From 0c5dec75a7c68ca69384bbc27f8a273976de92d1 Mon Sep 17 00:00:00 2001
From: Leah Neukirchen <leah@vuxu.org>
Date: Fri, 9 Dec 2022 17:51:21 +0100
Subject: add sgn

---
 mew.scm        | 6 +++++-
 mew.svnwiki    | 4 ++++
 tests/test.mew | 7 +++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/mew.scm b/mew.scm
index a6ac371..f95c0b1 100644
--- a/mew.scm
+++ b/mew.scm
@@ -18,7 +18,7 @@
      odometer one-of op op*
      per prn proj puts
      rand range rep
-     sample scan scan-right sing? search seq set set-at
+     sample scan scan-right sing? search seq set set-at sgn
      shuffle shuffle! str slurp
      tally-accumulator tbl time
      while
@@ -105,6 +105,10 @@
 
   (reexport err)
 
+  (define (sgn n)
+    (cond ((< n 0) -1)
+          ((> n 0)  1)
+          (else     0)))                ; always return an integer 0, not n
 
   (define (inc i)
     (+ i 1))
diff --git a/mew.svnwiki b/mew.svnwiki
index 29eb4e9..11a2669 100644
--- a/mew.svnwiki
+++ b/mew.svnwiki
@@ -152,6 +152,10 @@ Alias for {{floor-quotient}}.
 
 Alias for {{floor-remainder}}.
 
+<procedure>(sgn <num>)</procedure>
+
+Returns -1, 0, 1 depending on whether {{<num>}} is negative, zero, or positve.
+
 
 == General helpers
 
diff --git a/tests/test.mew b/tests/test.mew
index 1fe7ec1..72d1e27 100644
--- a/tests/test.mew
+++ b/tests/test.mew
@@ -83,6 +83,13 @@
   (test 5 (mod -16 7))
   (test -2 (mod -16 -7)))
 
+(test-group "sgn"
+  (test -1 (sgn -42))
+  (test 0 (sgn 0))
+  (test #t (eq? 0 (sgn 0.0)))
+  (test #t (eq? 0 (sgn -0.0)))
+  (test 1 (sgn 42)))
+
 (test-group "inc"
   (test 6 (inc 5))
   (test 0 (inc -1))
-- 
cgit 1.4.1