* configure.ac: Output src/ltlenv/Makefile.

* src/ltlenv/Makefile.am, src/ltlenv/defaultenv.cc,
src/ltlenv/defaultenv.hh, src/ltlenv/environment.hh: New files.
* src/ltlparse/public.hh (parse): Take an environment as third
argument.
* src/ltlparse/ltlparse.yy (ATOMIC_PROP, parse): Require the
atomic proposition via the environment.
* src/ltltest/readltl.cc (main): Adjust the call to parse().
* src/ltltest/Makefile.am (LDADD): Add ../ltlenv/libltlenv.a.

src/ltlparse/public.hh

@@ -1,9 +1,10 @@
 #ifndef SPOT_LTLPARSE_PUBLIC_HH
 # define SPOT_LTLPARSE_PUBLIC_HH
 
-# include <string>
 # include "ltlast/formula.hh"
 # include "location.hh"
+# include "ltlenv/defaultenv.hh"
+# include <string>
 # include <list>
 # include <utility>
 # include <iostream>
@@ -17,8 +18,9 @@ namespace spot
 
     // Beware: this function is *not* reentrant.
     formula* parse(const std::string& ltl_string, 
-		    parse_error_list& error_list,
-		    bool debug = false);
+		   parse_error_list& error_list,
+		   environment& env = default_environment::instance(),
+		   bool debug = false);
 
     // Return true iff any diagnostic was output to os.
     bool format_parse_errors(std::ostream& os,