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bool

bool

bool -- Standard Fuzion type 'bool'

We need to apologize to George Boole for crippling his name a bit,
just to safe us from typing one more letter. But at least we stop
here and do not use boo, bo or similar.

bool is a choice type that can either be true_ of false_.

Note that 'true_' and 'false_' themselves are not of type 'bool'.
Routines 'true' and 'false' are the preferred way to get a constant
value of type 'bool'.

Functions

(R 
type
, F 
type
: Typed_Function R, f F)
 => 
R
[Inherited from  choice]
apply -- apply `f.call` to the value stored in this choice

This can be used to perform operation on values of arbitray choice types.

Example:


which prints

create an option from a lazily evaluated value depending on this bool
 => 
String
[Redefinition of  choice.as_string]
as human readable string
 => 
String
[Inherited from  choice]
create a detailed string from this choice.

This will createa string of the form `type.tag(T,v)` consisting of
the string representations of


So, e.g., `(id (option String) "hi").as_string` will result in
`"option String.0(String,hi)"`
as a trit
(R 
type
, F 
type
: Typed_Combiner R, other choice.this, e R, f F)
 => 
R
[Inherited from  choice]
combine -- if `choice.this` and `other` have the same ordinal number, combine
the value stored in this `ta` and in other `ov` using `f.call va vb`.
Otherwise, return `e`.

This can be used to combine values of arbitrary choice types.
(R 
type
, F 
type
: Typed_Function R, f F)
 => 
R
[Inherited from  Any]
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:


 => 
Type
[Inherited from  Any]
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.
and with eager evaluation
and with lazy evaluation
implies
xor, either or

true if exactly one of the two
bools is true
or with eager evaluation
or with lazy evaluation
 => 
i64
[Inherited from  choice]
Ordinal number corresponding to the index in this choice's open type
parameters of the type of the value stored in this choice.

Note that this is defined even for choices of ambiguous types like
`option nil`: Even though this type may only contain `nil` it can
still be distinguished:


is `0` while


is `1`.
not, negates this boolean
 => 
String
[Inherited from  Any]
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.
(T 
type
, a Lazy T, b Lazy T)
 => 
T
ternary ? : -- NYI: This will be replaced by a more powerful match syntax

Type Features

monoid of bool with infix & operation. Will be true iff all elements are
true.
(B 
type
..., values B...)
 => 
bool
takes an arbitrary amount of bool arguments and returns true if and only if
all of them are true
monoid of bool with infix | operation. Will be false iff all elements are
false.
(B 
type
..., values B...)
 => 
bool
takes an arbitrary amount of bool arguments and returns true if and only if
any of them is true
 => 
String
[Inherited from  Type]
string representation of this type to be used for debugging.

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

redefines:

 => 
Type
[Inherited from  Type]
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.

Note: Typechecking is undecidable when 'type' is a type, Mark B. Reinhold, 1989
see: https://dspace.mit.edu/bitstream/handle/1721.1/149366/MIT-LCS-TR-458.pdf?sequence=6

redefines:

(a bool, b bool)
 => 
bool
[Redefinition of  choice.type.equality]
equality check implementation for inherited property.equatable
create hash code for this instance

This should satisfy the following condition:

(T.equality a b) : (T.hash_code a = T.hash_code b)
(T 
type
)
 => 
bool
[Inherited from  Type]
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

(a choice.this.type, b choice.this.type)
 => 
bool
[Inherited from  choice]
A total order between two choices `a` and `b` is defined only if all element types
of the choice are orderable.
their first elements. If the first `i` element pairs are equal, the order is defined by
the `i+1`th element pair.

This will result in a compile time panic in case any element type is not
orderable.
 => 
String
[Inherited from  Type]
name of this type, including type parameters, e.g. 'option (list i32)'.
monoid of bool with infix ^ operation. Will be true iff an odd number of
elements is true. This gives the even parity.
 => 
String
[Inherited from  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.

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

redefines:

 => 
Type
[Inherited from  Any]
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`.

Applicable universe features

These are features in universe, that have an argument with a type constraint that matches this features type and can therefore be used with it.
(T 
type
:
property.equatable, a T, b T)
 => 
bool
equals -- feature that compares two values using the equality relation
defined in their type
(T 
type
:
property.hashable, a T)
 => 
u64
hash of a value
(T 
type
:
property.equatable, a T, b T)
 => 
bool
infix = -- infix operation as shorthand for 'equals'
(T 
type
:
property.orderable, a T, b T)
 => 
bool
does this come strictly before other?
infix <= -- infix operation as shorthand for 'lteq'
(T 
type
:
property.orderable, a T, b T)
 => 
order
three-way comparison between this and other.

result is < 0 if this < other
result is > 0 if this > other
result is = 0 if this = other
(T 
type
:
property.equatable, a T, b T)
 => 
bool
infix = -- infix operation as shorthand for 'equals'
(T 
type
:
property.orderable, a T, b T)
 => 
bool
does this come strictly after other?
(T 
type
:
property.orderable, a T, b T)
 => 
bool
does this come after other?
is `a` contained in `Set` `s`?

This should usually be called using type inference as in

is `a` not contained in `Set` `s`?

This should usually be called using type inference as in

infix ≤ -- infix operation as shorthand for 'lteq'
(T 
type
:
property.orderable, a T, b T)
 => 
bool
does this come after other?
(T 
type
:
property.orderable, a T, b T)
 => 
order
three-way comparison between this and other.

result is < 0 if this < other
result is > 0 if this > other
result is = 0 if this = other
(T 
type
:
property.partially_orderable, a T, b T)
 => 
bool
lteq -- feature that compares two values using the lteq relation
defined in their type
(T 
type
:
property.orderable, a T, b T)
 => 
T
maximum of two values
memoize `f`.
wraps f so that f will only be called once for every unique input.

The term "memoization" was coined by Donald Michie in 1968 and
is derived from the Latin word "memorandum" ("to be remembered"),
usually truncated as "memo" in American English, and thus carries
the meaning of "turning a function into something to be remembered".
https://en.wikipedia.org/wiki/Memoization

example:

(T 
type
:
property.orderable, a T, b T)
 => 
T
minimum of two values
0.099dev (GIT hash a68bce9af280552faedee34cd5433dc10b6454de)
last changed: 2026-10-14