Initial draft of stack-based machine for JS.

The idea I have is that I'll translate/compile JavaScript
into a rudimentary Forth like language.  This sketch forms
the basis for that language's engine.

js4g/StackMachine.h

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+static_assert( __cplusplus >= 2023'02 );
+
+#pragma once
+
+#include <Dillo/Dillo.h>
+
+#include <iostream>
+
+#include <map>
+#include <vector>
+#include <string>
+#include <deque>
+
+namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
+{
+	inline namespace exports
+	{
+		class StackMachine;
+	}
+
+	/*!
+	 * Machine state for JS4G (Java Script Forth Grinder, AKA: JavaScriptForge JS4G).
+	 *
+	 * This class represents the state of a JavaScript execution, post translation to
+	 * the forth grinder format.
+	 */
+	class exports::StackMachine
+	{
+		private:
+			// The main runtime stack of the forth engine.
+			// It grows on the "back".
+			// A `std::deque` is used instead of `std::vector`, because
+			// it helps cut down on large allocations, by subdividing things.
+			std::deque< std::string > stack;
+
+			// TODO: Should these tokens be binary?
+			// Upside: compressed.
+			// Downside: more memory management in the machine end?
+			std::deque< std::string > tokens;
+
+			using Integer= std::int64_t;
+			using Float= long double;
+
+
+			std::map< std::string, std::string > words;
+
+			// Which side of the current conditional to take.
+			enum ConditionalState { If, Else };
+			std::vector< ConditionalState > conditionals;
+
+			ConditionalState currentState;
+
+			void runWord( std::string_view word );
+
+			std::string pop();
+			const std::string &peek();
+
+			void push( std::string s );
+
+			template< typename T >
+			T pop();
+
+			template< typename T >
+			void push( const T &t );
+
+			std::ostream &output;
+
+		public:
+			StackMachine( std::ostream &output= std::cout );
+
+			void
+			loadProgram( std::deque< std::string > tokens )
+			{
+				this->tokens= std::move( tokens );
+			}
+
+			void run();
+	};
+}
+
+namespace Dillo::Hydrogen::JavaScriptForge::inline exports::inline StackMachine_m
+{
+	using namespace detail::StackMachine_m::exports;
+}