macros.l

/* the "incl" state is used for picking up the name
 * of an include file
 */
%x incl

%{
#define MAX_INCLUDE_DEPTH 10
YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH];
int include_stack_ptr = 0;
%}
%option prefix="foo"

%%
include             BEGIN(incl);

[a-z]+              ECHO;
[^a-z\n]*\n?        ECHO;

<incl>[ \t]*      /* eat the whitespace */
<incl>[^ \t\n]+   { /* got the include file name */
        if ( include_stack_ptr >= MAX_INCLUDE_DEPTH )
            {
            fprintf( stderr, "Includes nested too deeply" );
            exit( 1 );
            }

        include_stack[include_stack_ptr++] =
            YY_CURRENT_BUFFER;

        yyin = fopen( yytext, "r" );

        if ( ! yyin )
            error( ... );

        yy_switch_to_buffer(
            yy_create_buffer( yyin, YY_BUF_SIZE ) );

        BEGIN(INITIAL);
        }

<<EOF>> {
        if ( --include_stack_ptr < 0 )
            {
            yyterminate();
            }

        else
            {
            yy_delete_buffer( YY_CURRENT_BUFFER );
            yy_switch_to_buffer(
                 include_stack[include_stack_ptr] );
            }
        }