Hacking Haskell
rethrick.com
rethrick.com
Now I'm going to get a lot of flack here for saying this but I simply just don't feel that most of the stuff we make today is of particularly high craftsmanship. We need one of two things to happen.
The first is that the demand for thoroughly well-crafted software has to increase. But that much is out of our hands as it is conditional on the public at large. This will happen eventually. New tech starts life as a toy. At some point, people will want those toys to be reliable.
Going the other way, we could make it more rewarding for people to build scalable, maintainable systems in Haskell. But we are already well on the way to doing this. For example, Snap was much easier to use than Happstack (IMHO), and Happstack itself has already much improved over the years. The libraries for Couch and Mongo are as good as any other. Tools aside then, Haskell's main impediment is that can be a bit intimidating. But a friendly and openminded developer community can go a long way. We just have to keep this in mind, and keep fostering projects.
It's a somewhat outdated view of the community, which is now quite large, with many members gainfully employed building systems in Haskell commercially, and in non-trivial applications.
In particular, the question of efficiency in the context of lazy evaluation appears to be very tricky, and thus far it has been only little explored. For example, the first way to do large-scale I/O in Haskell that doesn't eat up resources (namedly, "iteratees") is maybe 3 years old, and I don't think an awfully lot of people really grasp it. No, it seems to me that we're just beginning to figure this stuff out.
Earlier comment:
Talk about just out-of-reach, how about the words on the page? Viewing this under FF3.6 on Snow Leopard, and the words go just off the right-hand side of the window, no matter what size I make it.
EDIT: Tried Safari. It's a fixed-width column there. And Readable works fine under FF.
Iteratees weren't introduced to solve the problem of "eating up resources" per se. They're a new abstraction for doing high performance IO -- in any language. You've always had several choices for IO in Haskell: lazy IO (like pipes in shell programming), or strict IO (like say, Python or C IO).
Iteratees blend these somewhat, giving a third way.
So you could say that IO isn't well explained by computer science yet -- as new approaches are still being discovered. That doesn't really say anything about Haskell, other than it was the first developer community to really take iteratee-style IO seriously.
In any case, my point about efficiency in the context of lazy evaluation not being well understood, still stands.
Many other programming techniques face similar barriers: e.g. memoization, concurrency or logic programming result in similar brain twisting -- yet can be suprisingly useful.
So I argue that programmers shouldn't be scared of technology -- embracing and learning new techniques can only improve your practice.
I don't think I could ever be sold on using a language where IO is an unsolved problem. Computer Science has defined it quite well for me in Python
Iteratees let you compose chains of highly-efficient producers, transformers and consumers.
As a relatively trivial example, how would you write something in Python that performs this:
for word in open("really_big_file", "rb").read().split(","):
socket.send(word[::-1])
def read_chunked(f, delim=',', size=1024):
buf = []
while True:
data = f.read(size)
if not data:
if buf:
yield ''.join(buf)
break
if delim in data:
spl = data.split(',')
buf.append(spl[0])
yield ''.join(buf)
for s in spl[1:-1]:
yield s
rest = spl[-1]
buf = [rest] if rest else []
else:
buf.append(data)
for word in read_chunked(open("really_big_file", "rb")):
#socket.send(word[::-1])
print word[::-1]
main = run_ $
enumFile someFile
$$ splitWhen isComma
$$ map reverse
$$ iterHandle stdout
where
isComma = (== ',') . chr . fromIntegral
* Generalized for any error type and support various modes of error handling/propagation (they can go up to the producer, or down towards the deeper consumer as error inputs).
* Are generalized to many types of "buffers"
* Have a high-performance counterparts of standard "list functions"
* Are a standard base for many libraries to extend (http, xml, etc), and are faster, more powerful and more useful than standard strict IO libraries (Haskell's base libs, and Python's stdlib).
So both Python and Haskell have standard "strict IO" libraries. Iteratees are really a new idea -- that Python does not do well yet. So I don't think Haskell's progression of the state of the art in IO handling is really evidence that "IO is unsolved in Haskell".
Can anyone elaborate?