I just released Spek, a boolean expression engine based on the one written for LetMe 2.0.0.
Features
- Expression structs and builder functions for boolean logic:
AllOf,AnyOf,Not,Literal,Check. - Evaluation of boolean expressions with optional early stopping and optional evaluation tree output.
- Optimization of boolean expressions using boolean algebra transformation.
- Macros for concisely defining reusable check functions.
The readme is quite comprehensive, so let me just post some code examples here.
Defining a check module
defmodule DeviceChecks do
import Spek.Macros
defcheck device_online(device, reason: :device_offline) do
device.online?
end
defcheck battery_above_20(device, reason: :battery_too_low) do
device.battery_level > 20
end
defcheck charging(device) do
device.charging?
end
defcheck low_power_mode_enabled(device) do
device.low_power_mode?
end
end
(The use of the defcheck macro is optional.)
Composing, optimizing, and evaluating expressions
iex> import Spek
iex> battery_safe =
...> all_of([
...> DeviceChecks.device_online_check(),
...> DeviceChecks.battery_above_20_check()
...> ])
iex> charging_safe =
...> all_of([
...> DeviceChecks.device_online_check(),
...> DeviceChecks.charging_check()
...> ])
iex> rule =
...> any_of([
...> battery_safe,
...> charging_safe,
...> DeviceChecks.low_power_mode_enabled_check()
...> ])
%Spek.AnyOf{
children: [
%Spek.AllOf{
children: [
%Spek.Check{
module: DeviceChecks,
fun: :device_online,
args: [:ctx]
},
%Spek.Check{
module: DeviceChecks,
fun: :battery_above_20,
args: [:ctx]
}
]
},
%Spek.AllOf{
children: [
%Spek.Check{
module: DeviceChecks,
fun: :device_online,
args: [:ctx]
},
%Spek.Check{
module: DeviceChecks,
fun: :charging,
args: [:ctx]
}
]
},
%Spek.Check{
module: DeviceChecks,
fun: :low_power_mode_enabled,
args: [:ctx]
}
]
}
iex> rule = optimize(rule)
%Spek.AnyOf{
children: [
%Spek.AllOf{
children: [
%Spek.Check{
module: DeviceChecks,
fun: :device_online,
args: [:ctx]
},
%Spek.AnyOf{
children: [
%Spek.Check{
module: DeviceChecks,
fun: :battery_above_20,
args: [:ctx]
},
%Spek.Check{
module: DeviceChecks,
fun: :charging,
args: [:ctx]
}
]
}
]
},
%Spek.Check{
module: DeviceChecks,
fun: :low_power_mode_enabled,
args: [:ctx]
}
]
}
iex> device = %{
...> online?: true,
...> battery_level: 12,
...> charging?: false,
...> low_power_mode?: false
...> }
iex> Spek.eval?(rule, device)
false
iex> device = %{
...> online?: false,
...> battery_level: 25,
...> charging?: false,
...> low_power_mode?: false
...> }
iex> Spek.eval_tree(rule, device)
{
:error,
%Spek.EvaluationError{
expression: %Spek.AnyOf{
children: [
%Spek.AllOf{
satisfied?: false,
children: [
%Spek.Check{
module: DeviceChecks,
fun: :device_online,
args: [:ctx],
result: {:error, :device_offline},
satisfied?: false
}
]
},
%Spek.Check{
module: DeviceChecks,
fun: :low_power_mode_enabled,
args: [:ctx],
result: {:error, :failed},
satisfied?: false
}
],
satisfied?: false
},
message: "rule evaluation failed"
}
}
Feedback
Your feedback is appreciated, especially when it comes to API design or feature ideas.
What may come in a future release:
- Serialization/deserialization of expressions
- Extract errors of an evaluated expression into a list of error reasons
. I have a question: when and what to use this library for?
