d: improve the example

* examples/d/calc.y: Exit with failure on errors.
Remove useless operators (=, !) meant for the test suite.
Add unary + for symmetry.
* examples/d/calc.test: Adjust expectations.

examples/d/calc.test

@@ -23,4 +23,4 @@ run 0 7
 cat >input <<EOF
 1 + 2 * * 3
 EOF
-run 0 "err: syntax error, unexpected *, expecting - or ! or ( or number"
+run 1 "err: syntax error, unexpected *, expecting + or - or ( or number"

examples/d/calc.y

@@ -18,17 +18,15 @@
        MINUS  "-"
        STAR   "*"
        SLASH  "/"
-       BANG   "!"
        LPAR   "("
        RPAR   ")"
        EOL    "end of line"
 %token <ival> NUM "number"
 %type  <ival> exp
 
-%nonassoc "="       /* comparison            */
 %left "-" "+"
 %left "*" "/"
-%precedence NEG     /* negation--unary minus */
+%precedence UNARY   /* unary operators */
 
 /* Grammar follows */
 %%
@@ -45,28 +43,20 @@ line:
 
 exp:
   NUM                  { $$ = $1; }
-| exp "=" exp
-  {
-    if ($1 != $3)
-      yyerror (format ("calc: error: %d != %d", $1, $3));
-  }
 | exp "+" exp          { $$ = $1 + $3; }
 | exp "-" exp          { $$ = $1 - $3; }
 | exp "*" exp          { $$ = $1 * $3; }
 | exp "/" exp          { $$ = $1 / $3; }
-| "-" exp  %prec NEG { $$ = -$2; }
+| "+" exp  %prec UNARY { $$ = -$2; }
+| "-" exp  %prec UNARY { $$ = -$2; }
 | "(" exp ")"          { $$ = $2; }
-| "(" error ")"      { $$ = 1111; }
-| "!"                { $$ = 0; return YYERROR; }
-| "-" error          { $$ = 0; return YYERROR; }
 ;
 
-
 %%
 class CalcLexer : Lexer {
 
-  this ()
-    {}
+  // Should be a local in main, shared with %parse-param.
+  int exit_status = 0;
 
   int
   get_char ()
@@ -84,6 +74,7 @@ class CalcLexer : Lexer {
 
   public void yyerror (string s)
   {
+    exit_status = 1;
     stderr.writeln (s);
   }
 
@@ -141,7 +132,6 @@ class CalcLexer : Lexer {
       case '-': return YYTokenType.MINUS;
       case '*': return YYTokenType.STAR;
       case '/': return YYTokenType.SLASH;
-      case '!': return YYTokenType.BANG;
       case '(': return YYTokenType.LPAR;
       case ')': return YYTokenType.RPAR;
       case '\n': return YYTokenType.EOL;
@@ -150,9 +140,10 @@ class CalcLexer : Lexer {
   }
 }
 
-void main ()
+int main ()
 {
   CalcLexer l = new CalcLexer ();
   Calc p = new Calc (l);
   p.parse ();
+  return l.exit_status;
 }