On Dec 10, 2007 1:44 PM, Dan Piponi <[EMAIL PROTECTED]> wrote: > When someone comes to me and says "I have this Python script that > scans through these directories and finds the files that meet these > criteria and generates a report based on this template, could I do it > better in Haskell?" it'd be good to have a better answer than "to do > this you could use the IO monad, but to do things properly you need to > understand monads so here, learn about the List monad and the Maybe > monad first, understand how this interface abstracts from both, come > back when you've finished that, and then I'll tell you how to read and > write files".
I thought your blog post about the IO monad for people who don't care about monads (yet) was a pretty good start. As it happens, the IO monad was one of the things that attracted me to Haskell. When I was learning SML in college, I wondered how one could do I/O in a functional style. SML provides I/O via functions with side-effects, which struck me as crude and contrary to the functional style. Years later, I encountered Haskell and learned that it handled I/O tasks using something called the "IO monad". I had no idea what a monad was, but I understood the implications: Haskell could be referentially transparent *and* do I/O. This was what inspired me to learn the language. As I learned more Haskell, I discovered the other monads and the Monad class and the full generality of the "do" notation. Eventually, a light came on and monads suddenly made sense. I don't know if it's best to learn the IO monad before or after other monads. I suspect no choice is right for everyone. An experienced programmer who is new to Haskell is going to have different questions than a beginning programmer with no preconceived notions. -- Dave Menendez <[EMAIL PROTECTED]> <http://www.eyrie.org/~zednenem/>
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