From 5e79d95159a6cd680d045314fe427b263e7ab344 Mon Sep 17 00:00:00 2001
From: Leah Neukirchen <leah@vuxu.org>
Date: Mon, 2 Jan 2023 19:10:02 +0100
Subject: add push!, pop!

---
 mew.scm        | 22 +++++++++++++++++++++-
 mew.svnwiki    | 13 +++++++++++--
 tests/test.mew |  8 ++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/mew.scm b/mew.scm
index 845a16e..f170273 100644
--- a/mew.scm
+++ b/mew.scm
@@ -16,7 +16,7 @@
      mod
      negate nth-accumulator
      odometer one-of op op*
-     per prn proj puts
+     per pop! prn proj push! puts
      rand range rep
      sample scan scan-right sing? search seq set set-at sgn
      shuffle shuffle! str slurp
@@ -1077,6 +1077,26 @@
       ((_ location n)
        (set location (- location n)))))
 
+  (define-syntax push!
+    (syntax-rules ()
+      ((_ location x)
+       (set location (cons x location)))))
+
+  (define-syntax pop!
+    (syntax-rules ()
+      ((_ location)
+       (if (null? location)
+         (error "pop from empty list")
+         (let ((r (car location)))
+           (set! location (cdr location))
+           r)))
+      ((_ location default)
+       (if (null? location)
+         default
+         (let ((r (car location)))
+           (set! location (cdr location))
+           r)))))
+
   (define (and=> x . fs)
     (and x
          (if (null? fs)
diff --git a/mew.svnwiki b/mew.svnwiki
index 16dd90d..92ed78d 100644
--- a/mew.svnwiki
+++ b/mew.svnwiki
@@ -144,8 +144,8 @@ with a {{'message}} of {{<message>}} passed through {{format}} with
 
 Increment or decrement the argument by 1.
 
-<procedure>(inc! <loc> [<n>])</procedure>
-<procedure>(dec! <loc> [<n>])</procedure>
+<syntax>(inc! <loc> [<n>])</syntax>
+<syntax>(dec! <loc> [<n>])</syntax>
 
 Increment or decrement the location {{<loc>}} by {{<n>}} (default: 1).
 
@@ -302,6 +302,15 @@ Material implication: evaluate {{<antecedent>...}} until one is false,
 then shortcut and return true.  If all {{<antecedent>...}} are true,
 evaluate {{<consequent>}}.
 
+<syntax>(push! <loc> <val>)</syntax>
+
+Prepend {{<val>}} to the list stored at {{<loc>}}.
+
+<syntax>(pop! <loc> [<val>])</syntax>
+
+Return the head of {{<loc>}} and replace {{<loc>}} with its tail.
+If {{<loc>}} is empty, return {{<val>}} if given; else throw an exception.
+
 
 == I/O helpers
 
diff --git a/tests/test.mew b/tests/test.mew
index 44fdb95..d2eacbd 100644
--- a/tests/test.mew
+++ b/tests/test.mew
@@ -114,6 +114,14 @@
   (test 5 (loc (x 6) (dec! x)))
   (test 5 (loc (x 7) (dec! x 2))))
 
+(test-group "push!"
+  (test '(3 2 1) (loc (l '()) (push! l 1) (push! l 2) (push! l 3) l)))
+
+(test-group "pop!"
+  (test 1 (loc (l '(3 2 1)) (pop! l) (pop! l) (pop! l)))
+  (test-error (loc (l '(2 1)) (pop! l) (pop! l) (pop! l)))
+  (test 'foo (loc (l '(2 1)) (pop! l) (pop! l) (pop! l 'foo))))
+
 (test-group "boolean"
   (test #f (boolean #f))
   (test #t (boolean #t))
-- 
cgit 1.4.1