    R$.text('25').charInSet('0-5'),
  );

let dot$ = R$.chr('.');

let ip$ = R$.atStart().join(octet$, dot$, octet$, dot$, octet$, dot$, $octet).atEnd();

Now you an use ip$ to match an IP address!