So, yes, it is useful, but should it be included in a standard Monad module? After all, this module contains mostly trivial functions ;)
BTW. You can write this function using foldM:
compM l a = foldM (#) a l
where # is an often used reverse application operator: x # f = f x
Right. Now that I look at it, someone probably tried to give me this advice before but I failed to understand... (sorry monotonom!). It's all clear now. One more question. Isn't the foldM description a bit misleading? From the Report and also in GHC documentation: "The foldM function is analogous to foldl, except that its result is encapsulated in a monad.(...) foldM f a1 [x1, x2, ..., xm ] == do a2 <- f a1 x1 a3 <- f a2 x2 ... f am xm" After reading this I expected "left associativity", just like in my first definition. That'd mean a fail wouldn't stop a computation immediately but instead be passed from function to function. By checking its definition in the report I can see this is not the case though. Cheers, J.A.