[Haskell-cafe] IO semantics and evaluation - summary

Daryoush Mehrtash dmehrtash at gmail.com
Fri Feb 13 14:31:06 EST 2009

I have been trying to figure out the distinction between value, function and
computation.     You raised a few points that I am not sure about.

In " "Computation" considered harmful. "Value" not so hot either." you said:

I still don't like it; a lambda expression is not a computation, it's a
formal *representation* of a mathematical object (a *value*).

Isn't the lambda expression a representation of  something (potentially with
recursion) that yields "a value" and not the value itself?   Even integer
which we think of as values are represented in the same way:

In " Fixing Haskell IO" you say:

This "works" well enough; GHC manages to perform IO. But it doesn't fly
> mathematically. Mathematical objects *never* act, sing, dance, or *do*anything. They just are. A value that acts is an oxymoron.

I guess I am not sure what a "mathematical object" is.   Do you consider
Newton method a mathematical object?   What would be the "value" :

Since I have been thinking about Haskell, Monads, etc. I am starting to
think about the  saying "Life is a journey, not a destination" to imply life
is a computation not a value.


2009/2/13 Gregg Reynolds <dev at mobileink.com>

> Many thanks to everybody who tried to set me straight on the thread about
> IO monad and evaluation semantics.  I've begun summarizing the info, and I
> believe I've come up with a much better way of explaining IO; just flip the
> semantic perspective, and think in terms of interpretations instead of
> actions.  Voila!  Oxymoron (values that perform actions) eliminated.   See
> the "Computation considered harmful" and "Fixing Haskell IO" articles at
> http://syntax.wikidot.com/blog
> Naturally I would be grateful for any corrections/comments.
> Thanks,
> gregg
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