Yes, it is possible to write a terminal emulator with a graphical user interface (GUI) using U++.

Here is a simple example of a terminal emulator with a GUI written in U++ using the Ctrl module:

#include <CtrlLib/CtrlLib.h>

using namespace Upp;

struct TerminalEmulator : public TopWindow {
	// This function is called to process input from the user
	void ProcessInput(const String& input)
	{
		// Process the input and output the result to the console
		console << input << "\n";
	}

	// This function is called to display the prompt and read input from the user
	void ReadLine()
	{
		console << "> ";
	}

	// This function is called when the user presses the Enter key
	void ConsoleKey(dword key, int count)
	{
		if (key == K_ENTER) {
			// Read the input from the console
			String input = console.Get();

			// Process the input
			ProcessInput(input);

			// Clear the console and display the prompt
			console.Clear();
			ReadLine();
		}
	}

	// This function is called when the window is closed
	void ConsoleClose()
	{
		Break();
	}

	// GUI elements
	RichTextView console;

	TerminalEmulator()
	{
		// Set up the console
		console.SetFont(Courier(12));
		console.WhenKey = THISBACK(ConsoleKey);
		console.WhenClose = THISBACK(ConsoleClose);
		Add(console.SizePos());

		// Display the welcome message
		console << "Welcome to the terminal emulator!\n";
		ReadLine();
	}
};

GUI_APP_MAIN
{
	TerminalEmulator().Run();
}

This terminal emulator will display a prompt and a text box where the user can enter input. When the user presses the Enter key, the input will be processed and the result will be displayed in the text box. The program will continue running until the user closes the window.

To compile this program, you will need to have the U++ framework installed on your system. You can then use the upp command-line tool to build the program. For example:

upp terminal_emulator.cpp

This will create an executable file called terminal_emulator that you can run from the terminal.

I hope this helps! Let me know if you have any questions.