4 files changed, 54 insertions, 1 deletions

diff --git a/src/scheme/ao_scheme.h b/src/scheme/ao_scheme.h
index 4655b2a9..2fa1ed60 100644
--- a/src/scheme/ao_scheme.h
+++ b/src/scheme/ao_scheme.h
@@ -634,6 +634,9 @@ ao_scheme_cons_display(ao_poly);
 int
 ao_scheme_cons_length(struct ao_scheme_cons *cons);
 
+struct ao_scheme_cons *
+ao_scheme_cons_copy(struct ao_scheme_cons *cons);
+
 /* string */
 extern const struct ao_scheme_type ao_scheme_string_type;
 
diff --git a/src/scheme/ao_scheme_builtin.c b/src/scheme/ao_scheme_builtin.c
index 397ce032..6f9e1390 100644
--- a/src/scheme/ao_scheme_builtin.c
+++ b/src/scheme/ao_scheme_builtin.c
@@ -198,6 +198,19 @@ ao_scheme_do_length(struct ao_scheme_cons *cons)
 }
 
 ao_poly
+ao_scheme_do_list_copy(struct ao_scheme_cons *cons)
+{
+	struct ao_scheme_cons *new;
+
+	if (!ao_scheme_check_argc(_ao_scheme_atom_length, cons, 1, 1))
+		return AO_SCHEME_NIL;
+	if (!ao_scheme_check_argt(_ao_scheme_atom_length, cons, 0, AO_SCHEME_CONS, 1))
+		return AO_SCHEME_NIL;
+	new = ao_scheme_cons_copy(ao_scheme_poly_cons(ao_scheme_arg(cons, 0)));
+	return ao_scheme_cons_poly(new);
+}
+
+ao_poly
 ao_scheme_do_quote(struct ao_scheme_cons *cons)
 {
 	if (!ao_scheme_check_argc(_ao_scheme_atom_quote, cons, 1, 1))
diff --git a/src/scheme/ao_scheme_builtin.txt b/src/scheme/ao_scheme_builtin.txt
index b7261ce1..17f5ea0c 100644
--- a/src/scheme/ao_scheme_builtin.txt
+++ b/src/scheme/ao_scheme_builtin.txt
@@ -8,6 +8,7 @@ f_lambda	cdr
 f_lambda	cons
 f_lambda	last
 f_lambda	length
+f_lambda	list_copy	list-copy
 nlambda		quote
 atom		quasiquote
 atom		unquote
diff --git a/src/scheme/ao_scheme_cons.c b/src/scheme/ao_scheme_cons.c
index 21ee10cc..02512e15 100644
--- a/src/scheme/ao_scheme_cons.c
+++ b/src/scheme/ao_scheme_cons.c
@@ -112,7 +112,7 @@ ao_scheme_cons_cdr(struct ao_scheme_cons *cons)
 	if (cdr == AO_SCHEME_NIL)
 		return NULL;
 	if (ao_scheme_poly_type(cdr) != AO_SCHEME_CONS) {
-		(void) ao_scheme_error(AO_SCHEME_INVALID, "improper list");
+		(void) ao_scheme_error(AO_SCHEME_INVALID, "improper cdr %v", cdr);
 		return NULL;
 	}
 	return ao_scheme_poly_cons(cdr);
@@ -124,6 +124,42 @@ ao_scheme__cons(ao_poly car, ao_poly cdr)
 	return ao_scheme_cons_poly(ao_scheme_cons_cons(car, cdr));
 }
 
+struct ao_scheme_cons *
+ao_scheme_cons_copy(struct ao_scheme_cons *cons)
+{
+	struct ao_scheme_cons	*head = NULL;
+	struct ao_scheme_cons	*tail = NULL;
+
+	while (cons) {
+		struct ao_scheme_cons	*new;
+		ao_poly cdr;
+
+		ao_scheme_cons_stash(0, cons);
+		ao_scheme_cons_stash(1, head);
+		ao_scheme_poly_stash(0, ao_scheme_cons_poly(tail));
+		new = ao_scheme_alloc(sizeof (struct ao_scheme_cons));
+		cons = ao_scheme_cons_fetch(0);
+		head = ao_scheme_cons_fetch(1);
+		tail = ao_scheme_poly_cons(ao_scheme_poly_fetch(0));
+		if (!new)
+			return AO_SCHEME_NIL;
+		new->car = cons->car;
+		new->cdr = AO_SCHEME_NIL;
+		if (!head)
+			head = new;
+		else
+			tail->cdr = ao_scheme_cons_poly(new);
+		tail = new;
+		cdr = cons->cdr;
+		if (ao_scheme_poly_type(cdr) != AO_SCHEME_CONS) {
+			tail->cdr = cdr;
+			break;
+		}
+		cons = ao_scheme_poly_cons(cdr);
+	}
+	return head;
+}
+
 void
 ao_scheme_cons_free(struct ao_scheme_cons *cons)
 {