Exercise the garbage collector

memexercise.sml

fun genVec n = Vector.tabulate(n, fn i => i)

local val gen = Random.newgenseed 42.0 in 
fun random_length () = Random.range(500, 200*16192) gen
fun range rng = let val f = Random.range rng in fn () => f gen end
end

fun initial n = List.tabulate(n, fn _ => genVec(random_length()))

fun split_at i lst =
    let fun loop 0 ahead after   = (rev ahead, after)
	  | loop n ahead (x::xs) = loop (n-1) (x::ahead) xs
	  | loop _ _ _           = raise Fail "Cannot happen" 
    in  loop i [] lst end 

fun doit n m = 
    let val rand_elem = range (0, n-1)
	val zero = Vector.tabulate(100, fn _ => 0)
	fun loop 0 _ = ()
	  | loop j lst =
	    let val _ = lst@[zero] = lst
		val i = rand_elem()
		val (ahead, after) = split_at i lst
	    in  print ("looping "^Int.toString j^"\n")
	      ; loop (j-1) (ahead @ (genVec(random_length())) :: List.tl after) 
	    end
    in  loop m (initial n) end
	    
val main : unit = doit 100 50;