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The indexing operation doesn't have an identity element. The domain and range of indexing is not necessarily the same -- the domain is arrays and objects, but the range is any type of object, since array elements and object properties can hold any type. If you have an array of integers, the domain is Array, while the range is Integer, so it's not possible for there to be an identity. a[x] will always be an integer, which can never be equal to the array itself.

And even if you have an array of arrays, there's no reason to expect any of the elements to be a reference to the array itself. It's possible to create self-referential arrays like this, but most are not. And even if it is, the self-reference could be in any index, so there's no unique identity value.

The most basic form of the kind language contains only * (or Type in more modern Haskell; I suspect we'll eventually move away from *) and ->.

But there are more things you can build with that language than you can express by just "counting the number of *s". It's not just the number of * or -> that matter, but how they are nested. For example * -> * -> * is the kind of things that take two type arguments to produce a type, but (* -> *) -> * is the kind of things that take a single argumemt to produce a type where that argument itself must be a thing that takes a type argument to produce a type. data ThreeStars a b = Cons a b makes a type constructor with kind * -> * -> *, while data AlsoThreeStars f = AlsoCons (f Integer) makes a type constructor with kind (* -> *) -> *.

There are several language extensions that add more features to the kind language.

PolyKinds adds kind variables that work exactly the same way type variables work. Now we can have kinds like forall k. (* -> k) -> k.

ConstraintKinds makes constraints (the stuff to the left of the => in type signatures, like Eq a) become ordinary type-level entities in a new kind: Constraint. Rather than the stuff left of the => being special purpose syntax fairly disconnected from the rest of the language, now what is acceptable there is anything with kind Constraint. Classes like Eq become type constructors with kind * -> Constraint; you apply it to a type like Eq Bool to produce a Constraint. The advantage is now we can use all of the language features for manipulating type-level entities to manipulate constraints (including PolyKinds!).

DataKinds adds the ability to create new user-defined kinds containing new type-level things, in exactly the same way that in vanilla Haskell we can create new user-defined types containing new term-level things. (Exactly the same way; the way DataKinds actually works is that it lets you use a data declaration as normal and then you can use the resulting type constructor at either the type or the kind level)

There are also kinds used for unboxed/unlifted types, which must not be ever mixed with "normal" Haskell types because they have a different memory layout; they can't contain thunks to implement lazy evaluation, so the runtime has to know never to try to "enter" them as a code pointer, or look for additional header bits, etc. They need to be kept separate at the kind level so that ordinary type variables of kind * can't be instantiated with these unlifted/unboxed types (which would allow you to pass these types that need special handling to generic code that doesn't know to provide the special handling). I'm vaguely aware of this stuff but have never actually had to use it, so I won't add any more so I don't get anything wrong. (Anyone who knows what they're talking about enough to write a brief summary paragraph here, please feel free to edit the answer)

There are probably some others I'm forgetting. But certainly the kind language is richer than the OP is imagining just with the basic Haskell features, and there is much more to it once you turn on a few (quite widely used) extensions.

From the C18 standard in 6.7.2.2:

Each enumerated type shall be compatible with char, a signed integer type, or an unsigned integer type. The choice of type is implementation-defined, but shall be capable of representing the values of all the members of the enumeration.

So yes enum { a } e = 1; is valid. e is a 'integer' type so it can take the value 1. The fact that 1 is not present as an enumeration value is no issue. The enumeration members only give handy identifiers for some of possible values.

The evaluation order of A = B was not specified before c++17, after c++17 B is guaranteed to be evaluated before A, see https://en.cppreference.com/w/cpp/language/eval_order rule 20.

The behaviour of valMap[val] = valMap.size(); is therefore unspecified in c++14, you should use:

I quickly tried out the solution I proposed in the comments:

The problem you've encountered here is due to recycling (not the eco-friendly kind). When applying an operation to two vectors that requires them to be the same length, R often automatically recycles, or repeats, the shorter one, until it is long enough to match the longer one. Your unexpected results are due to the fact that R recycles the vector c("p", "o") to be length 4 (length of the larger vector) and essentially converts it to c("p", "o", "p", "o"). If we compare c("p", "o", "p", "o") and c("p", "o", "l", "o") we can see we get the unexpected results of above:

Contrary to common belief Haskell is quite friendly with respect to problems like that. The real issue is that the array library that comes with GHC is total garbage. Another big problem is that everyone is taught in Haskell to use lists where arrays should be used instead, which is usually one of the major sources of slow code and memory bloated programs. So, it is not surprising that GC takes a long time, it is because there is way too much stuff being allocation. Here is a run on the supplied input for the solution provided below:

I'm not sure if it's the best solution but it's the only method with luck, just uninstall the font in win 10 system.

Go to settings-> choose font setting-> find and click into Cascadia and Cascadia mono-> click uninstall , then it returned to normal for me.

When I uninstalled Cascadia mono it appeared a pop-up and told me it's in use, so I closed my chrome and continued the uninstall action.

Done here.

After adding the second elements with push to the same part of the Hash, the elment is now an array. Best you can see this by print the Hash before the crash: