[fpc-devel] Patch for lexlib

[Felipe Monteiro de Carvalho]

Hello,

I am writing scanners using plex, and I found a problem with the
current lexlib. It has a function called yywrap which will close the
input and the output, and there is no way to prevent that. I would
like to parse the same file several times, and simply closing the
file, reopening it and reseting it somehow doesn't work. It soon
crashes. If I prevent yywrap from closing the file (only possible
changing lexlib), then everything works good.

I searched how people solve this in C, and there there is some
pre-processor magic which allows them declare their own yywrap
function. All yywrap declarations I saw in my search would just return
true, so I added a variable called yycloseiowhendone, which is
initially true and when set to false will do what everyone wants when
redeclaring yywrap: Just return true

Please review the following patch. Existing applications shouldn't be
affected by it. If accepted, I'll apply it to trunk, thanks.

Index: h2pas/lexlib.pas
===================================================================
--- h2pas/lexlib.pas	(revision 10497)
+++ h2pas/lexlib.pas	(working copy)
@@ -45,6 +45,8 @@
 yytext            : String;      (* matched text (should be considered r/o) *)
 yyleng            : Byte         (* length of matched text *)
   absolute yytext;
+yycloseiowhendone : Boolean;     (* Identifies if yyinput and yyoutput
+                                    shall be closed when yylex ends *)

 (* I/O routines:

@@ -307,7 +309,11 @@

 function yywrap : Boolean;
   begin
-    close(yyinput); close(yyoutput);
+    if yycloseiowhendone then
+    begin
+      close(yyinput);
+      close(yyoutput);
+    end;
     yywrap := true;
   end(*yywrap*);

@@ -401,6 +407,7 @@
   end(*yyclear*);

 begin
+  yycloseiowhendone := True;
   assign(yyinput, '');
   assign(yyoutput, '');
   reset(yyinput);