op.cs

Expression expr = YacqServices.Parse("Int32.(Parse '123').(ToString 'x2')");
SerializedExpression serializedExpr = YacqExpression.Serialize(expr);
var dumpedString = serializedExpr.SaveText();
SerializedExpression deserializedExpr = YacqExpression.LoadText(dumpedString);
expr = deserializedExpr.Reduce();

yacq-serialize.xml

<?xml version="1.0"?>
<!-- Int32.(Parse '123').(ToString 'x2')
  => Int32.Parse("123").ToString("x2")
-->
<expression z:Id="i1" i:type="Call" xmlns="http://yacq.net/schema" xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns:z="http://schemas.microsoft.com/2003/10/Serialization/">
  <Arguments>
    <Node z:Id="i2" i:type="Constant">
      <Type>
        <Token>33554508</Token>
      </Type>
      <Value i:type="a:string" xmlns:a="http://www.w3.org/2001/XMLSchema">x2</Value>
    </Node>
  </Arguments>
  <Method>
    <Token>100666711</Token>
  </Method>
  <Object z:Id="i3" i:type="Call">
    <Arguments>
      <Node z:Id="i4" i:type="Constant">
        <Type>
          <Token>33554508</Token>
        </Type>
        <Value i:type="a:string" xmlns:a="http://www.w3.org/2001/XMLSchema">123</Value>
      </Node>
    </Arguments>
    <Method>
      <Token>100666714</Token>
    </Method>
  </Object>
</expression>