Functor and Applicative Quiz

Functors

and

Applicatives

​Functor

• ​Generalisation of `map` for other types

• ​Applying functions into a context

• ​Structure preserving

• ​Once you understand it, you will always know the behaviour of fmap for any Functor, without needing to know the implementation!

​Using InstanceSigs

extension

Fill in the Blank

What is the value of xs?

(Make sure to remove all spaces, no advanced matching option sadly)

Fill in the Blank

What is the value of xs?

(Make sure to remove all spaces)

Fill in the Blank

What is the value of x?

Fill in the Blank

What is the value of y?

Fill in the Blank

What is the value of t?

​Applicative

• <*>

  • Applying functions within a context

  • ​Output structure depends on input structure alone. Values cannot affect structure

• pure

  • ​Lifting values into a context

  • Preserves structure when used with <*>

• ​All Applicatives are also Functors

​Using InstanceSigs

extension

Fill in the Blank

What is the value of x? (the second one)

Multiple Select

If the only information we have about a type is that it has an Applicative instance, what do we automatically know about it?

• We know it also has a Functor instance

• We know how <*> will produce new structure

• We know what its structure looks like

• We know a way to create a value of that type

• We know we can sequence values of that type and combine their results

Multiple Select

Which of the following are true statements?

• For a particular type, only one kind of Applicative behaviour is possible

• For a particular type, only one kind of Functor behaviour is possible

• For a particular type, it cannot have more than one Applicative behaviour simultaneously

• Applicative is strictly more 'powerful' than Functor

• All Functors are also Applicatives

Fill in the Blank

How many elements does xs have?