[Haskell-beginners] Brainfuck interpreter stack overflow

Hello, I just started using haskell and found it many uses for it (mainly for scripting purposes at the moment). Now, I have written a brainfuck parser and interpreter in haskell, but it produces a stack overflow if the program runs too long and I don't understand why. I thought I made the interpreter loop tail recursive, which I understood is the most common cause of a stack overflow. Can someone help my find my fault? I somehow miss something. I added the program as attachment. Thanks for your help. With kind regards, Edgar Klerks