Add BISON-style location tracking.

Author: danswartzendruber

cmd/goyacc/yacc.go

@@ -258,6 +258,8 @@ var nerrors = 0                   // number of errors
 // assigned token type values
 
 var extval = 0
+var firsttok = 0
+var lasttok = 0
 
 // grammar rule information
 
@@ -698,6 +700,12 @@ outer:
 		// non-literals
 		if !tokset[i].noconst {
 			fmt.Fprintf(ftable, "const %v = %v\n", tokset[i].name, tokset[i].value)
+			if firsttok == 0 {
+				firsttok = tokset[i].value
+			}
+			if lasttok == 0 && i == ntokens {
+				lasttok = tokset[i].value
+			}
 		}
 	}
 
@@ -709,6 +717,11 @@ outer:
 	}
 	fmt.Fprintf(ftable, "}\n")
 
+	fmt.Fprintf(ftable, "\n")
+	fmt.Fprintf(ftable, "var %sFirsttok = %d\n", prefix, firsttok)
+	fmt.Fprintf(ftable, "var %sLasttok = %d\n", prefix, lasttok)
+	fmt.Fprintf(ftable, "\n")
+
 	// put out names of states.
 	// commented out to avoid a huge table just for debugging.
 	// re-enable to have the names in the binary.
@@ -3296,9 +3309,14 @@ func $$NewParser() $$Parser {
 const $$Flag = -1000
 
 func $$Tokname(c int) string {
-	if c >= 1 && c-1 < len($$Toknames) {
-		if $$Toknames[c-1] != "" {
-			return $$Toknames[c-1]
+     offset := 1
+     if c >= $$Private {
+          offset = $$Private-1
+     }
+
+	if c >= offset && c-offset < len($$Toknames) {
+		if $$Toknames[c-offset] != "" {
+			return $$Toknames[c-offset]
 		}
 	}
 	return __yyfmt__.Sprintf("tok-%v", c)