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Building a Programming Language: Part II (Adding Conditions, Loop and Blocks to BrainLess)

, 11 Oct 2013 LGPL3
In this article, we will discuss implementing conditional statements, loops and blocks.
/*
Author : Shakti Misra
All are welcome to use these files, distribute, modify and release. But This notice should be included.
This software is given as is, for use and modification.
*/

#include "Interpreter.h"

#define START_RESTORE_PT( a ) const long a( m_lex.setRestorePoint() )
#define END_RESTORE_PT( a ) 

void Interpreter::interpreteScript()//Main routine to start script interpretation. this is semantic analysis or meaning findout method.
{
	m_lex.getNextToken();
	while( eTokenOver != m_lex.getCurrentToken() )
	{
		enmTokens tok = m_lex.getCurrentToken();//shakti del
		Sentence();
		tok = m_lex.getCurrentToken();
	}
}

// #B(<Block-Name>:<Block-Content>) - for defining a block, which translates to as below
// eBlock eLeftParen (eCharVal)+ eColon eRightParen
// #B(<Block-Name>) calls a block which translate into
// eBlock eLeftParen (eCharVal)+ eRightParen 
void Interpreter::Block()
{
	/*
	A block is of the form #B(BlockName)[BlockContent]
	*/
	char szBlockName[BLOCK_NAME_SIZE] = {0};
	static unsigned int functionCount(0);

	if( eLeftParen == m_lex.getNextToken() )//#B already consumed, check if we have a (
	{
		int index = 0;

		//Get the block name and store it
		while( (eCharVal == m_lex.getNextToken()) //Any thing after ( is a block names
			&& (index < BLOCK_NAME_SIZE) 
			)
		{
			szBlockName[index++] = (char)m_lex.getAttribVal(); //extract the name
		}


		if((index > BLOCK_NAME_SIZE) || 
			isBlankOrNull(szBlockName))
		{
			printf("Invalid block name [ %s ].\n", szBlockName);//TODO proper error handling
		}

		/*Now if we find a ":" like #B(<NAME>: we know that a body follows.
		When a body follows, we jbust store the body starting location with the block name
		in a map. So when the block is called as #B(<NAME>) we can execute the code.
		This is done by searching the map for the name, get the index and repositdion the 
		cursor to that position.
		*/
		if(eColon == m_lex.getCurrentToken())
		{
			//Store the name and the index
			pair<symTable::iterator, bool> ret = 
				m_funSymTable.insert( 
				pair<string, ulong>( szBlockName, m_lex.getTokenIndex() ) 
				);
			
			//If false is returned, then the block is already defined.
			//re definition of block not possible.
			if(false == ret.second)
			{
				printf("Function [ %s ] already defined. Do you want to call it?\n", szBlockName);
			}

			unsigned int parenCount(1); //Already we have seen one (

			while( eTokenOver != m_lex.getNextToken())
			{
				if(eLeftParen == m_lex.getCurrentToken())
					++parenCount;
				else if(eRightParen == m_lex.getCurrentToken())
					--parenCount;
				if(0 == parenCount)
					break;
			}
		}//if(eColon == m_lex.getCurrentToken()) end
		else if(eRightParen == m_lex.getCurrentToken())
		{/*
		 if instead of ":" we see a ")" then we know that its a block call. 
		 */
			if( m_funSymTable.empty() )
			{
				printf("No functions defined.\n");
				return;
			}
			
			++functionCount;
			//Search for the block name and find the location
			const symTable::iterator it = m_funSymTable.find( szBlockName );
			if( it == m_funSymTable.end() )
			{
				printf("Function not found.\n");
				return;
			}

