Wearing the hair shirt Wearing the hair shirt - Microsoft Research

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Modules Haskell has many features that overlap with what ML-style modules offer: – type classes – first class universals and existentials Does Haskell need functors anyway? No: one seldom needs to instantiate <strong>the</strong> same functor at different arguments But Haskell lacks a way to distribute “open” libraries, where <strong>the</strong> client provides some base modules; need module signatures and type-safe linking (e.g. PLT,Knit?). π not λ! Wanted: a design with better power, but good power/weight.
Encapsulating it all data ST s a -- Abstract newRef :: a -> ST s (STRef s a) read :: STRef s a -> ST s a write :: STRef s a -> a -> ST s () runST :: (forall s. ST s a) -> a Stateful computation Pure result sort :: Ord a => [a] -> [a] sort xs = runST (do { ..in-place sort.. })
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Wearing the hair shirt A retrospect
Page 3 and 4:
Haskell is 15 years old (born FPCA
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Timeline Sept 87: kick off Apr 90:
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Reflections on the process The i
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Reflections on process Self-appoin
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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 59 and 60: Is sexy good? Yes! Well typed prog
Page 61 and 62: Destination = F w
Page 63: Modules Porsche High power, but poo
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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