Wearing the hair shirt Wearing the hair shirt - Microsoft Research

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Sexy types Haskell has become a laboratory and playground for advanced type hackery Polymorphic recursion Higher kinded type variables data T k a = T a (k (T k a)) Polymorphic functions as constructor arguments data T = MkT (forall a. [a] -> [a]) Polymorphic functions as arbitrary function arguments (higher ranked types) f :: (forall a. [a]->[a]) -> ... Existential types data T = exists a. Show a => MkT a
Is sexy good? Yes! Well typed programs don’t go wrong Less mundanely (but more allusively) sexy types let you think higher thoughts and still stay [almost] sane: – deeply higher-order functions – functors – folds and unfolds – monads and monad transformers – arrows (now finding application in real-time reactive programming) – short-cut deforestation – bootstrapped data structures
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Wearing the hair shirt A retrospect
Page 3 and 4:
Haskell is 15 years old (born FPCA
Page 5 and 6:
Timeline Sept 87: kick off Apr 90:
Page 7 and 8: Reflections on the process The i
Page 9: Reflections on process Self-appoin
Page 12 and 13: Syntactic redundancy Seductive ide
Page 14 and 15: “Expression style” Define a fun
Page 16 and 17: Example (ICFP02 prog comp) Pattern
Page 18 and 19: What really matters?
Page 20 and 21: But... Laziness makes it much, muc
Page 22: Combinator libraries Recursive valu
Page 25 and 26: Monadic I/O A value of type (IO t)
Page 27 and 28: Connecting I/O operations (>>=) ::
Page 29 and 30: Control structures Values of type (
Page 31 and 32: Monads Exceptions type Exn a = E
Page 33 and 34: The IO monad The IO monad allows
Page 35 and 36: What have we achieved? ...without
Page 37 and 38: Open challenge 1 Open problem: the
Page 39 and 40: Monad summary Monads are a beautif
Page 41 and 42: What really matters? Laziness Purit
Page 44 and 45: Type classes class Eq a where (==)
Page 46 and 47: Type classes over time Type classe
Page 48 and 49: Quickcheck propRev :: [Int] -> Bool
Page 50 and 51: Extensiblity Like OOP, one can add
Page 52 and 53: Type-based dispatch class Num a whe
Page 54 and 55: Cool generalisations Multi-paramet
Page 56: Type classes summary A much more f
Page 61 and 62: Destination = F w
Page 63 and 64: Modules Porsche High power, but poo
Page 65 and 66: Encapsulating it all data ST s a --
Page 67 and 68: Shirts off to Wadler Type classes
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Wearing the hair shirt Wearing the hair shirt - Microsoft Research

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