From: Keith Packard <keithp@keithp.com>
Date: Thu, 4 Jan 2018 10:25:45 +0000 (-0800)
Subject: altos/scheme: Add builtin list-tail
X-Git-Tag: 1.8.5~1^2~2^2~22
X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=a6e01e7aafb1d1fdb15d633ec23d8fe51afd15df;p=fw%2Faltos

altos/scheme: Add builtin list-tail

This is used enough to warrant a builtin, rather than lisp implementation

Signed-off-by: Keith Packard <keithp@keithp.com>
---

diff --git a/src/scheme/ao_scheme_builtin.c b/src/scheme/ao_scheme_builtin.c
index 0b84a89a..1bfe6942 100644
--- a/src/scheme/ao_scheme_builtin.c
+++ b/src/scheme/ao_scheme_builtin.c
@@ -230,6 +230,31 @@ ao_scheme_do_list_copy(struct ao_scheme_cons *cons)
 	return ao_scheme_cons_poly(new);
 }
 
+ao_poly
+ao_scheme_do_list_tail(struct ao_scheme_cons *cons)
+{
+	ao_poly	list;
+	int32_t	v;
+
+	if (!ao_scheme_check_argc(_ao_scheme_atom_list2dtail, cons, 2, 2))
+		return AO_SCHEME_NIL;
+	if (!ao_scheme_check_argt(_ao_scheme_atom_list2dtail, cons, 0, AO_SCHEME_CONS, 1))
+		return AO_SCHEME_NIL;
+	list = ao_scheme_arg(cons, 0);
+	v = ao_scheme_arg_int(_ao_scheme_atom_list2dtail, cons, 1);
+	if (ao_scheme_exception)
+		return AO_SCHEME_NIL;
+	while (v > 0) {
+		if (!list)
+			return ao_scheme_error(AO_SCHEME_INVALID, "%v: ran off end", _ao_scheme_atom_list2dtail);
+		if (!ao_scheme_is_cons(list))
+			return ao_scheme_error(AO_SCHEME_INVALID, "%v: invalid list", _ao_scheme_atom_list2dtail);
+		list = ao_scheme_poly_cons(list)->cdr;
+		v--;
+	}
+	return list;
+}
+
 ao_poly
 ao_scheme_do_quote(struct ao_scheme_cons *cons)
 {
diff --git a/src/scheme/ao_scheme_builtin.txt b/src/scheme/ao_scheme_builtin.txt
index 4739f121..7298add7 100644
--- a/src/scheme/ao_scheme_builtin.txt
+++ b/src/scheme/ao_scheme_builtin.txt
@@ -12,6 +12,7 @@ all	f_lambda	cons
 all	f_lambda	last
 all	f_lambda	length
 all	f_lambda	list_copy	list-copy
+all	f_lambda	list_tail	list-tail
 all	nlambda		quote
 QUASI	atom		quasiquote
 QUASI	atom		unquote