Martin Hofmann wrote:
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?
A program that exits with <<loop>> is basically a program that runs forever. Examples of programs that run forever are let x = x + 1 in x let f x = f x in f 1 In special cases, the run-time system is able to detect that the program would run forever, and exits with <<loop>> if that happens.
Sorry, a lot of questions at once, but I am kind of helpless because I can't find any reason of my <<loop>>, so any comments, experience, and tips are highly appreciated.
Sometimes, a simple cause is accidentally using the same variable name, i.e. writing let (c,s) = foobar s in ... while you meant let (c,s') = foobar s in ... At other times, non-termination is caused by not using enough irrefutable patterns. But this usually only happens when writing algorithms that heavily exploit recursion and laziness, which probably doesn't apply to your case. You may want to try the new GHCi debugger, maybe it helps finding the loop. Regards, H. Apfelmus