Completion of fallback list implementation.

* lib.c (find_symbol): New function.
(symbol_present): Search the fallback list also to
determine whether the symbol is visible.

* lib.h (find_symbol): Declared.

* parser.y (sym_helper): Implement a new behavior for
qualified symbols. Interning new symbols is only allowed
for packages that have an empty fallback list.

* parser.c (get_visible_syms): New static function.
(find_matching_syms): Use get_visible_syms to get
the list of eligible symbols. This way the fallback list
of the package is included if it is the current package.

* share/txr/stdlib/package.tl (defpackage): Do not insert
a default (:use usr) if there is no :usr clause. Since
defpackage is very new, no need for backward compatibility;
the amount of code depending on this is likely zero.

* txr.1: Documented fallback list feature.

1 files changed, 16 insertions, 2 deletions

diff --git a/parser.y b/parser.y
index e26214a4..8d3e5a89 100644
--- a/parser.y
+++ b/parser.y
@@ -1278,10 +1278,24 @@ static val sym_helper(parser_t *parser, wchar_t *lexeme, val meta_allowed)
     } else {
       val package = find_package(pkg_name);
       if (!package) {
-        yyerrorf(scnr, lit("~a:~a: package ~a not found"), pkg_name, sym_name, pkg_name, nao);
+        yyerrorf(scnr, lit("~a:~a: package ~a not found"),
+                 pkg_name, sym_name, pkg_name, nao);
         return nil;
       }
-      sym = intern(sym_name, package);
+
+      sym = find_symbol(sym_name, package);
+
+      if (sym == zero) {
+        if (!package_fallback_list(package)) {
+          sym = intern(sym_name, package);
+        } else {
+          yyerrorf(scnr, lit("~a:~a: cannot intern symbol using qualified symbol syntax,"),
+                   pkg_name, sym_name, nao);
+          yyerrorf(scnr, lit("~a:~a: because package ~a has a fallback list"),
+                   pkg_name, sym_name, pkg_name, nao);
+          return nil;
+        }
+      }
     }
   } else {
     val sym_name = string(lexeme);