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

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​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

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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

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