Re: Context sensitive scanner ?

// GRAMMAR BEGINS


/*


This simple Visual Parse++ grammar demonstrates a reply
to the following question, posted in comp.compilers by
a.hofkamp@wtb.tue.nl:


>We are busy writing a language where the following
>constructs occur:


> 1) Literal reals (such as 1.2),
> 2) Nested index operations on arrays (such as x.1.2).


[...]


> Since the scanner is not context-sensitive, it
> does not understand that the second expression
> should be returned as IDEN x, DOT, NUM 1, DOT NUM 2


> I am aware of the capability of creating states in
> Lex, but I do not really like it, since it heavily
> depends on the exact moment of executing
> when YACC statements (at the end of a rule).


The parse tree generated by the following data stream:


x.1.2 1.2


can be seen at:


http://mypage.direct.ca/q/qjackson/x12parse_tree.gif


*/


%macro


{dot} '\.';
{id} '[a-zA-Z_][a-zA-Z0-9_]*';
{ws} '[ \t\n]+';
{digit} '[0-9]';


%expression main


'.' %ignore; // for this demo we ignore this
'{ws}' %ignore; // for this demo we ignore this


'{id}{dot}'
ArrayDescriptor, 'x.', %push InArray;


'{digit}+'
Integer, 'INT';


'{digit}+{dot}{digit}*'
Real, 'REAL';


%expression InArray


'.' %ignore, %pop;
'{ws}' %ignore, %pop;


'{dot}' ArraySubscriptOperator, 'ARRAY_DOT';


'{digit}+'
Index, 'INDEX';


%production S


Lambda lambda -> ;


S_00 S -> lambda;
S_01 S -> particle S;


ParticleReal particle -> real;
ParticleArray particle -> array;


RealNumber real -> 'REAL';


Array array -> 'x.' index;


IndexSimple index -> 'INDEX';
IndexCompound index -> 'INDEX' 'ARRAY_DOT' index;


// GRAMMAR ENDS




--
Quinn Tyler Jackson -- "The Artful Parser"


email: qjackson@direct.ca
url: http://mypage.direct.ca/q/qjackson/
--

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