			//Before going there, store the return address, so after  block is 
			//executed we can return to this place.
			const ulong returnAddress = m_lex.getTokenIndex();
			m_lex.setTokenIndex( it->second );
			while(eTokenOver != m_lex.getNextToken())
			{
				if(eRightParen == m_lex.getCurrentToken())
				{// When we find ) we know a function body ends, so return
					--functionCount;
					//Set the index before retrning.
					m_lex.setTokenIndex( returnAddress );
					break;
				}
				ExecuteSentence();//If ")" not found block bodt still remaining
			}
			return;
		}//else if(eRightParen == m_lex.getCurrentToken()) end
		else
		{
			printf("Unknown token in Block.\n");
		}
	}
	else
	{
		printf("Not a valid block.\n");
	}
	return;
}

void Interpreter::ExecuteSentence()
{
enmTokens tok = m_lex.getCurrentToken();//shakti del
switch(m_lex.getCurrentToken())
{//Based on the tokens choose the path.
case eRdAndStrVal:
	m_tapeVirtualMachine.getCharAndStore();break;
case eCharVal:break;//TODO
	/*        case eBackSlash:
	compareWithNext();break;
	*/
case eDspCurVal:
	m_tapeVirtualMachine.displayChar();break;
case eIncrContent:
	m_tapeVirtualMachine.incrementContent();break;
case eDecrContent:
	m_tapeVirtualMachine.decrementContent();break;
case eAddWithNext:
	m_tapeVirtualMachine.addWithNext();break;
case eSubNext:
	m_tapeVirtualMachine.substractFromNext();break;
case eStarChar:
	m_tapeVirtualMachine.moveHeadForeward();break;
case eLeftAngleBracket:
	m_tapeVirtualMachine.moveHeadBackward();break;
case eLessThan:// \<
case eGreaterThan:// \>
case eEquality:// \=
	compareWithNextBoolean();break;
case eCompareGeneral://\<>
	compareWithNext();break;
case eExclaimationMark:
	intDisplayContent();
	tok = m_lex.getCurrentToken();
	break;
case eIF://IF(\<)...FI
case eFI://FI dispatch control to IF block code only, it knows how to handle this
	IFBlock();
	tok = m_lex.getCurrentToken();
	break;
case eBlock://#B(BlockName:BlockBody)
	Block();break;
case eDO://DO...DONE
	DOLoop();//No case for "DONE". DONE is consumed in DOLoop function
	break;
default:
	tok = m_lex.getCurrentToken();
	exit(0);
	break;//TODO error handling
}
}

void Interpreter::Sentence()
{
	ExecuteSentence();
	enmTokens tok = m_lex.getCurrentToken();
	tok = m_lex.getNextToken();//Advance the token
}

//This is for the DO...DONE loop
//Till the flag register is 1 it will execute the code inside the DO and DONE block
void Interpreter::DOLoop()
{
	ulong startPoint(m_lex.getTokenIndex());
	ulong endPoint(0);
	while( HEX_1 ^ m_tapeVirtualMachine.getFlagRegister() )
	{
		while( eTokenOver != m_lex.getNextToken() )
		{
			if(eDONE == m_lex.getCurrentToken())
			{
				endPoint = m_lex.getTokenIndex();
				m_lex.setTokenIndex(startPoint);
				break;
			}
			ExecuteSentence();
		}
	}
	if(endPoint > 0)
		m_lex.setTokenIndex(endPoint);
	else//It hasnt gone inside the above loop so we need to consume till the DONE
	{
		unsigned int doCount(1);
		while( eTokenOver != m_lex.getNextToken() )
		{
			if(eDONE == m_lex.getNextToken())
				--doCount;
			else if(eDO == m_lex.getNextToken())
				++doCount;
			if(0 == doCount)
				return;
		}
	}
}

void Interpreter::intDisplayContent()
{   //When we are in this function we know that it was due to ![eExclaimationMark] that this function is called.
	//So check for eLeftSqrParen eIntNumber eRightSqrParen structure.
	switch(m_lex.getNextToken())//The tokens group eExclaimationMark eLeftSqrParen eIntNumber eRightSqrParen is a valid token.
	{
	case eLeftSqrParen:
		int len(0);
		if(eIntNumber == m_lex.getNextToken())
		{
			len = (int)m_lex.getAttribVal();
		}
		if(eRightSqrParen == m_lex.getNextToken())
		{
			m_tapeVirtualMachine.displayMultiChar(len);
		}
	}
}

void Interpreter::compareWithNextBoolean()
{
	compareWithNext();

