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Haskell

Introduction

Raison d’être

  • Haskell was created by a committee that was formed in the FPCA conference of 1987.
  • Its purpose was to unite the functional programming world by being a language that is:
    • Accessible (open-source)
    • Stable
    • Disruptive
    • Useful for teaching, research, as well for real-world applications

Where it is used

Haskell is used in a plethora of fields and industries to solve a variety of problems. For example:

  • The Cardano blockchain platform, its protocol and its smart contract infrastructure
  • In Facebook for filtering spam.
  • Hasura, an open-source real-time GraphQL engine is written in Haskell.

Features

Laziness

  • A very distinctive feature of Haskell is Lazy evaluation.
  • Its usefulness lies in the fact that it delays the computation of an expression until the value of the computation is needed.
  • The efficiency of this operation provides the reduction of unnecessary calculations alongside the saving of time.
  • The downside of this process is that the usage of memory can be unpredictable.

Lambdas

Lambda expressions are a way of defining an anonymous function, helping developers define functions “on the fly” and passing them directly as arguments to other functions.

\arg1 arg2 ... argN -> body
-- Example: Lambda that adds two numbers
\x y -> x + y

Monads

  • Monads allow you to express complex computations in a modular way, granting the ability to represent computations as sequences of steps.
  • It is a type class that defines two operations: return and >>=.
    • The return operation takes a value and puts it in a monad, lifting a pure value into a monadic context.
    • The >>= operation is employed to connect monadic computations together.
main :: IO ()
main = do
    putStrLn "What is your name ?"
    name <- getLine
    putStrLn ("Hello, " ++ name ++ "!")

Memory management

  • Haskell’s ghc implementation uses a parallel generational-copying garbage collector. That means that all memory allocations and releases happen in the background automatically.
  • In every step, Haskell’s GC searches for any live data: Data pointed to by the roots (the stack and any global variables).
  • The live data found are copied to a new heap; Any dead data is discarded.

Prelude

Haskell’s API is represented by its Prelude, a structure which holds a set of standard definitions and is included automatically in all of Haskell’s modules. The definitions include:

  • Functions: map, filter, read
  • Data Types: Int, Bool, Char
  • Type Classes: Eq, Read, Num

Example code

Factorial

  • Here’s a small program that computes the factorial of a given number recursively.
factorial :: Int -> Int
factorial 0 = 1
factorial n = n * factorial (n - 1)
  • Here’s a program that does the same thing by leveraging lambdas.
factorial n = product [1..n]

Thank you!