Uses MtxParseExpr, MtxParseClass; procedure Example(myParser: TMtxExpression); var eCount: Integer; begin // 1. Example myParser.DefineDouble('omega'); myParser.DefineDoubleConstant('hbar'); myParser.AddExpr('hbar*omega'); // 2. Clear everything myParser.ClearAll; // 3. What happened ? eCount := myParser.ExprCount // returns 0 // Also, all defined the variable, constant varying function, operator, // etc.. lists are cleared. end;