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@wwwwwwwwww you have been hell-banned and I dont see anything particularly offensive in your immediate comment history. > is there any reason to add lazy evaluation to c++ [...] I think you are suffering from a misapprehension. Nothing is being added to C++ the language. This is just an implementation of lazy streams in C++14. Think of it as an optional 3rd party library. > lazy evaluation is one of those features wh…
honest question: is there any reason to add lazy evaluation to c++ other than to just add more features to the language? lazy evaluation is one of those features where i have absolutely no idea what benefit it actually provides
honest question: is there any reason to add lazy evaluation to c++ other than to just add more features to the language? lazy evaluation is one of those features where i have absolutely no idea what benefit it actually provides
honest question: is there any reason to add lazy evaluation to c++ other than to just add more features to the language? lazy evaluation is one of those features where i have absolutely no idea what benefit it actually provides
For example, let's look at a canonical quicksort in Haskell:
quicksort :: Ord a => [a] -> [a]
quicksort [] = []
quicksort (p:xs) = (quicksort lesser) ++ [p] ++ (quicksort greater)
where
lesser = filter (= p) xs
In Python, this would probably be done like this:
def min_list(lst):
current_minimum = lst[0]
for e in lst[1:]:
if e minimum xs = head (quicksort xs)
Now, if have the slightest care for efficiency, you would never, ever write a function like this in a strict language.
However, in Haskell, minimum [5,2,7,1,3] would be evaluated like this:
> minimum [5,2,7,1,3]
> head (quicksort [5,2,7,1,3])
> head (lesser ++ ...) [p = 5]
> head ((quicksort (filter ( > head ((quicksort (2:(filter ( head ((quicksort (filter ( > head ( [] ++ [1] ++ ...)
> head ([1] ++ ...)
> 1
I personally believe that the expressiveness gained through this procedure(we wrote quicksort and gained minimum for free!) offsets the loss in efficiency.
Earlier quoted context omitted.
But in a language with mutating side effects, and iterators, I'm not sure what this buys you over: for (auto& num = file.line_iterator(); num != file.end(); num++) { if (atoi(num) == 42) return true; return false; Note that 'line_iterator()' isn't something that (as far as I know) is defined in the C++ standard library, but there's nothing preventing it.
> But in a language with mutating side effects, and iterators, I'm not sure what this buys you... Side-effect free, functional style of programming.
Earlier quoted context omitted.
>lazy evaluation is one of those features where i have absolutely no idea what benefit it actually provides Good question. Let's say you have a program like this little python example: inputs = [raw_read() for i in range(1000)] # Read numbers from command line numbers = map(int, inputs) # Turn them into integers for num in numbers: # Check for 42 if num == 42: return true return false # It's not there If you use lazy…
But in a language with mutating side effects, and iterators, I'm not sure what this buys you over: for (auto& num = file.line_iterator(); num != file.end(); num++) { if (atoi(num) == 42) return true; return false; Note that 'line_iterator()' isn't something that (as far as I know) is defined in the C++ standard library, but there's nothing preventing it.
Lazy evaluation gets you all that, with no extra code, all the time.
Imagine writing that iterator stuff for every single applicable thing in the entire program. There are also other places where lazy evaluation is useful and you can't use iterators, like a function that will only use a portion of its arguments depending on some condition.
@wwwwwwwwww you have been hell-banned and I dont see anything particularly offensive in your immediate comment history. > is there any reason to add lazy evaluation to c++ [...] I think you are suffering from a misapprehension. Nothing is being added to C++ the language. This is just an implementation of lazy streams in C++14. Think of it as an optional 3rd party library. > lazy evaluation is one of those features wh…
How would this lazy-vector-mapping compare to the optimizations used in std::valarray? Or are those optimizations just the ones you mention here?