# `Journey.Node.Conditions`

This module contains helper functions for use when defining upstream dependencies for `compute` modules.

# `false?`

This is a helper function provided for use in `unblocked_when` conditions.
This function checks if the upstream node's value is `false`.

## Examples

```elixir
iex> import Journey.Node
iex> import Journey.Node.Conditions
iex> import Journey.Node.UpstreamDependencies
iex> graph = Journey.new_graph(
...>   "umbrella forecast graph, doctest for false?",
...>   "v1.0.0",
...>   [
...>     input(:it_will_rain_tomorrow),
...>     compute(
...>       :todays_preparation,
...>       unblocked_when(:it_will_rain_tomorrow, &false?/1),
...>       fn %{it_will_rain_tomorrow: false} -> {:ok, "prepare my bike"} end
...>     )
...>   ]
...> )
iex> execution = Journey.start_execution(graph)
iex> execution = Journey.set(execution, :it_will_rain_tomorrow, false)
iex> {:ok, "prepare my bike"} = Journey.get_value(execution, :todays_preparation, wait: :any)
iex> execution = Journey.set(execution, :it_will_rain_tomorrow, true)
iex> Journey.get_value(execution, :todays_preparation)
{:error, :not_set}

```

# `provided?`

This is a helper function provided for use in `unblocked_when` conditions.
This function checks if the supplied node has a value.
For "scheduled" types of nodes (`tick_once`, `tick_recurring`) it also checks that the scheduled time has come.

## Examples

```elixir
iex> import Journey.Node
iex> import Journey.Node.Conditions
iex> import Journey.Node.UpstreamDependencies
iex> graph = Journey.new_graph(
...>   "greeting workflow, doctest for provided?",
...>   "v1.0.0",
...>   [
...>     input(:name),
...>     compute(
...>       :greeting,
...>       unblocked_when(:name, &provided?/1),
...>       fn %{name: name} -> {:ok, "Hello, #{name}!"} end
...>     )
...>   ]
...> )
iex> execution = Journey.start_execution(graph)
iex> execution = Journey.set(execution, :name, "Alice")
iex> {:ok, "Hello, Alice!"} = Journey.get_value(execution, :greeting, wait: :any)
```

# `true?`

This is a helper function provided for use in `unblocked_when` conditions.
This function checks if the upstream node's value is `true`.

## Examples

```elixir
iex> import Journey.Node
iex> import Journey.Node.Conditions
iex> import Journey.Node.UpstreamDependencies
iex> graph = Journey.new_graph(
...>   "umbrella forecast graph, doctest for true?",
...>   "v1.0.0",
...>   [
...>     input(:it_will_rain_tomorrow),
...>     compute(
...>       :umbrella,
...>       unblocked_when(:it_will_rain_tomorrow, &true?/1),
...>       fn %{it_will_rain_tomorrow: true} -> {:ok, "need to pack my umbrella"} end
...>     )
...>   ]
...> )
iex> execution = Journey.start_execution(graph)
iex> execution = Journey.set(execution, :it_will_rain_tomorrow, true)
iex> {:ok, "need to pack my umbrella"} = Journey.get_value(execution, :umbrella, wait: :any)
iex> execution = Journey.set(execution, :it_will_rain_tomorrow, false)
iex> Journey.get_value(execution, :umbrella)
{:error, :not_set}

```

---

*Consult [api-reference.md](api-reference.md) for complete listing*