Haskell: I/O and Returning From a Function

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In most functional languages, this would work. However, Haskell is a pure functional language. You are not allowed to do IO in functions, so the function can either be

  1. [Int] -> [Int] without performing any IO or
  2. [Int] -> IO [Int] with IO

The type of dot as inferred by the compiler is dot :: (Show t) => [t] -> IO [t] but you can declare it to be [Int] -> IO [Int]:

dot :: [Int] -> IO [Int]

See IO monad: http://book.realworldhaskell.org/read/io.html

I haven’t mentioned System.IO.Unsafe.unsafePerformIO that should be used with great care and with a firm understanding of its consequences.

More Related Contents:

  1. A Haskell function of type: IO String-> String
  2. Should do-notation be avoided in Haskell?
  3. Converting IO Int to Int
  4. In what sense is the IO Monad pure?
  5. What is the monomorphism restriction?
  6. What is a monad?
  7. Monads with Join() instead of Bind()
  8. What is the purpose of Rank2Types?
  9. Wrong IO actions order using putStr and getLine
  10. How do you represent a graph in Haskell?
  11. Haskell types frustrating a simple ‘average’ function
  12. Difference between `data` and `newtype` in Haskell
  13. Is Haskell truly pure (is any language that deals with input and output outside the system)?
  14. Euler 43 – is there a monad to help write this list comprehension?
  15. Why does haskell’s bind function take a function from non-monadic to monadic
  16. Expressing do block using only monadic bind syntax
  17. Why do we need monads?
  18. Difference between Monad and Applicative in Haskell
  19. Defining a new monad in haskell raises no instance for Applicative
  20. Typeclass constraints on data declarations
  21. What is a monad?
  22. Is there a way to place some impure code inside pure functions?
  23. Why is there “data” and “newtype” in Haskell? [duplicate]
  24. Why are side-effects modeled as monads in Haskell?
  25. How to interpret bind/>>= of the function instance?
  26. Why should Applicative be a superclass of Monad?
  27. Turning A => M[B] into M[A => B]
  28. Given a Haskell type signature, is it possible to generate the code automatically?
  29. How to return a pure value from a impure method
  30. Return specific type within Haskell

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