Generates regular expressions that match a set of strings.
The simplest use is to simply pass an array of strings to regexgen
:
const regexgen = require('regexgen');
regexgen(['foobar', 'foobaz', 'foozap', 'fooza']); // => /foo(?:zap?|ba[rz])/
You can also use the Trie
class directly:
const {Trie} = require('regexgen');
let t = new Trie;
t.add('foobar');
t.add('foobaz');
t.toRegExp(); // => /fooba[rz]/
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Generate a Trie containing all of the input strings. This is a tree structure where each edge represents a single character. This removes redundancies at the start of the strings, but common branches further down are not merged.
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A trie can be seen as a tree-shaped deterministic finite automaton (DFA), so DFA algorithms can be applied. In this case, we apply Hopcroft's DFA minimization algorithm to merge the nondistinguishable states.
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Convert the resulting minimized DFA to a regular expression. This is done using Brzozowski's algebraic method, which is quite elegant. It expresses the DFA as a system of equations which can be solved for a resulting regex. Along the way, some additional optimizations are made, such as hoisting common substrings out of an alternation, and using character class ranges. This produces an an Abstract Syntax Tree (AST) for the regex, which is then converted to a string and compiled to a JavaScript
RegExp
object.
MIT