examples: don't demonstrate multistart, which is not part of 3.8

Besides, for mysterious reasons, this fails on some environment.
Reported by Dagobert Michelsen.
<https://lists.gnu.org/archive/html/bug-bison/2021-08/msg00008.html>

* examples/c/lexcalc/lexcalc.test, examples/c/lexcalc/parse.y,
* examples/c/lexcalc/scan.l: Revert to a single-start example.

examples/c/lexcalc/lexcalc.test

@@ -38,26 +38,9 @@ run -noerr 0 9 -p
 cat >input <<EOF
 (1+2) *
 EOF
-run 1 'err: 1.8-2.0: syntax error, unexpected end of line, expecting ( or number
-err: errors: 1'
+run 1 'err: 1.8-2.0: syntax error, unexpected end of line, expecting ( or number'
 
 cat >input <<EOF
 1 / (2 - 2)
 EOF
-run 1 'err: 1.1-11: error: division by zero
-err: errors: 1'
-
-
-# Multistart: parse "expression" instead of "input".
-cat >input <<EOF
-1+2*3
-EOF
-run 0 'expression: 7' -e
-
-cat >input <<EOF
-1
-2
-EOF
-run 1 'expression: failure
-err: 2.1: syntax error, unexpected number, expecting end of file
-err: errors: 1' -e
+run 1 'err: 1.1-11: error: division by zero'

examples/c/lexcalc/parse.y

@@ -25,10 +25,10 @@
 {
   // Tell Flex the expected prototype of yylex.
 #define YY_DECL                                 \
-  yytoken_kind_t yylex (YYSTYPE* yylval, YYLTYPE *yylloc)
+  yytoken_kind_t yylex (YYSTYPE* yylval, YYLTYPE *yylloc, int *nerrs)
   YY_DECL;
 
-  void yyerror (const YYLTYPE *loc, const char *msg);
+  void yyerror (const YYLTYPE *loc, int *nerrs, const char *msg);
 }
 
 // Emitted on top of the implementation file.
@@ -62,6 +62,9 @@
 // Enable debug traces (see yydebug in main).
 %define parse.trace
 
+// Error count, exchanged between main, yyparse and yylex.
+%param {int *nerrs}
+
 %token
   PLUS   "+"
   MINUS  "-"
@@ -73,11 +76,9 @@
 ;
 
 %token <int> NUM "number"
-%type <int> exp expression line
+%type <int> exp
 %printer { fprintf (yyo, "%d", $$); } <int>
 
-%start input expression NUM
-
 // Precedence (from lowest to highest) and associativity.
 %left "+" "-"
 %left "*" "/"
@@ -90,12 +91,8 @@ input:
 ;
 
 line:
-  exp EOL   { $$ = $exp; printf ("%d\n", $$); }
-| error EOL { $$ = 0; yyerrok; }
-;
-
-expression:
-  exp EOL  { $$ = $exp; }
+  exp EOL   { printf ("%d\n", $exp); }
+| error EOL { yyerrok; }
 ;
 
 exp:
@@ -106,7 +103,7 @@ exp:
   {
     if ($3 == 0)
       {
-        yyerror (&@$, "error: division by zero");
+        yyerror (&@$, nerrs, "error: division by zero");
         YYERROR;
       }
     else
@@ -118,41 +115,24 @@ exp:
 %%
 // Epilogue (C code).
 
-void yyerror (const YYLTYPE *loc, const char *msg)
+void yyerror (const YYLTYPE *loc, int *nerrs, const char *msg)
 {
   YYLOCATION_PRINT (stderr, loc);
   fprintf (stderr, ": %s\n", msg);
+  ++*nerrs;
 }
 
 int main (int argc, const char *argv[])
 {
   // Possibly enable parser runtime debugging.
   yydebug = !!getenv ("YYDEBUG");
-  int parse_expression_p = 0;
-  int nerrs = 0;
-
   // Enable parse traces on option -p.
   for (int i = 1; i < argc; ++i)
-    if (strcmp (argv[i], "-e") == 0)
-      parse_expression_p = 1;
-    else if (strcmp (argv[i], "-p") == 0)
+    if (strcmp (argv[i], "-p") == 0)
       yydebug = 1;
 
-  if (parse_expression_p)
-    {
-      yyparse_expression_t res = yyparse_expression ();
-      nerrs = res.yynerrs;
-      if (res.yystatus == 0)
-        printf ("expression: %d\n", res.yyvalue);
-      else
-        printf ("expression: failure\n");
-    }
-  else
-    nerrs = yyparse_input ().yynerrs;
-
-  if (nerrs)
-    fprintf (stderr, "errors: %d\n", nerrs);
-
+  int nerrs = 0;
+  yyparse (&nerrs);
   // Exit on failure if there were errors.
   return !!nerrs;
 }

examples/c/lexcalc/scan.l

@@ -61,7 +61,7 @@
   errno = 0;
   long n = strtol (yytext, NULL, 10);
   if (! (INT_MIN <= n && n <= INT_MAX && errno != ERANGE))
-    yyerror (yylloc, "integer is out of range");
+    yyerror (yylloc, nerrs, "integer is out of range");
   yylval->TOK_NUM = (int) n;
   return TOK_NUM;
 }
@@ -71,7 +71,7 @@
  /* Ignore white spaces. */
 [ \t]+   LOCATION_STEP (); continue;
 
-.        yyerror (yylloc, "syntax error, invalid character"); continue;
+.        yyerror (yylloc, nerrs, "syntax error, invalid character"); continue;
 
 <<EOF>>  return TOK_YYEOF;
 %%