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outcome
outcome
Type Parameters
Functions
returns o if outcome is ok, otherwise return the outcome's own
error.
error.
synonym for infix >>=
this switch as an equatable_switch
converts switch into a list of either a single element in case
switch.this.exists or `nil`otherwise
switch.this.exists or `nil`otherwise
convert this switch to an option
convert this to an outcome
this is essentially a no-op.
this is essentially a no-op.
convert this switch to an outcome
converts outcome to a string
returns the result of T.as_string for a successful outcome, or
"--$e--" for e error.
returns the result of T.as_string for a successful outcome, or
"--$e--" for e error.
monadic operator
This enables a very idiomatic way of error handling: assume you are trying
to read 42 bytes from a file into a string. Let open be a feature that takes
a file name and returns an outcome of some abstract file descriptor, let read
be a feature that takes an abstract file descriptor and a number of bytes to
read and returns an outcome of a byte (u8) array. We want to read 42 bytes
from a file called "example.txt" into a string, and we wrap this into an outcome,
for handling the case that an error occurs when opening the file (i.e. it does
not exist) or when reading the file (i.e. example.txt is not actually a file but
a directory). Using match expressions, this is very cumbersome:
The monadic operator turns this into:
This enables a very idiomatic way of error handling: assume you are trying
to read 42 bytes from a file into a string. Let open be a feature that takes
a file name and returns an outcome of some abstract file descriptor, let read
be a feature that takes an abstract file descriptor and a number of bytes to
read and returns an outcome of a byte (u8) array. We want to read 42 bytes
from a file called "example.txt" into a string, and we wrap this into an outcome,
for handling the case that an error occurs when opening the file (i.e. it does
not exist) or when reading the file (i.e. example.txt is not actually a file but
a directory). Using match expressions, this is very cumbersome:
The monadic operator turns this into:
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.
error of an outcome that is known to contain an error
This can only be called in cases where it is known for sure that this
outcome is an error. A runtime error will be created otherwise.
This can only be called in cases where it is known for sure that this
outcome is an error. A runtime error will be created otherwise.
Does this switch contain a value of type A?
unwraps a switch that is known to contain a value
this can only be called in cases where it is known for sure that this switch
is not nil. A runtime error will be created otherwise.
this can only be called in cases where it is known for sure that this switch
is not nil. A runtime error will be created otherwise.
unwrap value or get default
monadic operator
(B type, MB type:monad (monad.infix >>=~.B) (monad.infix >>=~.MB), f Unary MB monad.A) => MB[Inherited from monad][Abstract feature][Contains abstract features]¶
(B
type
, MB type
:monad (monad.infix >>=~.B) (monad.infix >>=~.MB), f Unary MB monad.A) =>
MB[Inherited from monad]
[Abstract feature]
[Contains abstract features]
¶monadic operator to another monad
Apply f to elements of type A and wrap them in MB.
Apply f to elements of type A and wrap them in MB.
join operator
Does this switch contain a value of type A?
if this switch is nil return the result of f
otherwise just return this switch.
otherwise just return this switch.
get A or cause an `exception T`
unwraps an switch if it exists, returns default value otherwise.
short-hand postfix operator for '!exists'
short-hand postfix operator for 'exists'
short-hand prefix operator for '!exists'
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.
value of a switch that is known to contain a value
This can only be called in cases where it is known for sure that this
switch is not a B. A runtime error will be created otherwise.
This can only be called in cases where it is known for sure that this
switch is not a B. A runtime error will be created otherwise.
value of a switch or default if switch contains B
Type Functions
string representation of this type to be used for debugging.
result has the form "Type of '<name>'", but this might change in the future
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.
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.
is_of_integer_type(n T : numeric) => T : integer
say (is_of_integer_type 1234) # true
say (is_of_integer_type 3.14) # false
it is most useful in conjunction preconditions or `if` statements as in
pair(a,b T) is
same
pre T : property.equatable
=>
a = b
or
val(n T) is
The result of this is a compile-time constant that can be used to specialize
code for a particular type.
is_of_integer_type(n T : numeric) => T : integer
say (is_of_integer_type 1234) # true
say (is_of_integer_type 3.14) # false
it is most useful in conjunction preconditions or `if` statements as in
pair(a,b T) is
same
pre T : property.equatable
=>
a = b
or
val(n T) is
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
return function
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`.
0.094dev (2025-06-18 15:08:51 GIT hash 89cffc23ae669b0898a5564fefbf793fcb8e5ca7 built by fridi@fzen)
outcome is a choice type that represents the result of a routine that
may either produce something useful or fail producing an error condition.
Several error conditions are needed if there are several very different
reasons for an operation to fail, e.g.
get_data (u User, t Type) outcome data IO_Error Permission_Error is
if u.allowed_to_access T
(read_file t.file_name)?
else
Permission_Error u, t
read_file t Type outcome data IO_Error is
[..]
Note that 'outcome data IO_Error' is not assignment compatible with
'outcome data IO_Error Permission_Error', it has to be unwrapped first.
This unwrapping, however, requires very little boilerplate, it is done
using the '?' on the result of the call to 'read_file': This unwraps
'outcome data IO_Error' into 'IO_Error', which would be returned abruptly,
and 'data', which would be returned normally. Both are assignment
compatible to 'outcome data IO_Error Permission_Error', so everything
is fine.