Hi, Shishir, As a recovering complexity addict (i.e. Java programmer ;-), I'd put it this way. There are many methods (on many types) that can either succeed and return a meaningful value, or be unable to fulfill the intent of the caller's request. Example include indexOf on String, get on Map, and read on a Reader. Every time such a partial function scenario occurs, the author must decide what to do if the intent can't be fulfilled. That freedom of choice has led to a proliferation of techniques. - indexOf returns -1, which is a valid int, but not a valid position within a string. - get returns null, which is the only value common to all reference types that means 'I have nothing'. Of course, that also prevents one from storing null in a Map and simply retrieving it. Worse, if that result is passed along elsewhere, one can eventually receive a NullPointerException occurring in a completely different part of the code. - And, *horrors!*, read responds in a totally different way, by forcing the caller to "jump" somewhere. Maybe provides a general, reusable solution to all such cases. - It allows one to "stretch" any type to include an extra "out of band" value. - The type declaration clearly (uniformly) notifies anyone else that the function may have to return "lack of result". - The type system prevents a caller from simply assuming that a result is present, and then accidentally propagating failure. - Because Maybe is an instance of Functor, one can use map to safely apply a function (or do nothing gracefully) without littering the calling code with if-statements. - etc. I don't think of Maybe as enabling a *computation* that is impossible otherwise, but I do regard it as providing a *consistency and simplicity* that is otherwise not present. Hope this helps, Joel On Thu, Mar 26, 2015 at 5:06 AM, Shishir Srivastava < shishir.srivastava@gmail.com> wrote:
Hi,
After reading and re-reading the haskell tutorials I don't happen to see a very convincing or appealing reason for having these data types.
Can anyone please explain where Maybe and Just provide the sort of functionality that cannot be achieved in other languages which don't have these kind.
Thanks, Shishir Srivastava
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