From 5656d9d42f76202a534ad640d3a4e287e0e40418 Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@gmail.com>
Date: Fri, 31 May 2024 10:00:09 +0100
Subject: [PATCH] feat(parsely): Add a fail() parser

I've found this useful for stubbing out parts of a grammar during
development.
---
 packages/phoenix/packages/parsely/exports.js          |  3 ++-
 .../phoenix/packages/parsely/parsers/terminals.js     | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/packages/phoenix/packages/parsely/exports.js b/packages/phoenix/packages/parsely/exports.js
index b729a589..29f956b9 100644
--- a/packages/phoenix/packages/parsely/exports.js
+++ b/packages/phoenix/packages/parsely/exports.js
@@ -1,6 +1,6 @@
 import { adapt_parser, VALUE } from './parser.js';
 import { Discard, FirstMatch, Optional, Repeat, Sequence } from './parsers/combinators.js';
-import { Literal, None, StringOf, Symbol } from './parsers/terminals.js';
+import { Fail, Literal, None, StringOf, Symbol } from './parsers/terminals.js';
 
 class ParserWithAction {
     #parser;
@@ -81,6 +81,7 @@ export class GrammarContext {
 export const standard_parsers = () => {
     return {
         discard: Discard,
+        fail: Fail,
         firstMatch: FirstMatch,
         literal: Literal,
         none: None,
diff --git a/packages/phoenix/packages/parsely/parsers/terminals.js b/packages/phoenix/packages/parsely/parsers/terminals.js
index 10936540..62c19df6 100644
--- a/packages/phoenix/packages/parsely/parsers/terminals.js
+++ b/packages/phoenix/packages/parsely/parsers/terminals.js
@@ -91,3 +91,14 @@ export class None extends Parser {
         return { status: VALUE, $: 'none', $discard: true };
     }
 }
+
+/**
+ * Always fails parsing.
+ */
+export class Fail extends Parser {
+    _create () {}
+
+    _parse (stream) {
+        return UNRECOGNIZED;
+    }
+}