Partially working with nested conditionals.

Some of the conditional-skip code is a bit wrong...

js4g/StackMachine.cc

@@ -7,6 +7,11 @@ static_assert( __cplusplus >= 2023'02 );
 namespace
 {
 	using namespace std::literals::string_literals;
+
+	namespace C
+	{
+		constexpr bool debug= false or true;
+	}
 }
 
 namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
@@ -21,22 +26,53 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 	{
 		while( not tokens.empty() )
 		{
-			const auto token= tokens.front();
+			runWord( next() );
-			tokens.pop_front();
 
-			runWord( token );
+			if( C::debug ) std::cerr << "After processing stack is now: " << std::endl;
+			if( C::debug ) std::copy( rbegin( stack ), rend( stack ), std::ostream_iterator< std::string >{ std::cerr, "\n" } );
 		}
 
-		std::cerr << "Run done with stack at size: " << stack.size() << std::endl;
+		if( C::debug ) std::cerr << "Run done with stack at size: " << stack.size() << std::endl;
+	}
+
+	std::string
+	StackMachine::next()
+	{
+		if( tokens.empty() )
+		{
+			throw std::runtime_error{ "FATAL: Token required, no more tokens left." };
+		}
+
+		const auto rv= tokens.front();
+		tokens.pop_front();
+		return rv;
 	}
 
 	void
 	StackMachine::runWord( const std::string_view word )
 	{
+		if( C::debug ) std::cerr << "Processing token: " << word << std::endl;
 		const bool inConditional= not conditionals.empty();
 
 		if( false );
 		else if( word.empty() );
+		else if( word == "@enddef" )
+		{
+			if( not definition.has_value() )
+			{
+				throw std::runtime_error{ "Stray end of function definition" };
+			}
+
+			if( C::debug ) std::cerr << "Definition of " << definition.value() << " is done.  It is: " << std::endl;
+			if( C::debug ) std::copy( begin( words.at( definition.value() ) ), end( words.at( definition.value() ) ),
+					std::ostream_iterator< std::string >{ std::cout, "\n" } );
+			definition= std::nullopt;
+		}
+		else if( definition.has_value() )
+		{
+			if( C::debug ) std::cerr << "Adding word: " << word << " to function definition: " << definition.value() << std::endl;
+			words[ definition.value() ].emplace_back( word );
+		}
 		else if( inConditional and word == "@else" and currentState != Else )
 		{
 			currentState= Else;
@@ -44,11 +80,18 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 		else if( inConditional and word == "@endif" )
 		{
 			conditionals.pop_back();
+			currentState= resumeConditionals.back();
+			resumeConditionals.pop_back();
 		}
 		else if( inConditional and currentState != conditionals.back() )
 		{
-			// Pass (We skip things inside the wrong side)
+			if( word != "@if" )
-			// TODO: Nested if's won't work, here...
+			{
+				conditionals.push_back( Skipped );
+				resumeConditionals.push_back( currentState );
+				currentState= If;
+			}
+			else ; // We skip the statement.
 		}
 		else if( word == "@else" )
 		{
@@ -63,6 +106,13 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 			auto val= peek();
 			push( std::move( val ) );
 		}
+		else if( word == "@swap" )
+		{
+			auto a= pop();
+			auto b= pop();
+			push( std::move( a ) );
+			push( std::move( b ) );
+		}
 		else if( word == "@drop" )
 		{
 			std::ignore= pop();
@@ -72,6 +122,14 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 			auto val= pop< Integer >();
 			push( val == 0 ? 1 : 0 );
 		}
+		else if( word == "@i_inc" )
+		{
+			push( pop< Integer >() + 1 );
+		}
+		else if( word == "@i_dec" )
+		{
+			push( pop< Integer >() - 1 );
+		}
 		else if( word == "@i_add" )
 		{
 			const auto lhs= pop< Integer >();
@@ -108,12 +166,31 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 		{
 			const auto val= pop< Integer >();
 			conditionals.push_back( val ? If : Else );
+			resumeConditionals.push_back( currentState );
 			currentState= If;
 		}
+		else if( word == "@define" )
+		{
+			if( definition.has_value() ) throw std::runtime_error{ "Nested definitions not supported." };
+
+			definition= next();
+
+			if( C::debug ) std::cerr << "Starting function definition for " << definition.value() << std::endl;
+		}
 		else if( word.at( 0 ) == '@' )
 		{
-			throw std::runtime_error{ "Unknown keyword: `"s + std::string{ word }
+			const std::string invoke{ word.substr( 1 ) };
-					+ "`" };
+			if( not words.contains( invoke ) )
+			{
+				throw std::runtime_error{ "Unknown keyword: `"s + std::string{ word }
+						+ "`" };
+			}
+
+			const auto &def= words.at( invoke );
+
+			std::copy( rbegin( def ), rend( def ), front_inserter( tokens ) );
+
+			if( tokens.size() >= 1000 ) abort();
 		}
 		else
 		{

js4g/StackMachine.h

@@ -42,14 +42,20 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 			using Float= long double;
 
 
-			std::map< std::string, std::string > words;
+			std::map< std::string, std::vector< std::string > > words;
 
 			// Which side of the current conditional to take.
-			enum ConditionalState { If, Else };
+			enum ConditionalState { If, Else, Skipped };
 			std::vector< ConditionalState > conditionals;
+			std::vector< ConditionalState > resumeConditionals;
 
 			ConditionalState currentState;
 
+			std::optional< std::string > definition;
+
+			std::ostream &output;
+
+
 			void runWord( std::string_view word );
 
 			std::string pop();
@@ -63,7 +69,7 @@ namespace Dillo::Hydrogen::JavaScriptForge	::detail::  StackMachine_m
 			template< typename T >
 			void push( const T &t );
 
-			std::ostream &output;
+			std::string next();
 
 		public:
 			StackMachine( std::ostream &output= std::cout );

js4g/factorial.js4

@@ -0,0 +1,43 @@
+@define factorial
+	@dup
+	@if
+		@dup @i_dec
+		@factorial
+		@i_mul
+	@else
+		@i_inc
+	@endif
+@enddef
+
+6 @factorial
+@print
+
+
+@define fib
+	@dup
+	@not
+	@if
+		@drop 1
+	@else
+		@dup
+		@i_dec
+		@not
+		@if
+			@drop 1
+		@else
+			@i_dec
+			@dup
+			@i_dec
+			@fib
+			@swap
+			@fib
+			@i_add
+		@endif
+	@endif
+@enddef
+
+
+8 @fib @print
+
+10 @factorial
+@print

js4g/fib.js4

@@ -0,0 +1,26 @@
+@define fib
+	@dup
+	@not
+	@if
+		@drop 1
+	@else
+		@dup
+		@i_dec
+		@not
+		@if
+			@drop 1
+		@else
+			@i_dec
+			@dup
+			@i_dec
+			@fib
+			@swap
+			@fib
+			@i_add
+		@endif
+	@endif
+@enddef
+
+
+9 @dup @print @fib @print
+