Adding promisep function.

* eval.c (promisep): New static function.
(eval_init): Registered promisep intrinsic.

* txr.1: Documented promisep.

2 files changed, 33 insertions, 0 deletions

diff --git a/eval.c b/eval.c
index fa8a8757..7c5da0be 100644
--- a/eval.c
+++ b/eval.c
@@ -3786,6 +3786,17 @@ static val weavev(struct args *args)
   return lazy_appendl(generate(whil, gen));
 }
 
+static val promisep(val obj)
+{
+  if (consp(obj)) {
+    val sym = car(obj);
+    if (sym == promise_s || sym == promise_forced_s)
+      return t;
+  }
+
+  return nil;
+}
+
 static val force(val promise)
 {
   loc pstate = car_l(promise);
@@ -4692,6 +4703,7 @@ void eval_init(void)
   reg_fun(intern(lit("pad"), user_package), func_n3o(pad, 1));
   reg_fun(intern(lit("weave"), user_package), func_n0v(weavev));
   reg_fun(force_s, func_n1(force));
+  reg_fun(intern(lit("promisep"), user_package), func_n1(promisep));
   reg_fun(intern(lit("rperm"), user_package), func_n2(rperm));
   reg_fun(intern(lit("perm"), user_package), func_n2o(perm, 1));
   reg_fun(intern(lit("comb"), user_package), func_n2(comb));
diff --git a/txr.1 b/txr.1
index 6e612436..9b6d6490 100644
--- a/txr.1
+++ b/txr.1
@@ -15624,6 +15624,27 @@ the promise will take on the value of
 .meta expression
 or the assigned value.
 
+.coNP Function @ promisep
+.synb
+.mets (promisep << object )
+.syne
+.desc
+The
+.code promisep
+function returns
+.code t
+if
+.meta object
+is a promise object: an object created by the
+.code delay
+macro.  Otherwise it returns
+.codn nil .
+
+Note: promise objects are conses. The
+.code typeof
+function applied to a promise returns
+.codn cons .
+
 .coNP Macro @ mlet
 .synb
 .mets (mlet >> ({ sym | >> ( sym << init-form )}*) << body-form *)