On Sun, Sep 16, 2012 at 8:18 PM, Tillmann Rendel < ren...@informatik.uni-marburg.de> 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 > <http://blog.languager.org> > Very nice! Except that perhaps I'd rewrite the last line as: ...makes Haskell a good language for playing with alternative paradigms of side-effecting computation though mine is not as pithy as yours! Rusi http://blog.languager.org
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