Haskell, the most pragmatic functional language

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Haskell Pragmatic Functional Programming

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Nope, we’re busy Not pragmatic dude… Programs  Complexity

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“Haskell is the most pragmatic functional programming language”

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Functional Programming A. Functions (the real ones, aka pure ones) B. Functions as values (higher-order) C. Recursion (the only loop construction)

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Functional Language A. Support for functional abstractions B. Support for handling side-effects C. Efficient (you don’t pay the abstraction)

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Abstraction Side-Effects Efficiency Scala Erlang Haskell

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Abstraction

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Abstraction   Side Effects

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Abstraction   Side Effects Efficiency

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–Gabriel González “Haskell has effects. The difference is that they’re first- class values and not to-the-side”

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How on Earth is Haskell not popular?

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Iron Triangle concise  fast to write efficient  (fast to run) easy  (fast to learn)

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Recursion

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• Is more general • Haskell tail recursive functions in constant time • Haskell mutual recursive functions in constant time (Monads!)

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New types

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New Types • Wrapper evaporates after compilation newtype PK = PrimaryKey Int

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Laziness

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Laziness • Possible to reuse functions foldr = … map = foldr… filter = foldr …

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Type inference

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Type inference • Global type inference

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Deferred type errors/Type holes

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Deferred types • -fdefer-type-errors Type errors are converted to runtime errors (good for ghci sessions) • Type holes put the compiler to work for us main = _

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Dynamic types

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Dynamic types

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Software transactional memory

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STM Haskell is the best language in the world in which to implement an STM • It was originally 100 lines of code, and even now it’s only about 600 lines of C! • It exploits three properties of the language: purity, immutability and laziness • Haskell retries an STM transaction as needed. Immutability allows it to do this fearlessly, and laziness avoids fully evaluating the transaction • STM is harder in other languages. For instance in Clojure you have to manually implement rollback functionality. https://begriffs.com/posts/2016-04-02-software-transactional-memory.html

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Higher-kinded types

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Higher-kinded types class Monad (m :: * -> *) where

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Polymorphic! Higher-kinded types

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Polymorphic! Higher-kinded types data T (a :: k) = …

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Data types type classes (type families)

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Data types type classes (type families) data family XList a data instance XList Char = XCons Char (XList Char) | XNil data instance XList () = XListUnit Int

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Much more • Loops fusion • Dependent types • Functional Reactive Programming • Speed!

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Use Haskell!!!

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return $