	const ulong flagVal = m_tapeVirtualMachine.getFlagRegister();
	bool valSet = false;

	switch( m_lex.getCurrentToken() )
	{
	case eLessThan:
		if(!(flagVal ^ HEX_1))
		{
			m_tapeVirtualMachine.setFlagRegister(HEX_1);
			valSet = true;
		}
		break;
	case eGreaterThan:
		if(!(flagVal ^ HEX_2))
		{
			m_tapeVirtualMachine.setFlagRegister(HEX_1);
			valSet = true;
		}
		break;
	case eEquality:
		if(!(flagVal ^ HEX_3))
		{
			m_tapeVirtualMachine.setFlagRegister(HEX_1);
			valSet = true;
		}
		break;
	default:
		valSet = false;
		break;
	}

	if( !valSet )
	{
		m_tapeVirtualMachine.setFlagRegister(HEX_0);
	}
}

void Interpreter::IFBlock()
{
	if(eIF == m_lex.getCurrentToken())
	{
		++_ifCount;
	}
	else if(eFI == m_lex.getCurrentToken()) 
	{//No need to give this condition again but just gave to safe guard and see that only FI brings control here.
		--_ifCount;
		if(_ifCount < 0)
			printf("Mis-matched FI\n");
		return;
	}
	else
	{
		printf("Not IF block. Token mismatch somewhere\a\n");
		return;
	}

	if(eLeftParen == m_lex.getNextToken())
	{
		switch(m_lex.getNextToken())
		{
		case eLessThan:// \<
		case eGreaterThan:// \>
		case eEquality:// \=
			compareWithNextBoolean();
			if( (m_lex.getNextToken() == eRightParen) )
			{
				const ulong flagVal = m_tapeVirtualMachine.getFlagRegister();

				if( !(HEX_1 ^ flagVal) )
				{
					m_lex.getNextToken();
					enmTokens tok = m_lex.getCurrentToken();//shakti del tok
					ExecuteSentence();
					tok = m_lex.getCurrentToken();//shakti del tok
				}
				else/* if(HEX_1 & m_tapeVirtualMachine.getFlagRegister())*/
				{
					while( (m_lex.getNextToken() != eFI) && (m_lex.getCurrentToken() != eTokenOver) )
						;//NULL while to eat up all characters till we get ]. NULL Statement()
					if(m_lex.getCurrentToken() == eTokenOver)
						printf("Abrupt end, no FI found for IF\n");
				}
			}
			else
			{
				printf("IF condition not ending properly. \"IF(<cond>\" found, right paren missing\n");
			}
			break;
		default:
			//set error TODO
			break;
		}
	}
	else
	{
		//set error - TODO
	}
}

void Interpreter::compareWithNext()
{
	if(m_tapeVirtualMachine.getCurrentHeadValue() < m_tapeVirtualMachine.getNthPosValFrmHead(1))
	{
		m_tapeVirtualMachine.setFlagRegister(HEX_1);
	}
	else if(m_tapeVirtualMachine.getCurrentHeadValue() > m_tapeVirtualMachine.getNthPosValFrmHead(1))
	{
		m_tapeVirtualMachine.setFlagRegister(HEX_2);
	}
	else
	{
		m_tapeVirtualMachine.setFlagRegister(HEX_3);
	}
}

bool Interpreter::isBlankOrNull(const char* str)
{
	//For now only check string len, TODO check for blank too
	return (strlen(str) > 0)? false : true;
}

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License

This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)

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BrainlessLabs.com
Engineer
India India
I like to explore different aspects of technology. Try new things, and get delighted. My interests are programming language, and Imaging. But its not hard to work on other things also. Algorithms delight me over a coffee break.
 
I basically code in C++, but JAVA is not so alien for me. I know few scripting languages also. Basically I feel that knowing a programing language is just a matter of getting introduced to it.
 
For my other articles check my blog on homepage:
 
http://brainlesslabs.com/
 
https://github.com/BrainlessLabs
 
http://www.luxrender.net/en_GB/authors_contributors - SMISRA
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