On Mon, Aug 9, 2010 at 4:33 AM, wren ng thornton <wren@freegeek.org> wrote:

aditya siram wrote:

Thanks all for you suggestions!
Upon further reflection I realized that my audience is more pragmatic than
theoretical. Instead of emphasizing how monads are constructed and the monad
laws I think I want to dive right into the most common and useful monads.

>From my vantage point they are (in no particular order) : Reader, Writer,

State, IO, ST, STM, Parsec (have I missed any?) and of course the
transformer versions. I am debating whether or not to add [] to the bunch.

Whether you add [] or not, you should definitely include Maybe. Maybe captures the most basic kind of fallible computation, so it shows up all over the place with pragmatic coding. Compare against null pointers, returning -1 to signal error when a positive number is the expected return, using 0 to express an infinite limit on some kind of resource, etc. Maybe does the same thing, except it does them cleanly and correctly because we express the possibility of failure in the type system instead of relying on "magic values" to express them. Magic values are even worse than magic numbers and other magic constants, IMO.

Once you've explained Maybe, you can mention (Either a) in passing; they should figure out the generalization immediately.

--
Live well,
~wren

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