diff --git a/contents/verlet_integration/code/nim/verlet.nim b/contents/verlet_integration/code/nim/verlet.nim
index fc0ae08f8..d88a2e586 100644
--- a/contents/verlet_integration/code/nim/verlet.nim
+++ b/contents/verlet_integration/code/nim/verlet.nim
@@ -1,4 +1,4 @@
-proc verlet(pos_in, acc, dt: float): float =
+func verlet(pos_in, acc, dt: float): float =
   var
     pos: float = pos_in
     prevPos: float = pos
@@ -11,9 +11,9 @@ proc verlet(pos_in, acc, dt: float): float =
     pos = pos * 2 - prevPos + acc * dt * dt
     prevPos = tempPos
 
-  return time
+  time
 
-proc stormerVerlet(pos_in, acc, dt: float): (float, float) =
+func stormerVerlet(pos_in, acc, dt: float): (float, float) =
   var
     pos: float = pos_in
     prevPos: float = pos
@@ -29,9 +29,9 @@ proc stormerVerlet(pos_in, acc, dt: float): (float, float) =
 
     vel += acc * dt
 
-  return (time, vel)
+  (time, vel)
 
-proc velocityVerlet(pos_in, acc, dt: float): (float, float) =
+func velocityVerlet(pos_in, acc, dt: float): (float, float) =
   var
     pos: float = pos_in
     time: float = 0.0
@@ -42,15 +42,16 @@ proc velocityVerlet(pos_in, acc, dt: float): (float, float) =
     pos += vel * dt + 0.5 * acc * dt * dt
     vel += acc * dt
 
-  return (time, vel)
+  (time, vel)
 
-let timeV = verlet(5.0, -10.0, 0.01)
-echo "Time for Verlet integration is: ", timeV
+when isMainModule:
+  let timeV = verlet(5.0, -10.0, 0.01)
+  echo "Time for Verlet integration is: ", timeV
 
-let (timeSV, velSV) = stormerVerlet(5.0, -10.0, 0.01)
-echo "Time for Stormer Verlet integration is: ", timeSV
-echo "Velocity for Stormer Verlet integration is: ", velSV
+  let (timeSV, velSV) = stormerVerlet(5.0, -10.0, 0.01)
+  echo "Time for Stormer Verlet integration is: ", timeSV
+  echo "Velocity for Stormer Verlet integration is: ", velSV
 
-let (timeVV, velVV) = velocityVerlet(5.0, -10.0, 0.01)
-echo "Time for velocity Verlet integration is: ", timeVV
-echo "Velocity for velocity Verlet integration is: ", velVV
+  let (timeVV, velVV) = velocityVerlet(5.0, -10.0, 0.01)
+  echo "Time for velocity Verlet integration is: ", timeVV
+  echo "Velocity for velocity Verlet integration is: ", velVV