From e4597ae8f7f33427e715d7d9a393aced5b989734 Mon Sep 17 00:00:00 2001
From: Alec Thomas <alec@swapoff.org>
Date: Sat, 16 May 2020 16:04:08 +1000
Subject: [PATCH] Add a Rules.Merge() helper function.

Might be useful for #363.
---
 regexp.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/regexp.go b/regexp.go
index d13d58d69..96bcce618 100644
--- a/regexp.go
+++ b/regexp.go
@@ -170,6 +170,15 @@ func (r Rules) Clone() Rules {
 	return out
 }
 
+// Merge creates a clone of "r" then merges "rules" into the clone.
+func (r Rules) Merge(rules Rules) Rules {
+	out := r.Clone()
+	for k, v := range rules.Clone() {
+		out[k] = v
+	}
+	return out
+}
+
 // MustNewLexer creates a new Lexer or panics.
 func MustNewLexer(config *Config, rules Rules) *RegexLexer {
 	lexer, err := NewLexer(config, rules)