atomic -- low-level atomic values

Atomic values can be used for communication between threads in a safe
way.

blocking_mutate -- a variant of mutate that may be shared between threads

This mutate ensure exclusive access to shared memory via using locks and
blocking.

Accidental race accesses are not permitted by this mutate, i.e., accessing
mutable elements, e.g, via `get` or `put` on a mutable var `mutate.new T`,
are not permitted unless we are in code run via
`blocking_mutate.this.exclusive`.

a Channel can be used to send values
to another thread

NYI: UNDER DEVELOPMENT: max buf size

A Future is an interface for an asynchronous computation.

an interface for a receive only Channel

an interface for a send only Channel

concur.sync -- synchronization primitives
NYI: sync should probably be an effect

type for a spawned thread

NYI: UNDER DEVELOPMENT: rename as `Thread` since this is a `ref`!

Thread_Handler -- abstract source of concurrency

simple, fixed size thread pool

threads -- effect that provides concurrent thread

lifecycle: While effect is installed, threads can be spawned.
When the threads effect is uninstated all threads are joined.

create a String from this instance. Unless redefined, `a.as_string` will
create `"instance[T]"` where `T` is the dynamic type of `a`

dynamic_apply -- apply `f.call` to `Any.this`'s dynamic type and value

This can be used to perform operation on values depending on their dynamic
type.

Here is an example that takes a `Sequence Any` that may contain boxed values
of types `i32` and `f64`. We can now write a feature `get_f64` that extracts
these values converted to `f64` and build a function `sum` that sums them up
as follows:

Get the dynamic type of this instance. For value instances `x`, this is
equal to `type_of x`, but for `x` with a `ref` type `x.dynamic_type` gives
the actual runtime type, while `type_of x` results in the static
compile-time type.

There is no dynamic type of a type instance since this would result in an
endless hierarchy of types. So for Type values, dynamic_type is redefined
to just return Type.type.

convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.

simple, fixed size thread pool

use `concur.thread_pool.env.submit` to
submit a task to the thread_pool.

string representation of this type to be used for debugging.

result has the form "Type of '<name>'", but this might change in the future

There is no dynamic type of a type instance since this would result in an
endless hierarchy of types, so dynamic_type is redefined to just return
Type.type here.

Is this type assignable to a type parameter with constraint `T`?

The result of this is a compile-time constant that can be used to specialize
code for a particular type.


it is most useful in conjunction with preconditions or `if` statements as in


or

name of this type, including type parameters, e.g. 'option (list i32)'.

convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.

NYI: Redefinition allows the type feature to be distinguished from its normal counterpart, see #3913

Get a type as a value.

This is a feature with the effect equivalent to Fuzion's `expr.type` call tail.
It is recommended to use `expr.type` and not `expr.type_value`.

`type_value` is here to show how this can be implemented and to illustrate the
difference to `dynamic_type`.