From bc85ec12271ecc273cb36e7ef35d071c364e46ab Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 16 Nov 2015 06:45:13 -0800
Subject: Provide butlast function.

* eval.c (eval_init): Registered butlast intrinsic.

* lib.c (butlast): New function.

* lib.h (butlast): Declared.

* txr.1: Documented butlast.
---
 eval.c |  1 +
 lib.c  |  5 +++++
 lib.h  |  1 +
 txr.1  | 24 ++++++++++++++++++++++++
 4 files changed, 31 insertions(+)

diff --git a/eval.c b/eval.c
index fd5a720f..b1bb0d17 100644
--- a/eval.c
+++ b/eval.c
@@ -4471,6 +4471,7 @@ void eval_init(void)
   reg_fun(intern(lit("reverse"), user_package), func_n1(reverse));
   reg_fun(intern(lit("ldiff"), user_package), func_n2(ldiff));
   reg_fun(intern(lit("last"), user_package), func_n1(last));
+  reg_fun(intern(lit("butlast"), user_package), func_n1(butlast));
   reg_fun(intern(lit("nthcdr"), user_package), func_n2(nthcdr));
   reg_fun(intern(lit("flatten"), user_package), func_n1(flatten));
   reg_fun(intern(lit("flatten*"), user_package), func_n1(lazy_flatten));
diff --git a/lib.c b/lib.c
index 09e85693..580b2c2c 100644
--- a/lib.c
+++ b/lib.c
@@ -7396,6 +7396,11 @@ val dwim_del(val seq, val ind_range)
   }
 }
 
+val butlast(val seq)
+{
+  return sub(seq, zero, negone);
+}
+
 val update(val seq, val fun)
 {
   switch (type(seq)) {
diff --git a/lib.h b/lib.h
index 153492d9..3b10ce6d 100644
--- a/lib.h
+++ b/lib.h
@@ -905,6 +905,7 @@ val ref(val seq, val ind);
 val refset(val seq, val ind, val newval);
 val dwim_set(val seq, val ind_range, val newval);
 val dwim_del(val seq, val ind_range);
+val butlast(val seq);
 val replace(val seq, val items, val from, val to);
 val update(val seq, val fun);
 val search(val seq, val key, val from, val to);
diff --git a/txr.1 b/txr.1
index 281bc167..dbb819d9 100644
--- a/txr.1
+++ b/txr.1
@@ -20103,6 +20103,30 @@ is returned, which may be
 .meta sequence
 itself or a copy.
 
+.coNP Function @ butlast
+.synb
+.mets (butlast << sequence )
+.syne
+.desc
+The
+.code butlast
+function returns the prefix of
+.meta sequence
+consisting of a copy of it, with the last item omitted.
+If
+.meta sequence
+is empty, an empty sequence is returned.
+
+Dialect note: the Common Lisp function
+.code nbutlast
+is not provided. The \*(TL
+.code take
+function provides the same functionality for lists (only with the
+arguments reversed relative to
+.codn nbutlast ),
+and additionally provides lazy semantics, and works with vectors
+and strings.
+
 .coNP Function @ search
 .synb
 .mets (search < haystack < needle >> [ testfun <> [ keyfun ])
-- 
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