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An asynchronous, graph-based execution engine
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lib/reactor/dsl/guard.ex
defmodule Reactor.Dsl.Guard do
@moduledoc """
A struct used to store the `guard` DSL entity.
See `d:Reactor.step.guard`
"""
defstruct __identifier__: nil, description: nil, fun: nil
alias Reactor.Guard
@type t :: %__MODULE__{
__identifier__: any,
description: nil | String.t(),
fun: (Reactor.inputs(), Reactor.context() -> :cont | {:halt, Reactor.Step.run_result()})
}
@doc false
def __entity__,
do: %Spark.Dsl.Entity{
name: :guard,
describe: """
Provides a flexible method for conditionally executing a step, or replacing it's result.
Expects a two arity function which takes the step's arguments and context and returns one of the following:
- `:cont` - the guard has passed.
- `{:halt, result}` - the guard has failed - instead of executing the step use the provided result.
""",
examples: [
"""
step :read_file_via_cache do
argument :path, input(:path)
run &File.read(&1.path)
guard fn %{path: path}, %{cache: cache} ->
case Cache.get(cache, path) do
{:ok, content} -> {:halt, {:ok, content}}
_ -> :cont
end
end
end
"""
],
args: [:fun],
target: __MODULE__,
schema: [
fun: [
type: {:mfa_or_fun, 2},
required: true,
doc: """
The guard function.
"""
],
description: [
type: :string,
required: false,
doc: """
An optional description of the guard.
"""
]
]
}
defimpl Guard.Build do
@doc false
def build(guard) do
{:ok, [%Guard{fun: guard.fun}]}
end
end
end