def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n-1)
def factorial(n):
return 1 if n == 0 else n * factorial(n-1)
def factorial(n):
return eval('*'.join(map(str, range(1, n+1))))
def factorial(n):
return reduce(lambda x, y: x * y, range(1, n+1))
def factorial(n):
def facts():
n, r = 1, 1
while True:
r, n = n*r, n+1
yield r
return next(islice(facts(), n-1, None))
So yes, you can write things lots of ways in Haskell. But, if you had production code in Haskell, you wouldn't try to be clever, in the same way that you wouldn't (or shouldn't) try to be clever in production code in Python. You'd write simple, straightforward code, just like
fact n = prod [1..n]It doesn't mean that the language design is going to somehow ensure there's only one way (even only one idiomatic way) for users to implement any particular algorithm. It doesn't mean everyone has to use the same web framework. It's really not prescriptive, except for Python itself.
You can overcomplicate things in any language. Haskell gives you better tools for dealing with complexity - which some people use as a reason to push the complexity to the limit. But if you stick to abstractions that are actually providing value (e.g. by letting you reduce code duplication) you'll find it's a very good language.
Though, if you need hard real time, even C can be tricky.
Haskell can be written for soft real time things, but it's also tricky. Rust might be a better bet?
A lazy language is probably not the answer to this particular problem.
All tests are thus 100% reliable and parallelizable.
This capability of isolating and controlling side effects makes Haskell very uniquely well-suited to applications that need to withstand a lot of maintenance by a lot of people for a very long time.
The general high-level approach is that your business logic functions run in some monad, constrained by the set of capabilities it requires. Each capability is represented as a typeclass.
Your type signatures say that your business actions work in every monad that supports those capabilities, so the type checker rejects any code that tries to use "unblessed" side effects.
The vast majority of examples on the page are curiosities which appeal to some people and arise from all the academic attention both given to Haskell and which Haskell permits. You can be a competent and highly-effective Haskell programmer without understanding the majority of these.
"Maybe" still blew my mind away first time I saw it...MAYBE?? MAYBE?? :D. Sure it would all be beautiful if I spent time learning it.
In practice, there are some of the examples that are more important than the others:
- The "accumulating" version might use less stack-space than the naive recursion so its a very important technique to learn.
- The foldl version is a more structured version of the accumulating version, kind of like how a for loop if is more structured than a goto.
- The memoizing (aka caching) version is useful if your funcion is very expensive to compute.
- And the "tenured professor" obviously makes the best use of the existing syntactic suger :)
The rest of the entries are a bit more overkill for a factorial program.
In light of that, I would definitely recommend Haskell over other languages for any use cases where you expect you're going to be wrong, repeatedly, about how best to structure your program. Especially in domains that aren't known very well or when the demands on the program are likely to be highly dynamic.
Though really, at this point I would tend toward using Haskell when there is not much reason to pick something else.
Functional programming is arriving right now, but not as Haskell.
As an aside, I think of Haskell as a sensei/guru saying, "Young grasshopper, if you want access to the glory that is my wisdom you will have to wash my dishes and scrape off my calluses for the next three years" to which my personal reply is "Hell no". It¨s unfriendly and it doesn't respect my time. Is there wisdom in Haskell? Probably, but I don't have the patience to deal with the bullshit.
I don't think Haskell itself will ever be the language of choice, it'll probably fall into (remain in?) a smalltalk like life.
That said, functional idioms seem to be creeping into lots of mainstream languages, so it's not like never. Rust seems pretty heavily influenced by ml, and somewhat by haskell.
Mainstream languages have lambdas, more immutability and stronger types? That's great (non-sarcastically!). Haskell now has GADTs, rank-n types, polymorphic kinds, type families (poor name for type-level functions), and more.
These things make Haskell still quite compelling over other more mainstream languages, if you're willing to learn.
In some sense, yes. On the other hand, there are diminishing returns. As an example, the increase in software quality from a Java-like language adopting any of algebraic data types, parametric polymorphism or first class higher order functions is probably much bigger than Haskell moving to full on dependent types.
In any case, your point stands and complements mine.
(Apropos ADTs, did Scala always have them? From what I can tell their syntax is pretty awkward, though.
Google's Protobuf, which in some sense denotes a type system, even if not a programming language, did get something like ADTs: https://developers.google.com/protocol-buffers/docs/proto3#o...
I am pretty lenient, and would go for anything that resembles a compiler-enforced tagged union. (Think C-style union.))
http://www.boost.org/doc/libs/1_60_0/doc/html/variant.html ??? (and I think it's supposed to be coming in c++17)
either :: (a -> c) -> (b -> c) -> Either a b -> cIn the case of Haskell, it is taken as a badge of virtue, and it is a matter of faith that the problem is just that all other programming languages have mis-educated everyone who doesn't "get religion" about Haskell.
If Haskell's interface is hard to understand, that is a problem with Haskell.
Evidence that Haskell was deliberately made difficult to understand? And supposing this were true, why hasn't anyone made the interface more intelligible?
> If Haskell's interface is hard to understand, that is a problem with Haskell.
That's a bit like saying that if the mathematics used in the General Theory of Relativity is hard to understand, it is a problem with the General Theory of Relativity.
Well, but that's true; if there were easier-to-understand mathematics that had equal utility, it would be superior. The math being hard to understand is a problem, but (as far as anyone can tell), its a necessary cost with General Relativity.
So, for Haskell -- granting, for the sake of argument, that it is particularly hard to understand (which I'm not sure is really the case) -- the question is the complexity a necessary price for some benefit that is worth the cost?
And before you think I'm just hating on Haskell, the same is essentially true of Lisp as well.
I'm not sure how this is different than introducing a block in C.
What would be the C equivalent of:
(let ((last-response))
(defun get-response ()
(print last-response)
(setf last-response (read))))
(print (get-response))
(print (get-response))
Since the variable in question is only used in one function, you could declare the variable static to that function. It takes some care to make this reentrant, but that's possibly the case in lisp as well.
To share between multiple top-level functions, you can only limit scope to the individual file.
The bigger thing C can't do that lisp can here is defining new functions in arbitrary places. In C variants where you can define local functions, you can indeed capture variables in local scope. And within a function, you can limit scope by creating a new block:
int test() {
int foo = 7;
{
int foo = 9;
}
return foo; // returns 7
}
(let ((x))
(defun func1 ())
(defun func2 ()))
Yes, I mentioned that static variables in a function would not extend to multiple functions.
You can share a variable between a restricted set of top level functions by grouping those functions in a single object file that does not expose the variable in question.
I think my only objection is that your phrasing implied what's different is the explicitness of the scoping, when it's actually the flexibility of how functions can be defined (unsurprising, from a lisp).