list-builder: dequeue capabilities with del/del* operators.

* lisplib.c (build_set_entries): Add buildn for autload, and
intern del and del* symbols.

* share/txr/stdlib/build.tl (list-builder): New methods del
and del*.
(sys:list-builder-flets): Generate flet for del*.
(sys:build-expander): New function, consisting of expansion
logic previously in build function. Macrolet added for del.
(build): Call sys:build-expander.
(buildn): New macro.

* txr.1: Documented.

1 files changed, 4 insertions, 2 deletions

diff --git a/lisplib.c b/lisplib.c
index a5116043..43c9e5d1 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -426,11 +426,13 @@ static val awk_instantiate(val set_fun)
 static val build_set_entries(val dlt, val fun)
 {
   val name[] = {
-    lit("list-builder"), lit("build-list"), lit("build"), nil
+    lit("list-builder"), lit("build-list"), lit("build"), lit("buildn"), nil
   };
   val name_noload[] = {
     lit("head"), lit("tail"), lit("add"), lit("add*"), lit("pend"),
-    lit("pend*"), lit("ncon"), lit("ncon*"), lit("get"), nil
+    lit("pend*"), lit("ncon"), lit("ncon*"), lit("get"),
+    lit("del"), lit("del*"),
+    nil
   };
 
   set_dlt_entries(dlt, name, fun);