∃ PROLOG |PROLOG ∈ SCALA

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∃ PROLOG | PROLOG ∈ SCALA

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About me: @folone like types* *same reasons why @propensive does in his “Batshit crazy algebra with types” talk

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def validate[F[_], G, H, V <: HList, I <: HList, M <: HList, A <: HList, R](g: G)(v: V)(implicit hlG: FnHListerAux[G, A => R], zip: ZipApplyAux[V, I, M], mapped: MappedAux[A, F, M], unH: FnUnHListerAux[I => F[R], H], folder: LeftFolderAux[M, F[A => R], applier.type, F[HNil => R]], appl: Applicative[F]) = unH((in: I) => folder(zip(v, in), hlG(g).point[F]).map(_(HNil)))

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8+ implicits FnHipsterAux

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LOGIC PROGRAMMING

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PROgrammation en LOGique, 1972, 5GL Lingua franca

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— Alan J. Perlis A language that doesn't aﬀect the way you think about programming, is not worth knowing.

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BURAN

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IBM Watson http://www.ibm.com/smarterplanet/us/en/ibmwatson/developercloud/services-catalog.html

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Main principles It's all about formulating the question. Facts (ground terms) Rules (to generate more facts) RELATIONS > FUNCTIONS WHAT > HOW

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PREDICATES > FUNCTIONS Map inputs to outputs Run Return some output Deﬁne constraints Match Only return yes or no* *If "yes", they may add bindings to variables. log(2, 16, 4). log(2, 16) = 4

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How many PROLOG programmers does it take to change a lightbulb? —

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NO.

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PACKAGE MANAGER

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Facts depends(scala, java). depends(java, gcc). depends(ghc, clang). depends(erlang, prolog). depends(erlang, clang). depends(prolog, gcc).

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?- depends(scala, prolog). no ?- depends(java, gcc). yes ?- depends(prolog, X). X = gcc. ?- depends(erlang, X). X = prolog ; X = clang. Questions

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Questions ?- depends(What, OnWhat). What = scala, OnWhat = java; What = java, OnWhat = gcc; What = ghc, OnWhat = clang; What = erlang, OnWhat = prolog; What = erlang, OnWhat = clang; What = prolog, OnWhat = gcc.

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common_dep(Pack1, Pack2) :-   depends(Pack1, Topic),   depends(Pack2, Topic),   Pack1 \== Pack2. ?- common_dep(java, What).  What = prolog. Rules

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Facts provides(scala, scalac). provides(scala, scala). provides(erlang, erl). provides(java, javac). provides(prolog, swipl). provides(ghc, ghci).

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deps_needed(Package, What) :- depends(Package, What). deps_needed(Package, What) :- depends(Package, X), depends(X, What).

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?- deps_needed(scala, What). What = java ; What = gcc. Questions

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deps_to_run(Command, What) :- provides(What, Command). deps_to_run(Command, What) :- provides(X, Command), deps_needed(X, What). Rules

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?- deps_to_run(erl, What). What = erlang ; What = prolog ; What = clang ; What = gcc. Questions

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install(Dep) :- installed(Dep). install(Dep) :- assert(installed(Dep)), write('Installing '), write_term(Dep, []), write('\n'), installed(Dep).

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run(Command) :- findall(Dep, deps_to_run(Command, Dep), L), reverse(L, Deps), forall(member(Dep, Deps), install(Dep)), write('Running '), write_term(Command, []), write('\n'), !.

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?- run(ghci). Installing clang Installing ghc Running ghci true. ?- run(erl). Installing gcc Installing prolog Installing erlang Running erl true.

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github.com/larsyencken/marelle

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Functional is imperative without state. Logic is functional without manual search*. * DFS

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Scala is a logic programming language...

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In type system. programming language...

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In type system. programming in Scala is... TYPELEVEL

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logic programming in Scala programming in Scala is...

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gcd(X, X, X). gcd(X, Y, Out) :- X < Y Z is Y - X gcd(X, Z, Out). gcd(X, Y, Out) :- Y < X, gcd(Y, X, Out). Prolog

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Facts — implicit vals. Rules — implicit defs taking implicit vals as parameters. Implication is the other way around.

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The more interesting your types get, the less fun it is to write them down. – Benjamin Pierce —

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• Scala does not perform the DFS. In case of multiple implicits, it does not compile. Prioritizing implicits via inheritance. • Diverging implicit expansion -Xlog-implicits. • Extremely hard to debug (pen and paper style). • Peculiar exceptions (SO in compiler, Method too large, etc.) Gotchas

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So now I need to redeﬁne all the goodness from prolog stdlib?! Lists, naturals, etc. Shapeless: stdlib for logic programming in scala. —

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DEMO github.com/folone/2014-scalaio

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Functional in the small, OO in the large, logic in the type system!

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Promoting Functions to Type Families in Haskell HMonoid, HFunctor, HApplicative, HMonad Related Fun with type functions The art of Prolog Shapeless