From 88e8cab7f91924a217c09b52ddd92935a1f9f186 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Thu, 1 Sep 2016 16:34:44 -0700
Subject: [PATCH] Remove all mention of the ERROR rule type

---
 README.md                     | 12 +++---------
 doc/grammar-schema.json       | 15 ---------------
 src/compiler/parse_grammar.cc | 11 -----------
 3 files changed, 3 insertions(+), 35 deletions(-)

diff --git a/README.md b/README.md
index 6bd5c3f7..d4f4b9b8 100644
--- a/README.md
+++ b/README.md
@@ -74,14 +74,7 @@ int main() {
               "type": "SEQ",
               "members": [
                 {"type": "STRING", "value": "("},
-
-                // Error recovery is controlled by wrapping rule subtrees
-                // in an 'ERROR' rule.
-                {
-                  "type": "ERROR",
-                  "content": {"type": "SYMBOL", "name": "expression"}
-                },
-
+                {"type": "SYMBOL", "name": "expression"},
                 {"type": "STRING", "value": ")"}
               ]
             }
@@ -225,6 +218,7 @@ clang \
 ### References
 
 - [Context Aware Scanning for Parsing Extensible Languages](http://www.umsec.umn.edu/publications/Context-Aware-Scanning-Parsing-Extensible)
-- [LR(1) Parser Generation System](http://arxiv.org/pdf/1010.1234.pdf)  (Error recovery scheme)
 - [Efficient and Flexible Incremental Parsing](http://harmonia.cs.berkeley.edu/papers/twagner-parsing.ps.gz)
 - [Incremental Analysis of Real Programming Languages](http://harmonia.cs.berkeley.edu/papers/twagner-glr.pdf)
+- [Error Detection and Recovery in LR Parsers](http://what-when-how.com/compiler-writing/bottom-up-parsing-compiler-writing-part-13)
+- [Error Recovery for LR Parsers](http://www.dtic.mil/dtic/tr/fulltext/u2/a043470.pdf)
diff --git a/doc/grammar-schema.json b/doc/grammar-schema.json
index 9fc50189..5f43b279 100644
--- a/doc/grammar-schema.json
+++ b/doc/grammar-schema.json
@@ -170,20 +170,6 @@
       "required": ["type", "content"]
     },
 
-    "error-rule": {
-      "type": "object",
-      "properties": {
-        "type": {
-          "type": "string",
-          "pattern": "^ERROR$"
-        },
-        "content": {
-          "$ref": "#/definitions/rule"
-        }
-      },
-      "required": ["type", "content"]
-    },
-
     "prec-rule": {
       "type": "object",
       "properties": {
@@ -246,7 +232,6 @@
         { "$ref": "#/definitions/repeat1-rule" },
         { "$ref": "#/definitions/repeat-rule" },
         { "$ref": "#/definitions/token-rule" },
-        { "$ref": "#/definitions/error-rule" },
         { "$ref": "#/definitions/prec-rule" },
         { "$ref": "#/definitions/prec-left-rule" },
         { "$ref": "#/definitions/prec-right-rule" }
diff --git a/src/compiler/parse_grammar.cc b/src/compiler/parse_grammar.cc
index 5c1c3200..185d919b 100644
--- a/src/compiler/parse_grammar.cc
+++ b/src/compiler/parse_grammar.cc
@@ -86,17 +86,6 @@ ParseRuleResult parse_rule(json_value *rule_json) {
     return { seq(members), "" };
   }
 
-  if (type == "ERROR") {
-    json_value content_json = rule_json->operator[]("content");
-    ParseRuleResult content = parse_rule(&content_json);
-    if (content.rule.get()) {
-      return { content.rule, "" };
-    } else {
-      error_message = "Invalid error content: " + content.error_message;
-      goto error;
-    }
-  }
-
   if (type == "REPEAT") {
     json_value content_json = rule_json->operator[]("content");
     ParseRuleResult content = parse_rule(&content_json);