choice
choice
Type Parameters
Functions
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
This can be used to perform operation on values of arbitray choice types.
Example:
which prints
create a string from this choice.
This will use the value stored stored in this choice and create its String
representation using `prefix $` and return that without any additional
information.
This will use the value stored stored in this choice and create its String
representation using `prefix $` and return that without any additional
information.
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)"`
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)"`
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.
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.
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:
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.
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.
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`.
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`.
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.
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.
Type Features
string representation of this type to be used for debugging.
result has the form "<name>", but this might change in the future
result has the form "<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.
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
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
equality of two choices `a` and `b` is defined only if all element types
of the choice are equatable. The choices are equal if they have the same
ordinal number and the contained values are equal.
This will result in a compile time panic in case any element type is not
equatable.
of the choice are equatable. The choices are equal if they have the same
ordinal number and the contained values are equal.
This will result in a compile time panic in case any element type is not
equatable.
create hash code for this choice
This should satisfy the following condition:
(T.equality a b) : (T.hash_code a = T.hash_code b)
This will result in a compile-time `panic` in case any element type is not hashable.
This should satisfy the following condition:
(T.equality a b) : (T.hash_code a = T.hash_code b)
This will result in a compile-time `panic` in case any element type is not hashable.
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
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[Redefinition of property.partially_orderable.type.lteq]¶
(a choice.this.type, b choice.this.type)
=>
bool[Redefinition of property.partially_orderable.type.lteq]
¶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.
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.
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
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`.
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.
equals -- feature that compares two values using the equality relation
defined in their type
defined in their type
hash of a value
infix = -- infix operation as shorthand for 'equals'
does this come strictly before other?
infix <= -- infix operation as shorthand for 'lteq'
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
result is < 0 if this < other
result is > 0 if this > other
result is = 0 if this = other
infix = -- infix operation as shorthand for 'equals'
does this come strictly after other?
does this come after other?
is `a` contained in `Set` `s`?
This should usually be called using type inference as in
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
This should usually be called using type inference as in
infix ≤ -- infix operation as shorthand for 'lteq'
does this come after other?
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
result is < 0 if this < other
result is > 0 if this > other
result is = 0 if this = other
lteq -- feature that compares two values using the lteq relation
defined in their type
defined in their type
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:
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:
minimum of two values
0.099dev (GIT hash a68bce9af280552faedee34cd5433dc10b6454de)
choice types provide algebraic sum types of all the generic arguments
provided to choice. A instance of a choice type is a tagged union of
the types provided as actual generic type parameters. This concept is
also called variant, sum type or coproduct in other contexts.
Syntactic sugar of the Fuzion language permits an alternative notation
for choice types with actual generics as follows
which is equivalent to
The parser will directly convert the first notation into a choice type
with actual generics.
A field of choice type can be assigned a value of the same choice type
or of any of the actual generic type parameters provided to the choice
feature.
Two choice types choice A B and choice B A that differ only in the order
of their actual generic arguments are treated as different types.
Named choice types can be constructed through inheritance, i.e.,
creates a choice type of A and B with the name C. Two named choice types
D and E that inherit from choice with the same actual generic arguments in
the same order are nevertheless different types and their values are not
assignable to one another.
Named choice types may declare or inherit additional inner features as long
as these features are not fields. Also, declared inner features must not
build a closure that accesses outer features. Additional parents must be
unit types, i.e., they must not declare fields nor access features of any
of their outer features.
Note that all types provided must be distinct, it is not possible to
repeat the same type as in choice i32 i32 or float | float. If a sum
type of two or more equal types is desired, these types must first be
wrapped into a new type as illustrated in the following example:
Say we want to store a temperature that is given as a 32 bit integer
in degrees centigrade or degrees Fahrenheit. So we define two wrapper
features
Now we define the choice type using the wrapped i32 types, which are
distinct:
When passing arguments to this feature, we need to wrap them accordingly:
When matching the choice type, we use the wrapper types and access the
argument field 'degrees' to access the i32 stored inside
NYI: Once Fuzion's match expression supports destructuring as well, we should
be able to extract the degrees directly as in
A choice type with no actual generic arguments is isomorphic to 'void', i.e, it
is a type that has an empty set of possible values.