Rules

A rule has three fields:

name: shown in the navigator and the change log.
when: a DSL expression that is true or false. Leave it blank and the rule always runs.
do: what happens when when is true. A DSL expression or a CodeBlock (see that chapter).

A simple rule

name:  eat_grass
when:  patch().grass > 0
do:    energy = energy + 4; patch().grass = 0

Toggling a rule

Every rule has an enabled switch. A disabled rule stays in the navigator but does not run. Use it to compare a model with and without that rule.

Scopes recap

setup_rules: run once at Setup. No self.
go_rules: run once per tick for the whole model. No self.
agent_type.rules: run for each agent. self is the current agent.
patches.rules: run for each patch. self is the current patch.