[Haskell] Newbie: what are the advantages of Haskell?

Taillefer, Troy (EXP) troy.taillefer at lmco.com
Fri Apr 27 09:47:50 EDT 2007

Java sense (i.e. "cut out any feature that can't be understood in five
minutes by a chimp")
Got to love comments like this they are constructive, objective, mature
and accurate. 
Glad we have your expert opinion to give us the gospel. 
Can I get an amen? How about a Hallelujah ?
Troy Taillefer Java chimpanzee


From: haskell-bounces at haskell.org [mailto:haskell-bounces at haskell.org]
On Behalf Of Sebastian Sylvan
Sent: Thursday, April 26, 2007 1:27 PM
To: phiroc at free.fr
Cc: haskell at haskell.org
Subject: Re: [Haskell] Newbie: what are the advantages of Haskell?

(note to Haskellers: Yeah, I'm handwaving things here, no need to point
out counter-examples to my generalisations!)

On 4/26/07, phiroc at free.fr <phiroc at free.fr> wrote:
We'll do this one first:

What are the mysterious "side effects" which are avoided by using
Haskell, which 
everyone talks about? Null pointers?

Side effects are usually things like mutable state. In Haskell variables
don't vary. "x=x+1" isn't valid in Haskell. This means, among other
things, that functions always do the same thing given the same input
(they can't depend on some mutable state changing value), which is great
since you'll never get those "oh I forgot that I must first call foo
before I call bar, or I'll get an error". This really is a HUGE win,
since programming with state is unreasonably error-prone. I'm afraid
it's next to impossible to convince anyone that this is true, unless
they're willing to give it a serious try, though :-) 

Null pointers are possible when you're dealing with C functions mostly.
You don't use pointers in Haskell normally, only when you're interfacing
with external C libraries etc.

	what are the advantages of haskell over semi-functional
programming languages
	such as Perl, Common Lisp, etc.?

For me? Purity. I mean you can get plenty of the benefits of FP in any
old language (witness C# 3.0), but the one thing you can never get by
just adding support for a "functional style" in another language is
purity. Once purity is gone, it's gone! It can't be retrofitted on an
existing language.

Purity is great because it makes it much easier to write programs
without making silly mistakes. When writing programs in languages with
lots of side effects you have to sort of keep a "mental log" in your
head for all possible execution paths ("in this branch x is equal to y
plus w, and this pointer here is null in the other branch x is null
and..."). For me I can quite literally *feel* "brain resources" being
freed up when using Haskell, which I can use to get stuff done quicker
(or probably more accurate: I can feel how much brainpower I waste on
book keeping and keeping track of this "mental log" when using languages
like C++). 

Also purity is very interesting when you want to paralellize programs (a
pure function can be executed on any thread, at any time, and its
guaranteed to never interfer with the computation of other functions --
in impure languages this doesn't hold at all!). This is probably the
killer app for functional programming IMO. FP is cool for a number of
reasons, but I think "isn't almost unusable in a multithreaded setting"
is what sets it apart the most from imperative languages. 

Haskell also has STM which is great for that low level shared state
concurrency that you sometimes need (no locks, monitors, or any of that
non-composable, insanity-inducing, messiness!)

	Aren't Haskell's advantages outweighed by its complexity
(Monads, etc.) and

I can sometimes feel that Haskell looses out on not being user friendly
in the Java sense (i.e. "cut out any feature that can't be understood in
five minutes by a chimp"). Some things do take some effort to learn, but
there is a huge payoff for it (it's really powerful!). But yeah, there
might be plenty of folks who will never bother learning about them, and
they won't understand your code. 

Sebastian Sylvan
UIN: 44640862 
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