This article is from the GNU Chess and XBoard FAQ, by Tim Mann email@example.com with numerous contributions by others.
The file parser.c is automatically generated from parser.l. The Makefile
included with the WinBoard source kit has a rule for generating parser.c
using the program "flex", which will fail if you don't have flex.
However, the source kit also includes a ready-made copy of parser.c, so
you don't really need flex unless you have made changes to parser.l.
Check that you still have a copy of parser.c; if you don't, unpack the
WinBoard source zip file again to get one. Either set the last-modified
time of parser.c to be later than that of parser.l, or comment out the
Makefile rule for building parser.c from parser.l, and then try building
If you do want to change parser.l and rebuild parser.c, you can get flex
as part of the free Cygwin32 kit from www.cygnus.com. You can probably
also get flex for Windows by itself from various other places around the
Internet. It is free software distributed by the Free Software