# `Skuld.Comp.IInstall`
[🔗](https://github.com/mccraigmccraig/skuld/blob/main/lib/skuld/comp/i_install.ex#L1)

Behaviour for effects supporting handler installation via catch clauses.

This enables bare module patterns in `catch` clauses to install handlers:

    comp do
      x <- State.get()
      x * 2
    catch
      State -> 0   # calls State.__handle__(comp, 0)
    end

## Example

    defmodule State do
      @behaviour Skuld.Comp.IInstall

      @impl Skuld.Comp.IInstall
      def __handle__(comp, initial), do: with_handler(comp, initial)
    end

## Config Interpretation

Effects can accept different config shapes:

    # Simple value
    def __handle__(comp, initial), do: with_handler(comp, initial)

    # Tuple with options
    def __handle__(comp, {initial, opts}), do: with_handler(comp, initial, opts)

    # Keyword options
    def __handle__(comp, opts) when is_list(opts), do: with_handler(comp, opts)

    # Ignored config (e.g., Throw just needs to be installed)
    def __handle__(comp, _config), do: with_handler(comp)

## See Also

- `Skuld.Comp.IHandle` - for effect operation handling
- `Skuld.Comp.IIntercept` - for catch clause value interception

# `__handle__`

```elixir
@callback __handle__(
  comp :: Skuld.Comp.Types.computation(),
  config :: term()
) :: Skuld.Comp.Types.computation()
```

Install a handler for this effect, wrapping the computation.

The `config` term is effect-specific. Effects interpret it flexibly:

- `State.__handle__(comp, initial)` - initial state value
- `Reader.__handle__(comp, env_value)` - reader environment
- `Throw.__handle__(comp, _)` - ignores config
- `Fresh.__handle__(comp, :uuid7)` - handler variant selector

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