[jiaweihli]

This is slightly different from the original code. The reason for all the flatmapping is to avoid continuation if any of the subparsers fail, and notify the caller that something has failed because of {some exception}.

You can avoid excessive nesting/flatmapping with some syntax sugar, but it needs to be sufficiently different from normal declarative code.

[jsprogrammer]

I alluded to that in my last note. :)

If you properly define the functions (`c`, `f`, `g`, `t`), you can get the semantics of halted computation on failure. That is essentially what Haskell's `do` notation does.