--- a/core_testing1/collatz.scala	Wed Nov 01 15:01:32 2023 +0000
+++ b/core_testing1/collatz.scala	Thu Nov 02 11:32:10 2023 +0000
@@ -1,33 +1,27 @@
-import scala.annotation.tailrec
 // Core Part 1 about the 3n+1 conjecture
 //============================================
 
 object C1 {
 
-@tailrec
-private def collatz(n: Long, steps: Long = 0): Long = {
-  if (n == 1) steps
-  else if (n % 2 == 0) collatz(n / 2, steps + 1)
-  else collatz(n * 3 + 1, steps + 1)
-}
-
-def collatz_max(upper: Long): (Long, Long) = {
-  (1L to upper).map(n => (collatz(n), n)).maxBy(_._1)
-}
+def collatz(n: Long): Long =
+  if (n == 1) 0 else
+    if (n % 2 == 0) 1 + collatz(n / 2) else 
+      1 + collatz(3 * n + 1)
 
 
-private def is_pow_of_two(n: Long) : Boolean = {
-  (n & (n - 1)) == 0
+def collatz_max(bnd: Long): (Long, Long) = {
+  val all = for (i <- (1L to bnd)) yield (collatz(i), i)
+  all.maxBy(_._1)
 }
 
-private def is_hard(n: Long) : Boolean = {
-  is_pow_of_two(3 * n + 1)
-}
+def is_pow(n: Long) : Boolean = (n & (n - 1)) == 0
+
+def is_hard(n: Long) : Boolean = is_pow(3 * n + 1)
 
-
-private def last_odd(n: Long): Long = {
-  (1L to n).filter(is_hard).max
-}
+def last_odd(n: Long) : Long = 
+  if (is_hard(n)) n else
+    if (n % 2 == 0) last_odd(n / 2) else 
+      last_odd(3 * n + 1)
 
 }
 

--- a/core_testing1/collatz_test.sh	Wed Nov 01 15:01:32 2023 +0000
+++ b/core_testing1/collatz_test.sh	Thu Nov 02 11:32:10 2023 +0000
@@ -15,20 +15,21 @@
 # compilation tests
 
 function scala_compile {
-  (ulimit -t 30; JAVA_OPTS="-Xmx1g" scala -Xprint:parser "$1" 2> c$out 1> c$out)
+  (ulimit -t 30; JAVA_OPTS="-Xmx1g" scala-cli compile "$1" ) #2> c$out 1> c$out)
 }
 
 # functional tests
 
 function scala_assert {
-  (ulimit -t 30; JAVA_OPTS="-Xmx1g" scala -nc -i "$1" -- "$2" -e "" 2> /dev/null 1> /dev/null)
+  (ulimit -t 30; JAVA_OPTS="-Xmx1g" scala-cli -i "$1" "$2" -e "urbanmain()" ) #2> /dev/null 1> /dev/null)
 }
 
 # purity test
+function scala_vars {
+   (sed 's/immutable/ok/g' c$out > cb$out;
+    egrep '\bvar\b|\breturn\b|\.par\.|\.par |ListBuffer|AtomicInteger|mutable|util.control|new Array' cb$out 2> /dev/null 1> /dev/null)
+}
 
-function scala_vars {
-   (egrep '\bvar\b|\breturn\b|\.par\.|\.par |ListBuffer|AtomicInteger|mutable|util.control|new Array' c$out 2> /dev/null 1> /dev/null)
-}
 
 
 ### compilation test

--- a/core_testing1/collatz_test1.scala	Wed Nov 01 15:01:32 2023 +0000
+++ b/core_testing1/collatz_test1.scala	Thu Nov 02 11:32:10 2023 +0000
@@ -1,8 +1,10 @@
 
-import C1._
+def urbanmain() = {
+  import C1._
 
-assert(collatz(1) == 0) 
-assert(collatz(6) == 8)
-assert(collatz(9) == 19)
+  assert(collatz(1) == 0) 
+  assert(collatz(6) == 8)
+  assert(collatz(9) == 19)
 
+}
 

--- a/core_testing1/collatz_test2.scala	Wed Nov 01 15:01:32 2023 +0000
+++ b/core_testing1/collatz_test2.scala	Thu Nov 02 11:32:10 2023 +0000
@@ -1,8 +1,12 @@
-import C1._
+
+def urbanmain() = {
+
+  import C1._
 
-assert(collatz_max(10) == (19, 9))
-assert(collatz_max(100) == (118, 97))
-assert(collatz_max(1000) == (178, 871))
-assert(collatz_max(10000) == (261, 6171))
-assert(collatz_max(100000) == (350, 77031))
-assert(collatz_max(1000000) == (524, 837799))
+  assert(collatz_max(10) == (19, 9))
+  assert(collatz_max(100) == (118, 97))
+  assert(collatz_max(1000) == (178, 871))
+  assert(collatz_max(10000) == (261, 6171))
+  assert(collatz_max(100000) == (350, 77031))
+  assert(collatz_max(1000000) == (524, 837799))
+}

--- a/core_testing1/collatz_test3.scala	Wed Nov 01 15:01:32 2023 +0000
+++ b/core_testing1/collatz_test3.scala	Thu Nov 02 11:32:10 2023 +0000
@@ -1,4 +1,8 @@
 
-assert(C1.last_odd(113) == 85)
-assert(C1.last_odd(84) == 21)
-assert(C1.last_odd(605) == 341)
+def urbanmain() = {
+
+  assert(C1.last_odd(113) == 85)
+  assert(C1.last_odd(84) == 21)
+  assert(C1.last_odd(605) == 341)
+
+}