add singul functionHEADmain

2 files changed, 10 insertions, 0 deletions

diff --git a/README.md b/README.md
index 82e1f02..886e4c6 100644
--- a/README.md
+++ b/README.md
@@ -186,6 +186,14 @@ atom(s), otherwise `f`:
     (consp t)                 ; f
     (consp '(a b))            ; t
 
+`(singul x)` returns `t` if `x` is either an empty list `()`, or an atom,
+otherwise `f`:
+
+    (singul ())               ; t
+    (singul +1)               ; t
+    (singul t)                ; t
+    (singul '(a b))           ; f
+
 `(zerop x)` returns `t` if `x` is the number zero, otherwise `f`:
 
     (zerop +0)                ; t
diff --git a/liblali.c b/liblali.c
index cadd9e1..af3f108 100644
--- a/liblali.c
+++ b/liblali.c
@@ -1664,6 +1664,8 @@ static char *stdlib = LISP(
 
   (defun consp (x) (and (listp x) (algo x)))
 
+  (defun singul (x) (not (consp x)))
+
   (defun differ (x y)
     (fill ((and (consp x) (consp y)) (dif x y))
           (f (or (differ (car x) (car y))