I am picking up a discussion with the same topic from haskell-users on 8th November. Thunks with reference on themselves was mentioned as main reason for <<loop>>.
A safe recursive definition would be let x = Foo (x+1) However, if you leave out the constructor, let x = x + 1 you get a <<loop>> (or a deadlock).
Are there any other reasons? I am trying to debug monadic code which stores state information in a record maintaining several Data.Maps, but in vein so far. A state is modified/changed in several steps by a compound function i.e. changeA $ changeB $ changeC state Is code using mtl, records or Maps more prone to <<loop>> or does this not matter at all. How can I identify self-referencing thunks more easily? Is there any rule of thumb to prevent <<loop>>? Are there any less obvious newbie mistakes causing <<loop> then the one above? Any comments, experience, and tips are highly appreciated. Thanks, Martin