# Writer


Append-only output effect: tell/tellAll with list-collecting handler.

## `handler`

_writer.handler: collects tell/tellAll output as a list in handler state, starting at `[]`; pair with `trampoline.handle`._

Standard writer handler. Collects tell output in state as a list.
Initial state: `[]`

```nix
handle { handlers = writer.handler; state = []; } comp
```

## `tell`

_tell: append a single value to the writer effect's output log; impure request resuming with null._

```
tell : w -> Computation null
```

Append a value to the output log.

## `tellAll`

_tellAll: append a list of values to the writer effect's output log in a single impure request; one bind instead of N from mapping tell._

```
tellAll : [w] -> Computation null
```

Append a list of values to the output log.