vars

replace effect in the current context by this and abort current execution

does this effect support abort?

Redefining this to return `false` helps to detect unexptected calls to
`abort` at runtime and ensure that the static analysis finds that the
code executed with this effect will always return normally and produce
a result. This is used, e.g, in `mutate` to avoid static analysis
reporting `panic` as an effect of the use of a local mutate instance.

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

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 hierachy of types. So for Type values, dynamic_type is redefined
to just return Type.type.

If set, get the environment variable corresponding to v.

If set, get the environment variable corresponding to v.
Otherwise, return default

install this effect and run code that produces a result of
type T. panic in case abort is called.

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.

abort the current execution and return from the surrounding call to
abortable with result == false.

execute the code of 'f' in the context of this effect

Set the environment variable corresponding to n to have the
value v.

This will overwrite the value of the environment variable, if
it is set already.

Unset the environment variable corresponding to n.

This will also return success (unit) if the variable was not
set anyway.

install this simple_effect and run code

In case of an `abort`, `use` returns silently (NYI: maybe this should better
return an oucome with the abort wrapped in an error?).

has an effect of the given type been installed?

has an effect of the given type been installed?

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`.