[Haskell-cafe] Do real programs need IO? (was IO is a bad example for Monads)

Sun Dec 9 19:56:32 EST 2007

Maybe I'm exaggerating, but it's true for 96% of all programs.  (96% is with
a :-))
I did not express anything that was meant to be a perpetual truth, only best
practice at the moment.

For a living I write programs that are almost without interaction with the
outside world. Still, I need a to spend 1% of the code doing IO related
stuff and it's very important that I can do it.  The other 99% are just pure
computations.
But that I think that validates rather than invalidates my point.

  -- Lennart

On Dec 9, 2007 8:29 PM, Conal Elliott <conal at conal.net> wrote:

> 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:
>
> > Conal,
> >
> > 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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> > >
> > >
> >
>
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