CODEWITHSUNDEEP
haskelltype-conversion
user3595342
user3595342

Reputation:

Is there a way to convert function type in haskell?

I am fairly new to haskell and I run into this problem with type converting a function. Let's say I don't know anything about a function other than its function type. Is it possible to convert its function type and put it as a new function. For example

myfunc:: (Int -> Int -> Int) -> (Integer -> Integer -> Integer)
myfunc inputfunc = (function with type (Integer -> Integer -> Integer))

Are there ways to do such a thing?

Upvotes: 2

Views: 1118

Answers (2)

Emil
Emil

Reputation: 2167

As already explained by others, what you want is basically this:

convert f x y = fromIntegral (f (fromIntegral x) (fromIntegral y))

This is pretty straightforward. However, if I were to do it, I'd take advantage of the on function from Data.Function, which converts the inputs of functions that take two arguments before applying it. So, in your example, it would look like this:

convert f x y = fromIntegral ((f `on` fromIntegral) x y)

I, personally, would go one step further and make this function point-free, but because on f fromIntegral expects two arguments, you can't just use (.), so I usually define an operator for this:

(.:) = (.) . (.)

You can figure out why this works on your own if you'd like, but now I can define convert as this:

convert f = fromIntegral .: (f `on` fromIntegral)

I feel that this is a lot more readable, but I am biased because I have been coding Haskell like this for a while now.

Also, if you look at the inferred type of this variable, you'd see that it's much more general than what you wanted:

 convert :: (Integral a, Integral a1, Num b, Num b1) = (b1 -> b1 -> a) -> a1 -> a1 -> b

Anyway, I hope this is somewhat useful.

I really don't mean for this post to intimidate you as a newcomer, so if any of it confuses you, please ask me questions and I'd happily answer :)

Upvotes: 1

Christopher King
Christopher King

Reputation: 10941

Hints:

  • (Int -> Int -> Int) -> (Integer -> Integer -> Integer) can also be written (Int -> Int -> Int) -> Integer -> Integer -> Integer. It is a function of three arguments.

  • Converting Numbers

Upvotes: 2

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