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Fn.py ideas and internals Wednesday, March 27, 13

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Fn.py https://github.com/kachayev/fn.py Wednesday, March 27, 13

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About me • Alexey Kachayev • CTO at KitApps Inc. • Open source activist • Functional programming advocate • Erlang, Python, Scala, Clojure, Go, Haskell • @kachayev • github.com/kachayev • kachayev at gmail.com Wednesday, March 27, 13

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About Python • minimalistic syntax • dynamically typed • imperative (by design) • “multi paradigm” • functions are variables • lambdas • iterators, generators, decorators, ... • mutable data types (mostly) Wednesday, March 27, 13

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About Fn.py • enjoy FP in Python • developed on my own talks materials • not only proof of concept • tremendous support from community Wednesday, March 27, 13

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Overview • Scala-style lambdas • Stream and infinite sequences declaration • TCO / trampolines • Itertools recipes • Option monad • Python 2/3 unification for functional stuff Wednesday, March 27, 13

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Scala-style lambdas Wednesday, March 27, 13

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Wednesday, March 27, 13

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Scala-style lambdas Wednesday, March 27, 13

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Scala-style lambdas Wednesday, March 27, 13

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Why? • Code readability • Improve you vision • Keyboard will work longer Wednesday, March 27, 13

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How? • _Callable class • shortcut instance • overloaded operators • each instance - unary or double-side operations tree Wednesday, March 27, 13

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Streams and infinite sequences Wednesday, March 27, 13

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What? • Lazy evaluated list • Composable producers • Any number of consumers • All consumers share one iterable origin • Infinite (potentially) sequence Wednesday, March 27, 13

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Wednesday, March 27, 13

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So what? Wednesday, March 27, 13

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Haskell Wednesday, March 27, 13

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Clojure Wednesday, March 27, 13

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Scala Wednesday, March 27, 13

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Python Wednesday, March 27, 13

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Tail call optimization “I don't believe in recursion as the basis of all programming. This is a fundamental belief of certain computer scientists, especially those who love Scheme and like to teach programming by starting with a "cons" cell and recursion.” Guido van Rossum Wednesday, March 27, 13

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Okay.... Wednesday, March 27, 13

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Trampolines unwrap tail calls to while loop Wednesday, March 27, 13

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Recursion = Induction recursion = induction basis + step while loop = induction basis + step Wednesday, March 27, 13

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Trampoline Wednesday, March 27, 13

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Control flow patterns Wednesday, March 27, 13

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Scala-style Option Wednesday, March 27, 13

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What? • analog = list with 1 or 0 elements • functor + fmap • monadic flatMap operation • “retry” computations Wednesday, March 27, 13

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When? • computations that may fail • heavy execution branching (if/else/try/etc) Wednesday, March 27, 13

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Where to find more? https://github.com/kachayev/fn.py Wednesday, March 27, 13

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Questions? http://kachayev.github.com/talks Wednesday, March 27, 13