Hi, The docs for newArray# states: "Create a new mutable array of specified size (in bytes), in the specified state thread, with each element containing the specified initial value." Why is the size in bytes? Is Array# meant to be used both for boxed and unboxed values? For arrays of boxed values I'd expect the size to be the number of elements and the allocated size the number of elements multiplied by the size of a pointer. Are the docs correct? If so, how do I allocate an Array# of pointers? I'm trying to implement the following array type: data MurableArray s a = Array { unArray :: !(MutableArray# s a) } i.e. an array of boxed values. I can't figure out how to write new :: Int -> a -> ST s (MutableArray s a) where the first argument is the number of elements (of type a). Johan