1 files changed, 57 insertions, 0 deletions
diff --git a/usth/ICT2.1/labwork/2/construct.c b/usth/ICT2.1/labwork/2/construct.c
new file mode 100644
index 0000000..db32d8a
--- /dev/null
+++ b/usth/ICT2.1/labwork/2/construct.c
@@ -0,0 +1,57 @@
+/*
+ * Lisp construct implementation.
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#include <stdlib.h>
+
+#include "construct.h"
+
+construct *cons(void *first, construct *rest)
+{
+	construct *list = malloc(sizeof(construct));
+	list->car = first;
+	list->cdr = rest;
+	return list;
+}
+
+void *car(construct *list)
+{
+	return list->car;
+}
+
+construct *cdr(construct *list)
+{
+	return list->cdr;
+}
+
+size_t length(construct *list)
+{
+	if (list == NULL)
+		return 0;
+	return length(cdr(list)) + 1;
+}
+
+void *nth(construct *list, size_t n)
+{
+	if (list == NULL)
+		return NULL;
+	return n ? nth(cdr(list), n - 1) : car(list);
+}
+
+/*
+ * Try to insert x before item of index i and return the new construct.
+ * Return NULL on invalid index.
+ */
+construct *insert(void *x, construct *list, size_t i)
+{
+	if (!i)
+		return cons(x, list);
+	if (list == NULL)
+		return NULL;
+
+	void *first = car(list);
+	construct *rest = cdr(list);
+	free(list);
+	return cons(first, insert(x, rest, i - 1));
+}