View Source Skitter.DSL.Component (Skitter v0.5.0)
Callback and Component definition DSL.
This module offers macros to define component modules and callbacks. Please refer to the
documentation of defcomponent/3
.
Link to this section Summary
Functions
Updates the current state.
Emit value
to port
Emit several values to port
Obtain the component configuration.
Define a callback.
Define a component module.
Read the current value of a field stored in state.
Obtain the current state.
Defines the initial state of a component.
Creates an initial struct-based state for a component.
Link to this section Functions
Updates the current state.
This macro should only be used inside the body of defcb/2
. It updates the current value of the
component state to the provided value.
This macro can be used in two ways: it can be used to update the component state or a field of
the component state. The latter option can only be used if the state of the component is a
struct (i.e. if the intial state has been defined using state_struct/1
). The former options
modifies the component state as a whole, the second option only modifies the value of the
provided field stored in the component state.
Examples
defcomponent WriteExample do
defcb write(), do: state <~ :foo
end
iex> Component.call(WriteExample, :write, nil, nil, []).state
:foo
defcomponent FieldWriteExample do
state_struct [:field]
defcb write(), do: field <~ :bar
end
iex> Component.call(FieldWriteExample, :write, %FieldWriteExample{field: :foo}, nil, []).state.field
:bar
defcomponent WrongFieldWriteExample do
fields [:field]
defcb write(), do: doesnotexist <~ :bar
end
iex> Component.call(WrongFieldWriteExample, :write, %WrongFieldWriteExample{field: :foo}, nil, [])
** (KeyError) key :doesnotexist not found in: %Skitter.DSL.ComponentTest.WrongFieldWriteExample{field: :foo}
Emit value
to port
This macro is used to specify value
should be emitted on port
. This means that value
will be sent to any components downstream of the current component. This macro should only be
used inside the body of defcb/2
. If a previous value was specified for port
, it is
overridden.
Examples
defcomponent SingleEmitExample do
defcb emit(value) do
value ~> some_port
:foo ~> some_other_port
end
end
iex> Component.call(SingleEmitExample, :emit, [:bar]).emit
[some_other_port: [:foo], some_port: [:bar]]
Emit several values to port
This macro works like ~>/2
, but emits several output values to the port instead of a single
value. Each value in the provided Enumerable.t/0
will be sent to downstream components
individually.
Examples
defcomponent MultiEmitExample do
defcb emit(value) do
value ~> some_port
[:foo, :bar] ~>> some_other_port
end
end
iex> Component.call(MultiEmitExample, :emit, [:bar]).emit
[some_other_port: [:foo, :bar], some_port: [:bar]]
Obtain the component configuration.
This macro reads the current value of the configuration passed to the component callback when
it was called. It should only be used inside the body of defcb/2
.
Examples
defcomponent ConfigExample do
defcb read(), do: config()
end
iex> Component.call(ConfigExample, :read, []).result
nil
iex> Component.call(ConfigExample, :read, :config, []).result
:config
iex> Component.call(ConfigExample, :read, :state, :config, []).result
:config
Define a callback.
This macro is used to define a callback function. Using this macro, a callback can be defined
similar to a regular procedure. Inside the body of the procedure, ~>/2
, ~>>/2
<~/2
and
sigil_f/2
can be used to access the state and to emit output. The macro ensures:
The function returns a
Skitter.Component.result/0
with the correct state (as updated by<~/2
), emit (as updated by~>/2
and~>>/2
) and result (which contains the value of the last expression inbody
).Skitter.Component._sk_callback_info/2
andc:Skitter.Callback._sk_callbacks/0
of the component module contains the required information about the defined callback.
Note that, under the hood, defcb/2
generates a regular elixir function. Therefore, pattern
matching may still be used in the argument list of the callback. Attributes such as @doc
may
also be used as usual.
Examples
defcomponent CbExample do
defcb simple(), do: nil
defcb arguments(arg1, arg2), do: arg1 + arg2
defcb state(), do: counter <~ (~f{counter} + 1)
defcb emit_single(), do: ~D[1991-12-08] ~> out_port
defcb emit_multi(), do: [~D[1991-12-08], ~D[2021-07-08]] ~>> out_port
end
iex> Component.callbacks(CbExample)
#MapSet<[arguments: 2, emit_multi: 0, emit_single: 0, simple: 0, state: 0]>
iex> Component.callback_info(CbExample, :simple, 0)
%Info{read?: false, write?: false, emit?: false}
iex> Component.callback_info(CbExample, :arguments, 2)
%Info{read?: false, write?: false, emit?: false}
iex> Component.callback_info(CbExample, :state, 0)
%Info{read?: true, write?: true, emit?: false}
iex> Component.callback_info(CbExample, :emit_single, 0)
%Info{read?: false, write?: false, emit?: true}
iex> Component.callback_info(CbExample, :emit_multi, 0)
%Info{read?: false, write?: false, emit?: true}
iex> Component.call(CbExample, :simple, %{}, nil, [])
%Result{result: nil, emit: [], state: %{}}
iex> Component.call(CbExample, :arguments, %{}, nil, [10, 20])
%Result{result: 30, emit: [], state: %{}}
iex> Component.call(CbExample, :state, %{counter: 10, other: :foo}, nil, [])
%Result{result: nil, emit: [], state: %{counter: 11, other: :foo}}
iex> Component.call(CbExample, :emit_single, %{}, nil, [])
%Result{result: nil, emit: [out_port: [~D[1991-12-08]]], state: %{}}
iex> Component.call(CbExample, :emit_multi, %{}, nil, [])
%Result{result: nil, emit: [out_port: [~D[1991-12-08], ~D[2021-07-08]]], state: %{}}
Define a component module.
