New, more flexible, parser context datatype that includes and extends

the previous flags allowForest and allowVarRef.
Added binary operator (work in progress).
Better implementation of +=,-=,*=, and /= (new) operators.

token.go

@@ -93,6 +93,15 @@ func (tk *Token) Error() (err error) {
 	return
 }
 
+func (tk *Token) ErrorText() (err string) {
+	if tk.Sym == SymError {
+		if msg, ok := tk.Value.(error); ok {
+			err = msg.Error()
+		}
+	}
+	return
+}
+
 func (tk *Token) Errors(msg string) (err error) {
 	err = fmt.Errorf("[%d:%d] %v", tk.row, tk.col, msg)
 	return
@@ -108,6 +117,6 @@ func (tk *Token) ErrorExpectedGotString(symbol, got string) (err error) {
 }
 
 func (tk *Token) ErrorExpectedGotStringWithPrefix(prefix, symbol, got string) (err error) {
-	err = fmt.Errorf("[%d:%d] %s `%s`, got `%s`", tk.row, tk.col, prefix, symbol, got)
+	err = fmt.Errorf("[%d:%d] %s %s, got `%s`", tk.row, tk.col, prefix, symbol, got)
 	return
 }