[Haskell-cafe] Re:Explaining monads
jeff.polakow at db.com
Wed Aug 15 10:59:27 EDT 2007
> Hence the need to perform a "run" operation like runIdentity,
> evalState or runParser (for Parsec) to get something useful to
> happen. Except for lists we don't seem to do this. I suppose lists
> are so simple that the operators :, ++ and the  constructor do all
> we ever need with them. Finally there is no runIO because "main" is
> essentially that function in every real program? - Greg
For lists, head is probably the simplest "run" operation.
As Brian noted earlier unsafePerformIO is a way to "run" IO computations
within your code; but doing so breaks the abstraction of IO as being the
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