This macro is used to define a component module. Using this macro, a component can be defined
similar to a normal module. The macro will enable the use of defcb/2
and provides
implementations for Skitter.Component._sk_component_info/1
,
Skitter.Component._sk_component_initial_state/0
, Skitter.Component._sk_callbacks/0
and Skitter.Component._sk_callback_info/2
.
Component strategy and ports
The component Strategy and its in -and out ports can be defined in the header of the component declaration as follows:
iex> defcomponent SignatureExample, in: [a, b, c], out: [y, z], strategy: SomeStrategy do
...> end
iex> Component.strategy(SignatureExample)
SomeStrategy
iex> Component.in_ports(SignatureExample)
[:a, :b, :c]
iex> Component.out_ports(SignatureExample)
[:y, :z]
If a component has no in
, or out
ports, they can be omitted from the component's header.
Furthermore, if the component only has a single in
or out
port, the list notation can be
omitted:
iex> defcomponent PortExample, in: a do
...> end
iex> Component.in_ports(PortExample)
[:a]
iex> Component.out_ports(PortExample)
[]
The strategy may be omitted. In this case, a strategy must be provided when the defined component is embedded inside a workflow. If this is not done, an error will be raised when the workflow is deployed.
Examples
defcomponent Average, in: value, out: current do
state_struct total: 0, count: 0
defcb react(value) do
total <~ ~f{total} + value
count <~ ~f{count} + 1
~f{total} / ~f{count} ~> current
end
end
iex> Component.in_ports(Average)
[:value]
iex> Component.out_ports(Average)
[:current]
iex> Component.strategy(Average)
nil
iex> Component.call(Average, :react, [10])
%Result{result: nil, emit: [current: [10.0]], state: %Average{count: 1, total: 10}}
iex> Component.call(Average, :react, %Average{count: 1, total: 10}, nil, [10])
%Result{result: nil, emit: [current: [10.0]], state: %Average{count: 2, total: 20}}
Documentation
When writing documentation for a component, @componentdoc
can be used instead of the usual
@moduledoc
. When this is done, this macro will automatically add additional information about
the component to the generated documentation.
Read the current value of a field stored in state.
This macro expects that the current component state is a struct (i.e. it expects a component
that uses state_struct/1
), and reads the current value of field
from the struct.
This macro should only be used inside the body of defcb/2
.
Examples
defcomponent FieldReadExample do
state_struct field: nil
defcb read(), do: ~f{field}
end
iex> Component.call(FieldReadExample, :read, %FieldReadExample{field: 5}, nil, []).result
5
iex> Component.call(FieldReadExample, :read, %FieldReadExample{field: :foo}, nil, []).result
:foo
Obtain the current state.
This macro reads the current value of the state passed to the component callback when it was
called. It should only be used inside the body of defcb/2
.
Examples
defcomponent ReadExample do
state 0
defcb read(), do: state()
end
iex> Component.call(ReadExample, :read, []).result
0
iex> Component.call(ReadExample, :read, :state, nil, []).result
:state
iex> Component.call(ReadExample, :read, :state, nil, []).result
:state
Defines the initial state of a component.
This macro is used to define the initial state of a component. This state is passed to every
called callback when no state is provided by the component's strategy. When this macro is not
used, the initial state of a component is nil
.
Internally, this macro generates a definition of
Skitter.Component._sk_component_initial_state/0
.
Examples
defcomponent NoStateExample do
defcb return_state, do: state()
end
defcomponent StateExample do
state 0
defcb return_state, do: state()
end
iex> Component.initial_state(NoStateExample)
nil
iex> Component.initial_state(StateExample)
0
iex> Component.call(NoStateExample, :return_state, []).state
nil
iex> Component.call(StateExample, :return_state, []).state
0
iex> Component.call(NoStateExample, :return_state, :some_state, nil, []).state
:some_state
iex> Component.call(StateExample, :return_state, :some_state, nil, []).state
:some_state
Creates an initial struct-based state for a component.
In Elixir, it is common to use a struct to store structured information. Therefore, when a component manages a complex state, it often defines a struct and uses this struct as the initial state of the component. Afterwards, the state of the component is updated when it reacts to incoming data:
defcomponent Average, in: value, out: current do
defstruct [total: 0, count: 0]
state %__MODULE__{}
defcb react(val) do
state <~ %{state() | count: state().count + 1}
state <~ %{state() | total: state().total + val}
state().total / state().count ~> current
end
end
In order to streamline the use of this pattern, this macro defines a struct and uses this struct
as the initial state of the component. Moreover, the sigil_f/2
and ~>/2
macros are designed
to be used with structs, enabling them to read the state and update it:
defcomponent Average, in: value, out: current do
state_struct total: 0, count: 0
defcb react(val) do
count <~ ~f{count} + 1
total <~ ~f{total} + val
~f{total} / ~f{count} ~> current
end
end
The second example generates the code shown in the first example.
Examples
iex> Component.initial_state(Average)
%Average{total: 0, count: 0}