[Haskell-cafe] Do real programs need IO? (was IO is a bad example
conal at conal.net
Sun Dec 9 15:29:55 EST 2007
I think your real point is that some things we still haven't figured out how
to express functionally. Right? I would certainly agree with that part.
Perhaps you exaggerating when you wrote "IO is important because you can't
write any real program without using it."
Cheers, - Conal
On Dec 9, 2007 12:14 PM, Lennart Augustsson <lennart at augustsson.net> wrote:
> I think TV etc. is fantastic stuff, but that mean that we cannot, say,
> invoke an external program in Haskell until someone has figured out a
> composable library for this?
> I sincerely hope someone will, but the only way we have right now is the
> ugly IO monad.
> -- Lennart
> On Dec 9, 2007 7:26 PM, Conal Elliott <conal at conal.net> wrote:
> > On Dec 9, 2007 10:07 AM, Daniel Fischer <daniel.is.fischer at web.de>
> > wrote:
> > > Interactive programmes without using IO? Cool :)
> > And how!
> > > I think you misunderstood Lennart.
> > Thanks for checking. In this case, I think I understood Lennart fine
> > and that he was saying what you're saying.
> > > Would you deny that any useful programme has to do at least some of
> > the following:
> > > -accept programme arguments at invocation
> > > -get input, be it from a keyboard, mouse, reading files, pipes...
> > > -output a result or state info, to the monitor, a file, a pipe...
> > ===
> > If by "programme", you mean the code I write, then I'm happy to deny
> > that my programme has to do these things. Examples below. If you include a
> > stateful RTS, then no I don't deny it.
> > > I think Lennart was referring to that, you HAVE to know a little IO to
> > write
> > > programmes, at least getArgs, getLine, putStr(Ln), readFile,
> > writeFile,
> > > appendFile. And therefore some use of the IO monad has to be taught
> > > relatively early.
> > Explicit imperative programming is just one way to deal with input &
> > output, not the only way. As proof, see FRP, Pan, or TV programs, which
> > contain uses of none of these functions. (Nor could they, as these
> > libraries are functional, having IO-free types and semantics.) Moreover,
> > use of imperative programming sacrifices some of the semantic simplicity &
> > composability that makes FP so appealing. That's why I'd like to see this
> > belief in its necessity dispelled.
> > That said, I don't think the existing functional (non-IO) approaches to
> > interaction are quite there yet with the flexibility of imperative
> > programming. It will take more work to get them there, and that work is
> > mostly likely to be pursued by people who doubt the necessity of IO for
> > writing "real programs". In that sense, Lennart's and your statements are
> > self-fulfilling prophechies, as are mine.
> > BTW, if you haven't seen it already, please check out
> > http://haskell.org/haskellwiki/TV . The TV (tangible values) approach
> > includes a simple algebra of interfaces (input/output) and keeps separable
> > from the core computation. The separability allows the interface parts to
> > be composed in parallel with the core part. For instance, when two
> > function-valued TVs are composed, the interfaces are peeled off, so that the
> > core functions can be composed directly. The output half of one interface
> > and the matching input half of the other are discarded. The remaining input
> > and output halves are recombined into a new interface, which is used as the
> > interface of the composed TV. The core interface algebra can be used for
> > text stream i/o, GUIs, and many other possible styles of information
> > passing.
> > I mention TV, because it's an example of combining the purity &
> > composability I love about FP with the usability a "real" app. For more
> > about this combination, please see my Google tech talk "Tangible Functional
> > Programming: a modern marriage of usability and composability" (
> > http://conal-elliott.blogspot.com/2007/11/tangible-functional-programming-modern.html).
> > That talk focus on end-user composability, but the essential points apply as
> > well to explicit programming. As I mentioned before, TV (a) is currently
> > less flexible than imperative/IO programming, and (b) has the composability,
> > guaranteed safety, and amenability to reasoning of pure functional
> > programming.
> > Cheers, - Conal
> > Am Sonntag, 9. Dezember 2007 18:31 schrieb Conal Elliott:
> > > > > IO is important because you can't write any real program without
> > > using
> > > > > it.
> > > >
> > > > Ouch! I get awfully discouraged when I read statements like this
> > > one. The
> > > > more people who believe it, the more true it becomes. If you want
> > > to do
> > > > functional programming, instead of imperative programming in a
> > > functional
> > > > language, you can. For instance, write real, interactive programs
> > > in FRP,
> > > > phooey, or TV. And if you do, you'll get semantic simplicity,
> > > powerful &
> > > > simpler reasoning, safety and composability.
> > > >
> > > > - Conal
> > >
> > > > On Dec 8, 2007 1:26 AM, Lennart Augustsson < lennart at augustsson.net>
> > wrote:
> > > > [...]
> > > > IO is important because you can't write any real program without
> > using it.
> > > > So why not teach enough of it to get people off the ground straight
> > away?
> > > > People who hang around long enough to do some more Haskell
> > programming
> > > > will run into the other monads sooner or later. But IO is an
> > unavoidable step to
> > > > writing Haskell programs.
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