Funx.Predicate.Dsl.Behaviour behaviour (funx v0.8.0)

Behaviour for custom predicate logic in the Predicate DSL.

Implement this behaviour to define reusable predicates that can be used with on directives in the DSL.

This is useful for teams that want to create reusable, configurable predicates without repeating logic across the codebase.

Basic Example

defmodule IsActive do
  @behaviour Funx.Predicate.Dsl.Behaviour

  @impl true
  def pred(_opts) do
    fn user -> user.active end
  end
end

# In DSL
use Funx.Predicate

pred do
  on IsActive  # Checks if active
end

With Options

defmodule HasMinimumAge do
  @behaviour Funx.Predicate.Dsl.Behaviour

  @impl true
  def pred(opts) do
    minimum_age = Keyword.get(opts, :minimum, 18)

    fn user -> user.age >= minimum_age end
  end
end

# In DSL
pred do
  on HasMinimumAge, minimum: 21
end

Why Use This?

Reusable: Define predicates once, use everywhere
Configurable: Built-in support for options
Testable: Predicates can be unit tested independently
Discoverable: All predicates in one module namespace

The returned predicate is a function (any() -> boolean()) that will be composed with other predicates using the DSL's combinator logic.

Summary

Callbacks

pred(opts)

Returns a predicate function.

Callbacks

pred(opts)

@callback pred(opts :: keyword()) :: Funx.Predicate.t()

Returns a predicate function.

Takes options and returns a predicate function (any() -> boolean()).

Arguments

opts - Keyword list of options passed from the DSL

Return Value

A predicate function with the signature:

(any() -> boolean())

Examples

# Simple predicate
def pred(_opts) do
  fn user -> user.active end
end

# With options
def pred(opts) do
  field = Keyword.get(opts, :field, :active)
  fn item -> Map.get(item, field) end
end

# Complex logic
def pred(opts) do
  min_age = Keyword.get(opts, :min_age, 18)
  max_age = Keyword.get(opts, :max_age, 65)

  fn user ->
    user.age >= min_age and user.age <= max_age
  end
end

Most implementations return simple predicate functions that check specific conditions on the input value.