Keywords: Xamarin.Forms, Prolog, C#Prolog, CSProlog, PCL Storage, Command Prompt    I didn't update this blog for a while, but I came to want to enjoy Prolog programming and I re-started application development.  First of all, I post an application, Prolog Interpreter, that I almost developed before.  The Prolog Interpreter App has been developed with a Xamarin Library, CSProlog, based on the Command Prompt App  that I posted before.      The source code is here .     Since MainPage.xaml, MainPage.xaml.cs, ComInterpreter.cs, CommandExecute.cs, PCLStorage.cs are the same as the ones in Command Prompt App , I skip their description and introduce Prolog.cs beriefly below.   I developed Prolog.cs with reference to some sample programs.  Obviously, one of the NuGet packages, CSProlog, are added to this project.    Prolog.cs   //using System.Text;   //#define SystemIO  #define PCLStorage   // #define iOS   using System.Collections.Generic;  using System.Linq;   #if SystemIO  ...