GHC heap profiling with -hy - What is * (star)?

Question

When I profile my program's heap usage with -hy flag like

./prog +RTS -hy

I often see the constructor * in the results, along with other constructors such as [] and Word8.

What is the type * in this context? Is it related to kinds?

Answer 1

Quoted from Real World Haskell:

There's also some heap allocated data of unknown type (represented as data of type "*").

And in the GHC User's Guide:

For closures which have function type or unknown/polymorphic type, the string will represent an approximation to the actual type.

So, it means basically that the profiling doesn't have enough information to tell what type it is.