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Using Generators in Gall

Throughout the basic course, we have mostly typed pokes in the form:

:chanel &chanel-action [%increase-counter step=9]

Gall has support for routing input to generators before passing it to the agent, and we can use this to make the above agent interactions cleaner. This particularly helps for agents that users will access via the Dojo.

Gall Generator Mechanics

Let's take an example with the s3-store agent. We can poke it like so:

:s3-store|set-endpoint 'myendpoint.com'

The above expands to "poke %s3-store with the output from calling +s3-store/set-endpoint 'myendpoint.com'." This is similar to how marks look for marks like chanel-action in mar/chanel/action.hoon.

The output is passed to on-poke of s3-store as [mark data].

Example: gen/s3-store/set-endpoint.hoon

Open the file gen/s3-store/set-endpoint.hoon. Its code (as of this writing) is:

/-  *s3
:-  %say
|=  $:  [now=@da eny=@uvJ =beak]
        [[endpoint=@t ~] ~]
    ==
:-  %s3-action
^-  action
[%set-endpoint endpoint]

The arguments to this %say generator are:

  1. [now=@da eny=@uvJ =beak], the normal environment variables passed to a %say generator.
  2. [endpoint=@t ~], a list of arguments
  3. ~: this generator takes no optional arguments

In our example of :s3-store|set-endpoint 'myendpoint.com', the generator takes 'myendpoint.com' as the first argument, and evaluates it to [%s3-action [%set-endpoint endpoint]].

We can check this at the Dojo by running the generator directly:

> +s3-store/set-endpoint 'myendpoint.com'
[%set-endpoint endpoint='myendpoint.com']

Notice that the Dojo automatically applies the mark to the data and removes the mark: this is a normal %say generator; no magic.

Raw | Commands

In the dojo, any command like |reset or |commit is simply a shortcut for :hood|reset or :hood|commit. The hood generator is run, and then the hood agent processes the result.

To see the commands available to hood and the variables for those commands, just browse the gen/hood directory. Each generator file represents a command, and you can open the files to see the exact sample that each command takes.

Example: |commit

When we run |commit %home, that calls the generator gen/hood/commit.hoon with argument %home. It returns a cell like so:

:- %kiln-commit
[mon auto]

So a %home argument returns [%kiln-commit [%home %.n]]. We can check this in the Dojo:

> +hood/commit %home
[%home %.n]

If run as |commit, the whole [%kiln-commit [%home %.n]] is passed as [mark vase] to the on-poke of hood, from whence it is passed to lib/hood/kiln.hoon. There, the mark is matched and handled.

Summary

You can make these simple generators for your own applications quite easily. Just follow the approach of `s3-store` above, and you can make separate `|` commands for all the actions you want your users to perform from the Dojo.