Compose Functions

Computer Science Level pending

Consider a higher order function applyAll that takes in a list of functions and a value and applies all the functions sequentially on the value.

For example,

applyAll [f,g,h] x = f (g (h x))

Which of the following higher order functions would be useful to define such an applyAll ?

map fold zip filter

Agnishom Chattopadhyay by Agnishom Chattopadhyay , 22, India

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1 solution

Notice that we are attempting to create a function by composing all the functions.

Hence, we could define this with fold 

1
2
 
applyAll :: [(a -> a)] -> a -> a
applyAll fs x = (foldr (.) id fs)  x

Or simply, 

1
 
applyAll = foldr (.) id

0 Helpful 0 Interesting 0 Brilliant 0 Confused

You could use foldr1 directly without the use of the identity function. 

1
 
applyAll = foldr1 (.)

A Former Brilliant Member - 4 years, 9 months ago

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Interesting, what does foldr1 do?

Agnishom Chattopadhyay - 4 years, 9 months ago

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