From 93d0ba9844dbba55658ce9c0d8570e294bd096b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 10 Apr 2023 22:02:44 +0200
Subject: Add init+last.

---
 doc/ref/guile/util.texi |  5 +++++
 module/hnh/util.scm     | 14 ++++++++++++--
 tests/test/hnh-util.scm |  3 +++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/doc/ref/guile/util.texi b/doc/ref/guile/util.texi
index 32e7543f..f60e2059 100644
--- a/doc/ref/guile/util.texi
+++ b/doc/ref/guile/util.texi
@@ -113,6 +113,11 @@ See @var{find-extreme}
 @end lisp
 @end defun
 
+@defun init+last list
+Returns two values: everything except the last element of @var{list},
+and the last element of @var{list}.
+@end defun
+
 @defun take-to lst n
 Equivalent to @var{take}, but return everything (instead of crash) if
 n > (length lst).
diff --git a/module/hnh/util.scm b/module/hnh/util.scm
index 759cdd48..c88a029e 100644
--- a/module/hnh/util.scm
+++ b/module/hnh/util.scm
@@ -17,6 +17,7 @@
            find-extreme find-min find-max
            filter-sorted
            !=
+           init+last
            take-to
            string-take-to
            string-first
@@ -150,9 +151,12 @@
 
 
 
+;; TODO this is called flip in Haskell land
 (define (swap f)
   (lambda args (apply f (reverse args))))
-
+;; Swap would be
+;; (define (swap p)
+;;   (xcons (car p) (cdr p)))
 
 ;; Allow set to work on multiple values at once,
 ;; similar to Common Lisp's @var{setf}
@@ -253,6 +257,12 @@
 ;; (define (!= a b) (not (= a b)))
 (define != (negate =))
 
+
+(define (init+last l)
+  (let ((last rest (car+cdr (reverse l))))
+    (values (reverse rest) last)))
+
+
 (define (take-to lst i)
   "Like @var{take}, but might lists shorter than length."
   (if (> i (length lst))
@@ -396,7 +406,7 @@
                       (reverse (cons (map list last) rest ))))))
 
 ;; Given an arbitary tree, do a pre-order traversal, appending all strings.
-;; non-strings allso allowed, converted to strings and also appended.
+;; non-strings also allowed, converted to strings and also appended.
 (define (string-flatten tree)
   (cond [(string? tree) tree]
         [(list? tree) (string-concatenate (map string-flatten tree))]
diff --git a/tests/test/hnh-util.scm b/tests/test/hnh-util.scm
index dc64a3aa..4e50ac1b 100644
--- a/tests/test/hnh-util.scm
+++ b/tests/test/hnh-util.scm
@@ -202,6 +202,9 @@
  (test-assert "not equal"
    (!= 1 2)))
 
+(test-group "init+last"
+  'TODO)
+
 (test-group "take-to"
  (test-equal "Take to"
    '() (take-to '() 5)))
-- 
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