In C you can't implement main loop with recursion like

void mainLoop() {

  doSomething();

  mainLoop();

}  

because without optimisations stack will overflow.

In haskell it's common to write

mainLoop = doSomething >> mainLoop, and it doesn't leak memory because of haskell's evaluation model.

Does memory leak or argument stack overflow happen in this case?

mainLoop = doSomething >> mainLoop >> exit ExitSuccess

What about this case?

mainLoopModeA = do

  doSomething

  when condition mainLoopModeB

  mainLoopModeA

mainLoopModeB = do

  doSomethingElse

  when anotherCondition mainLoopModeA