I'm afraid this kind of 5-minute talk makes sense only if you already know a lot about monads or are a computer scientist; not if you're a programmer who wants to learn a new language. For instance, this statement starts making sense only if you've seen a lot of examples of monads (maybe even read Moggi and Wadler) and want to understand the big picture.
"... when Haskell programmers want to perform a side effect, they explicitly construct a description of the side effecting computation as a value." And even then, what does it mean to "construct a description of the side effecting computation as a value" for the Maybe monad? An IO action or a State Monad action indeed are values that describe computations, but what computation does (Just 1) describe? It's the simple monads that are tricky to explain (I've seen a discussion to that effect in this forum and I wholeheartedly agree). --Bartosz On Sunday, September 16, 2012 7:49:51 AM UTC-7, Tillmann Rendel wrote: > > Hi, > > Kristopher Micinski wrote: > > Everyone in the Haskell cafe probably has a secret dream to give the > > best "five minute monad talk." > > (1) Most programming languages support side effects. There are different > kinds of side effects such as accessing mutable variables, reading > files, running in parallel, raising exceptions, nondeterministically > returning more than one answer, and many more. Most languages have some > of these effects built into their semantics, and do not support the > others at all. > > (2) Haskell is pure, so it doesn't support any side effects. Instead, > when Haskell programmers want to perform a side effect, they explicitly > construct a description of the side effecting computation as a value. > For every group of related side effects, there is a Haskell type that > describes computations that can have that group of side effects. > > (3) Some of these types are built in, such as IO for accessing the world > outside the processor and ST for accessing local mutable variables. > Other such types are defined in Haskell libraries, such as for > computations that can fail and for computations that can return multiple > answers. Application programmers often define their own types for the > side effects they need to describe, tailoring the language to their needs. > > (4) All computation types have a common interface for operations that > are independent of the exact side effects performed. Some functions work > with arbitrary computations, just using this interface. For example, we > can compose a computation with itself in order to run it twice. Such > generic operations are highly reusable. > > (5) The common interface for constructing computations is called > "Monad". It is inspired by the mathematical theory that some computer > scientists use when they describe what exactly the semantics of a > programming language with side effects is. So most other languages > support some monad natively without the programmer ever noticing, > whereas Haskell programmers can choose (and even implement) exactly the > monads they want. This makes Haskell a very good language for side > effecting computation. > > Tillmann > > _______________________________________________ > Haskell-Cafe mailing list > haskel...@haskell.org <javascript:> > http://www.haskell.org/mailman/listinfo/haskell-cafe >
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
