sequence: implement (slice)

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

5 files changed, 78 insertions, 1 deletions

diff --git a/doc/language.txt b/doc/language.txt
index 7c67921..0fe760d 100644
--- a/doc/language.txt
+++ b/doc/language.txt
@@ -89,7 +89,7 @@
 
 (reverse sequence)
 
-IMPL: (slice from to sequence)
+(slice sequence from to)
 
 (position item sequence)
 
diff --git a/include/sheep/object_types.h b/include/sheep/object_types.h
index c2d4a9e..b9128a1 100644
--- a/include/sheep/object_types.h
+++ b/include/sheep/object_types.h
@@ -21,6 +21,7 @@ struct sheep_sequence {
 	sheep_t (*concat)(struct sheep_vm *, sheep_t, unsigned int);
 	sheep_t (*reverse)(struct sheep_vm *, sheep_t);
 	sheep_t (*nth)(struct sheep_vm *, size_t, sheep_t);
+	sheep_t (*slice)(struct sheep_vm *, sheep_t, size_t, size_t);
 	sheep_t (*position)(struct sheep_vm *, sheep_t, sheep_t);
 };
 
diff --git a/sheep/list.c b/sheep/list.c
index eea3026..bc9dc94 100644
--- a/sheep/list.c
+++ b/sheep/list.c
@@ -173,6 +173,42 @@ static sheep_t list_nth(struct sheep_vm *vm, size_t n, sheep_t sheep)
 	return sheep;
 }
 
+static sheep_t list_slice(struct sheep_vm *vm, sheep_t sheep,
+			size_t from, size_t to)
+{
+	struct sheep_list *list, *pos;
+	sheep_t new, result = NULL;
+	size_t index = 0;
+
+	sheep_protect(vm, sheep);
+
+	new = sheep_make_cons(vm, NULL, NULL);
+	sheep_protect(vm, new);
+
+	list = sheep_list(sheep);
+	pos = sheep_list(new);
+
+	while (index < to && list->head) {
+		if (index >= from) {
+			pos->head = list->head;
+			pos->tail = sheep_make_cons(vm, NULL, NULL);
+			pos = sheep_list(pos->tail);
+		}
+		list = sheep_list(list->tail);
+		index++;
+
+	}
+	if (index == to)
+		result = new;
+	else
+		sheep_error(vm, "index %ld out of range [0, %ld)", to, index);
+
+	sheep_unprotect(vm, new);
+	sheep_unprotect(vm, sheep);
+
+	return result;
+}
+
 static sheep_t list_position(struct sheep_vm *vm, sheep_t item, sheep_t sheep)
 {
 	struct sheep_list *list;
@@ -194,6 +230,7 @@ static const struct sheep_sequence list_sequence = {
 	.concat = list_concat,
 	.reverse = list_reverse,
 	.nth = list_nth,
+	.slice = list_slice,
 	.position = list_position,
 };
 
diff --git a/sheep/sequence.c b/sheep/sequence.c
index 2fea5dc..b4db341 100644
--- a/sheep/sequence.c
+++ b/sheep/sequence.c
@@ -64,6 +64,23 @@ static sheep_t builtin_nth(struct sheep_vm *vm, unsigned int nr_args)
 	return sheep_sequence(seq)->nth(vm, n, seq);
 }
 
+/* (slice sequence from to) */
+static sheep_t builtin_slice(struct sheep_vm *vm, unsigned int nr_args)
+{
+	long from, to;
+	sheep_t seq;
+
+	if (sheep_unpack_stack(vm, nr_args, "qNN", &seq, &from, &to))
+		return NULL;
+
+	if (from < 0 || to <= from) {
+		sheep_error(vm, "invalid range [%ld, %ld)", from, to);
+		return NULL;
+	}
+
+	return sheep_sequence(seq)->slice(vm, seq, from, to);
+}
+
 /* (position item sequence) */
 static sheep_t builtin_position(struct sheep_vm *vm, unsigned int nr_args)
 {
@@ -81,5 +98,6 @@ void sheep_sequence_builtins(struct sheep_vm *vm)
 	sheep_vm_function(vm, "concat", builtin_concat);
 	sheep_vm_function(vm, "reverse", builtin_reverse);
 	sheep_vm_function(vm, "nth", builtin_nth);
+	sheep_vm_function(vm, "slice", builtin_slice);
 	sheep_vm_function(vm, "position", builtin_position);
 }
diff --git a/sheep/string.c b/sheep/string.c
index 5d61e2c..9766042 100644
--- a/sheep/string.c
+++ b/sheep/string.c
@@ -111,6 +111,26 @@ static sheep_t string_nth(struct sheep_vm *vm, size_t n, sheep_t sheep)
 	return __sheep_make_string(vm, new, 1);
 }
 
+static sheep_t string_slice(struct sheep_vm *vm, sheep_t sheep,
+			size_t from, size_t to)
+{
+	struct sheep_string *string;
+	size_t length = 0;
+	char *new;
+
+	string = sheep_string(sheep);
+	if (to > string->nr_bytes) {
+		sheep_error(vm, "index %ld out of range [0, %ld)",
+			to, string->nr_bytes);
+		return NULL;
+	}
+	length = to - from;
+	new = sheep_malloc(length + 1);
+	memcpy(new, string->bytes + from, length);
+	new[length] = 0;
+	return __sheep_make_string(vm, new, length);
+}
+
 static sheep_t string_position(struct sheep_vm *vm, sheep_t item, sheep_t sheep)
 {
 	const char *str, *pos;
@@ -133,6 +153,7 @@ static const struct sheep_sequence string_sequence = {
 	.concat = string_concat,
 	.reverse = string_reverse,
 	.nth = string_nth,
+	.slice = string_slice,
 	.position = string_position,
 };