New function: endp.

This improves compatibility with other Lisp dialects
in a small way.

* eval.c (eval_init): Register endp intrinsic.

* lib.c (endp): New function.

* lib.h (endp): Declared.

* txr.1: Documented endp.

4 files changed, 37 insertions, 0 deletions

diff --git a/eval.c b/eval.c
index a5888e9f..5b7065e4 100644
--- a/eval.c
+++ b/eval.c
@@ -5139,6 +5139,7 @@ void eval_init(void)
   reg_fun(intern(lit("consp"), user_package), func_n1(consp));
   reg_fun(intern(lit("lconsp"), user_package), func_n1(lconsp));
   reg_fun(intern(lit("listp"), user_package), func_n1(listp));
+  reg_fun(intern(lit("endp"), user_package), func_n1(endp));
   {
     val proper_list_p_f = func_n1(proper_list_p);
     reg_fun(intern(lit("proper-listp"), user_package), proper_list_p_f);
diff --git a/lib.c b/lib.c
index 1ca1790c..6576049c 100644
--- a/lib.c
+++ b/lib.c
@@ -2758,6 +2758,16 @@ val listp(val obj)
   return if2(obj == nil || consp(obj), t);
 }
 
+val endp(val obj)
+{
+  if (obj == nil)
+    return t;
+  if (consp(obj))
+    return nil;
+  uw_throwf(error_s, lit("endp: list improperly terminated by ~s"),
+            obj, nao);
+}
+
 val proper_list_p(val obj)
 {
   while (consp(obj))
diff --git a/lib.h b/lib.h
index 4a4e52a4..3ebc5c22 100644
--- a/lib.h
+++ b/lib.h
@@ -606,6 +606,7 @@ val consp(val obj);
 val lconsp(val obj);
 val atom(val obj);
 val listp(val obj);
+val endp(val obj);
 val proper_list_p(val obj);
 val length_list(val list);
 val getplist(val list, val key);
diff --git a/txr.1 b/txr.1
index ca74fe48..549a7da3 100644
--- a/txr.1
+++ b/txr.1
@@ -17046,6 +17046,31 @@ installations should use
 .codn proper-listp ,
 but its use going forward is deprecated.
 
+.coNP Function @ endp
+.synb
+.mets (endp << object )
+.syne
+.desc
+The
+.code endp
+function returns
+.code t
+if
+.meta object
+is the object
+.codn nil .
+
+If
+.meta object
+is a cons cell, then
+.code endp
+returns
+.codn t .
+
+Otherwise,
+.code endp
+function throws an exception.
+
 .coNP Function @ length-list
 .synb
 .mets (length-list << list )