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.

symbol-map.go

@@ -91,6 +91,7 @@ func init() {
 		SymDoubleDot:       {"..", symClassOperator},     //  58: '..'
 		SymTripleDot:       {"...", symClassOperator},    //  59: '...'
 		SymStarEqual:       {"*=", symClassOperator},     //  60: '*='
+		SymSlashEqual:      {"/=", symClassOperator},     //  61: '/='
 		// SymChangeSign
 		// SymUnchangeSign
 		// SymIdentifier
@@ -140,16 +141,21 @@ func SymToString(sym Symbol) string {
 
 func SymListToString(symList []Symbol, quote bool) string {
 	var sb strings.Builder
-	for _, sym := range symList {
-		if sb.Len() > 0 {
-			sb.WriteByte(',')
-		}
-		if quote {
-			sb.WriteByte('\'')
-		}
-		sb.WriteString(SymToString(sym))
-		if quote {
-			sb.WriteByte('\'')
+	if len(symList) == 0 {
+		sb.WriteString("<nothing>")
+	} else {
+		for _, sym := range symList {
+			if sb.Len() > 0 {
+				sb.WriteByte(',')
+				sb.WriteByte(' ')
+			}
+			if quote {
+				sb.WriteByte('`')
+			}
+			sb.WriteString(SymToString(sym))
+			if quote {
+				sb.WriteByte('`')
+			}
 		}
 	}
 	return sb.String()