CODEWITHSUNDEEP
haskellfunctional-programming
devoured elysium
devoured elysium

Reputation: 105037

How to run a sequence of operations (functions) in Haskell?

Let's say I have a list of values to which I want to apply a sequence of operations until I get a final result:

[0, 1, 2]

firstOperation xs = map (+1) xs
secondOperation xs = filter even xs
thirdOperation xs = sum xs

Although I am sure there are other better ways to handle this, the only one I currently know is to define a function that calls all these functions nested one inside another:

runAllOperations xs = thirdOperation (secondOperation (firstOperation xs))

but this is both ugly and raises the problem that if I have 10 operations, turns this bit of code into a maintanance nightmare.

What is the correct way of implementing something of the kind here? Keep in mind the example I gave above is just a oversimplification of what I am facing on my current project.

Upvotes: 2

Views: 3247

Answers (2)

oino
oino

Reputation: 121

. or $ are way more readable than ( and )

runAllOperations xs = thirdOperation $ secondOperation $ firstOperation xs

or

runAllOperations = thirdOperation . secondOperation . firstOperation

Upvotes: 6

Anon.
Anon.

Reputation: 59963

If you can make a list of all the operations, you can then fold the composition operator over that list:

foldr (.) id fns

Then you can apply the result of that to the initial values.

Though you might need to apply a final reduction step separately.

Upvotes: 4

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