From 60366b152be3f46abdf1756b712205a4bc2fc7d4 Mon Sep 17 00:00:00 2001
From: Akim Demaille <akim.demaille@gmail.com>
Date: Sat, 25 Apr 2020 15:03:01 +0200
Subject: [PATCH] examples: bistromathic: demonstrate error recovery

* examples/c/bistromathic/parse.y: here.
* examples/c/bistromathic/bistromathic.test: Check it.
Included a stupid case where the error is actually ignored.
---
 examples/c/README.md                      |  1 +
 examples/c/bistromathic/README.md         |  1 +
 examples/c/bistromathic/bistromathic.test | 21 ++++++++++++++++++---
 examples/c/bistromathic/parse.y           |  1 +
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/examples/c/README.md b/examples/c/README.md
index 47963f13..0d8031c3 100644
--- a/examples/c/README.md
+++ b/examples/c/README.md
@@ -53,6 +53,7 @@ push-parser model.
 This example demonstrates best practices when using Bison.
 - Its hand-written scanner tracks locations.
 - Its interface is pure.
+- It uses the `error` token to get error recovery.
 - Its interface is "incremental", well suited for interaction: it uses the
   push-parser API to feed the parser with the incoming tokens.
 - It features an interactive command line with completion based on the
diff --git a/examples/c/bistromathic/README.md b/examples/c/bistromathic/README.md
index 6b6521de..05f1b7ed 100644
--- a/examples/c/bistromathic/README.md
+++ b/examples/c/bistromathic/README.md
@@ -2,6 +2,7 @@
 This example demonstrates best practices when using Bison.
 - Its hand-written scanner tracks locations.
 - Its interface is pure.
+- It uses the `error` token to get error recovery.
 - Its interface is "incremental", well suited for interaction: it uses the
   push-parser API to feed the parser with the incoming tokens.
 - It features an interactive command line with completion based on the
diff --git a/examples/c/bistromathic/bistromathic.test b/examples/c/bistromathic/bistromathic.test
index c32c1f45..629c32c5 100755
--- a/examples/c/bistromathic/bistromathic.test
+++ b/examples/c/bistromathic/bistromathic.test
@@ -82,11 +82,26 @@ run 0 '> 1 / 0
 > ''
 err: 1.1-5: error: division by zero'
 
+# Error recovery.
 cat >input <<EOF
-100%
+((1 ++ 2) ** 3)
+(1 ++ 2) + (3 ** 4)
 EOF
-run 0 '> 100%
-100
+run 0 '> ((1 ++ 2) ** 3)
+666
+> (1 ++ 2) + (3 ** 4)
+1332
+> ''
+err: 1.6: syntax error: expected - or ( or number or function or variable before +
+err: 2.5: syntax error: expected - or ( or number or function or variable before +
+err: 2.16: syntax error: expected - or ( or number or function or variable before *'
+
+# This is really stupid: we just discarded % and did not enter error recovery.
+cat >input <<EOF
+100% + 10
+EOF
+run 0 '> 100% + 10
+110
 > ''
 err: 1.4: error: invalid character'
 
diff --git a/examples/c/bistromathic/parse.y b/examples/c/bistromathic/parse.y
index 607a6ef4..5d422651 100644
--- a/examples/c/bistromathic/parse.y
+++ b/examples/c/bistromathic/parse.y
@@ -146,6 +146,7 @@ exp:
 | "-" exp  %prec NEG { $$ = -$2; }
 | exp[l] "^" exp[r]  { $$ = pow ($l, $r); }
 | "(" exp ")"        { $$ = $2; }
+| "(" error ")"      { $$ = 666; }
 ;
 
 // End of grammar.