laziness | Rails plugin to create tests | Testing library

Method 1

The usual, very fast, and works great.

I want to be able to do something like this:

I understand that many of the names in Haskell are inspired by category theory terminology, and I'm trying to understand exactly where the analogy begins and ends.

I already know that Hask is not (necessarily) a category due to some technical details about strictness/laziness and seq, but let's put that aside for now. For clarity,

• The objects of Hask are concrete types, that is, types of kind *. This includes function types like Int -> [Char], but not anything that requires a type parameter like Maybe :: * -> *. However, the concrete type Maybe Int :: * belongs to Hask. Type constructors / polymorphic functions are more like natural transformations (or other more general maps from Hask to itself), rather than morphisms.
• The morphisms of Hask are Haskell functions. For two concrete types A and B, the hom-set Hom(A,B) is the set of functions with signature A -> B.
• Function composition is given by f . g. If we are worried about strictness, we might redefine composition to be strict or be careful about defining equivalence classes of functions.

I don't think the technicalities above have anything to do with my confusion below. I think I understand it means to say that every instance of Functor is an endofunctor in the category Hask. Namely, if we have

Getting started with lazy loading. I have an order with order details.

From Real World Haskell I read

It operates as follows: when a seq expression is evaluated, it forces its first argument to be evaluated, then returns its second argument. It doesn't actually do anything with the first argument: seq exists solely as a way to force that value to be evaluated.

where I've emphasised the then because to me it implies an order in which the two things happen.

From Hackage I read

The value of seq a b is bottom if a is bottom, and otherwise equal to b. In other words, it evaluates the first argument a to weak head normal form (WHNF). seq is usually introduced to improve performance by avoiding unneeded laziness.

A note on evaluation order: the expression seq a b does not guarantee that a will be evaluated before b. The only guarantee given by seq is that the both a and b will be evaluated before seq returns a value. In particular, this means that b may be evaluated before a. […]

Furthermore, if I click on the # Source link from there, the page doesn't exist, so I can't see the code of seq.

That seems in line with a comment under this answer:

[…] seq cannot be defined in normal Haskell

On the other hand (or on the same hand, really), another comment reads:

The 'real' seq is defined in GHC.Prim as seq :: a -> b -> b; seq = let x = x in x. This is only a dummy definition. Basically seq is specially syntax handled particularly by the compiler.

Can anybody shed some light on this topic? Especially in terms of:

• What source is right?
• Is seq's implementation really not writable in Haskell?
  • If so, what does it even mean? That it is a primitive? What does this tell me about what seq actually does?
• In seq a b is a guaranteed to be evaluated before b at least in the case that b makes use of a, e.g. seq a (a + x)?

Context Hi all. I'm having problems and I've looked everywhere and I'm just not getting it. I'm following a youtube tutorial on RecycleView (Coding in flow) however, I'm coming from a tutorial on setting up a MainActivity with fragments so I'm trying to do this inside of a fragment. In the comments, people have had similar problems and he replied by saying that it's basically the same except that inside the fragment you should use getView() however that isn't working.

What I've done so far to remedy the problem I've been looking at SO threads (even ones that are from the same video) and I'm just not getting it, none of their solutions is working for me or the responses they got (if any) were very vague and non-helpful. I've also searched all 300+ comments from that youtube video and looked up other tutorials to see if there's a solution. Not relevant to the problem I'm having but just to get the point across that I've not just types this out of laziness. I've spent the whole day on this problem and I have nothing to show for it

What I need the code to do I need the code to function as per the tutorial found here. I don't believe that the onCreateView is the best place for my code as surely none of the views will be created until that has been run so findViewById wouldn't be possible but what can I do now then? where can I put that code so it will run.

My code

PhotosFragment

I'm looking to try to run a moderately expensive function on a large list of inputs, using part of the output of that function as one of its inputs. The code runs as expected, unfortunately it consumes a large amount of memory in the process (just under 22GiB on the heap, just over 1GiB maximum residency). Here is a simplified example of what I mean:

I am trying to implement Huffman compression in Haskell for learning purposes. So far I can successfully create the correct tree for a given String and I can get the correct path to a character from a specific tree. The signature of that function is like this:

I don't understand how laziness / eagerness works in Raku. More precisely how to force eagerness.

I get that Infinite List are lazy. What I don't understand is that some List that have an end are lazy, and why the eager method doesn't work in my case.

I have this example