Figured out why future crashed, added in simple threading library. Future isn't fixed yet, but could be with a similar approach

tests/test_thread.expected_results

@@ -0,0 +1,5 @@
+hello from main first
+hello from thread first 1347
+hello from main middle
+hello from thread second 1347
+hello from main after join

tests/test_thread.krak

@@ -0,0 +1,20 @@
+import io:*
+import os:*
+import thread:*
+
+fun main(): int {
+    var a = 1337
+    println("hello from main first");
+    var t = run(fun(l: int) {
+        print("hello from thread first ")
+        println(a+l)
+        system("sleep 2")
+        print("hello from thread second ")
+        println(a+l)
+    }, 10)
+    system("sleep 1")
+    println("hello from main middle");
+    join(t)
+    println("hello from main after join");
+    return 0
+}