Here is a data definition for a data type called TrafficLight.

TrafficLight $=$ Enum$(\text{'}$TrafficLight$\text{'},[\text{'}$red$\text{'},$ 'yellow', 'green'$])$

# interp. a traffic light is either red, yellow or green

# examples are redundant for enumerations

@typecheck

def fn$\_$for$\_$traffic$\_$light$($tl: TrafficLight$)->...$:

# template based on Enumeration

if tl $==$ TrafficLight.red:

return $...$

elif tl $==$ TrafficLight.yellow:

return $...$

elif tl $==$ TrafficLight.green:

return $...$

Design a function called produce$\_$next$\_$light that takes a TrafficLight and produces the next TrafficLight. Here, we'll assume that the traffic light has the expected behaviour of transitioning from red to green to yellow to red, etc.

Note that the data definition we provided above does not solve the problem. The "function" defined there is actually a template function: it's the "skeleton" of what any function that operates on a TrafficLight will likely do$,$ but without any details filled in$.$

To use a data definition, put it in a cell above the one where you're designing your function. Do not edit it$,$ as that is not required to solve this problem. To use a template function $($to design a function that takes a parameter whose type is from that data definition$),$ you copy and paste it at the templating stage of the How to Design Functions recipe.

Name Type Description

produce$\_$next$\_$light python function Function to design