examples: d: fix the handling of unary +

It was interpreting "+exp" as "-exp".

* examples/d/calc.y: Fix.
* examples/d/calc.test: Check it.

examples/d/calc.test

@@ -20,6 +20,16 @@ cat >input <<EOF
 EOF
 run 0 7
 
+cat >input <<EOF
++1 + +2 * +3
+EOF
+run 0 7
+
+cat >input <<EOF
+-1 + -2 * -3
+EOF
+run 0 5
+
 cat >input <<EOF
 1 + 2 * * 3
 EOF

examples/d/calc.y

@@ -61,7 +61,7 @@ exp:
 | exp "-" exp          { $$ = $1 - $3; }
 | exp "*" exp          { $$ = $1 * $3; }
 | exp "/" exp          { $$ = $1 / $3; }
-| "+" exp  %prec UNARY { $$ = -$2; }
+| "+" exp  %prec UNARY { $$ = $2; }
 | "-" exp  %prec UNARY { $$ = -$2; }
 | "(" exp ")"          { $$ = $2; }
 ;