Language Design

Design Language such as XML.

Define LEX

LEX define are accomplished, direct open XML.ddw file from sample folder. Click here to see the diagram.

Define Grammar

 

<--Syntax Start
<--Syntax Node Start
<--Syntax Node End
<--Syntax Node
<--Syntax Error
<--Syntax Identifier
<--Syntax Keyword
<--Syntax Number
<--Syntax Constant
<--Syntax Symbol
<--Syntax State

 

 

 

 

 

 

 

 

 

 

Grammar support LR(n). 'n' is unlimited. Double click Syntax Node/Identifier/Number/Constant/Symbol, see the property :

Check the Lookup Right combobox, then the analyzer will reads input 1 more derivation to right to decide grammar regular. Serial connections have 'Lookup Right 1' then can support LR(n),n is unlimited. For example, define C++ member function declear syntax:

string get_string();

The parser read 'string' identifier, it is a DataType or FunctionName ? Here can not decide. It must lookup right one more derivation 'get_string', then reading 'get_string' also can not decide it is a DataType + FunctionName. So that lookup right again, read '(' then decide it is Dfunction DataType + FunctionName+'('.

Parser Code generation

The generattion gererate LEX type enum from 'CCDefines.h', a parser code in 'LParser.cpp', sample project in 'main.cpp'.

How the parser work in LR(n)? See the key code generated by Duceland Designer :

bool LParser::Is_MemberFunction(LexWordList *words,int &index,LGrammarTree *tree)//MemberFunction {
    ...
    if(Is_DataType(words,index,this_tree))
    {
        index_1=index-1;
        lookup_right_pass=false;
        if(!lookup_right_pass)
        {
            index_1++;
            if((*words)[index_1]->Type==ltKeyword || (*words)[index_1]->Value==L"operator")
            lookup_right_pass=true;
            index_1--;
        }
        if(!lookup_right_pass)
        {
            index_1++;
            if((*words)[index_1]->Type==ltIdentifier)//function name
            {
                if(!lookup_right_pass)
                {
                    index_1++;
                    if((*words)[index_1]->Type==ltLeftBracket/*'('*/)
                    lookup_right_pass=true;
                    index_1--;
                }
                
            }
            index_1--;
        }
        if(!lookup_right_pass)
        {
            int local_old=index_1;
            index_1++;
            if(Is_decorate(words,index_1,NULL))
            {
                index_1--;
                if(!lookup_right_pass)
                {
                    index_1++;
                    if((*words)[index_1]->Type==ltIdentifier)//function name
                    {
                        if(!lookup_right_pass)
                        {
                            index_1++;
                            if((*words)[index_1]->Type==ltLeftBracket/*'('*/)
                            lookup_right_pass=true;
                            index_1--;
                        }
                        
                    }
                    index_1--;
                }
                
            }
            index_1=local_old;
        }
        
        if(lookup_right_pass)
        {
            if(tree)
            {
                tree->AddChild(this_tree);
            }
            
            current_word=(*words)[index];
            goto S_4EBA4D22972F43C8A0C0E78C946E5587;//DataType
        }
    }
    ...
}

The local varaint lookup_right_pass check lookup right passed. If look right 1 fail, reader position will be turn back(index_1--).

To learn more

See XML Parser sample