constantp: fully expand; recognize functions.

This patch improves the constantp function dramatically.  It
now performs a full expansion of its argument, and recognizes
all of the constant foldable functions that the compiler
recognizes.

* eval.c (const_foldable_s): New symbol variable.
(const_foldable_hash): New static variable.
(constantp_noex): Look up function in the hash table of const
foldable functions, including in the case when it appears in a
dwim form as in [+ 2 2] which is (dwim + 2 2). In this case,
recursively check the arguments for constantp_noex.
We get the hash table of foldable functions from the
sys:%const-foldable% variable, which comes from an autoloaded
module.
(constantp): Fully expand the input form, not just m
macroexpand.
(eval_init): Register the const_foldable_s variable.

* lisplib.c (constfun_instantiate, constfun_set_entries): New
static functions.
(lisplib_init): Register auto-loading of constfun module
via new static functions.

* stdlib/compiler.tl; Load the constfun module if
%const-foldable% is not defined.
(%const-foldable-funs%, %const-foldable%): Removed from here.

* stdlib/constfun.tl: New file.
(%const-foldable-funs%, %const-foldable%): Moved here.

* txr.1: Documented changes to constantp.

1 files changed, 18 insertions, 0 deletions

diff --git a/lisplib.c b/lisplib.c
index 37b21ba0..a97f741f 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -936,6 +936,23 @@ static val pic_set_entries(val dlt, val fun)
   return nil;
 }
 
+static val constfun_instantiate(val set_fun)
+{
+  funcall1(set_fun, nil);
+  load(scat2(stdlib_path, lit("constfun")));
+  return nil;
+}
+
+static val constfun_set_entries(val dlt, val fun)
+{
+  val sys_name[] = {
+    lit("%const-foldable%"),
+    nil
+  };
+  set_dlt_entries_sys(dlt, sys_name, fun);
+  return nil;
+}
+
 val dlt_register(val dlt,
                  val (*instantiate)(val),
                  val (*set_entries)(val, val))
@@ -993,6 +1010,7 @@ void lisplib_init(void)
   dlt_register(dl_table, match_instantiate, match_set_entries);
   dlt_register(dl_table, doc_instantiate, doc_set_entries);
   dlt_register(dl_table, pic_instantiate, pic_set_entries);
+  dlt_register(dl_table, constfun_instantiate, constfun_set_entries);
 
   reg_fun(intern(lit("try-load"), system_package), func_n1(lisplib_try_load));
 }