Bridging the Language Gap

Given at Craft Conference 2017 in Budapest

Transcript

1. BRIDGING THE LANGUAGE GAP SAMUEL GIDDINS
2. SAMUEL GIDDINS > Bundler > CocoaPods > RubyGems > Realm > Trill
3. I work on lots of random projects across many communities.
4. I write developer tools that occasionally work. Otherwise, I'm in a library at UChicago, studying something impractical.
5. THE LANGUAGE GAP Hi, me llamo ש ָׁ ל וֹ ם .
6. THE LANGUAGE GAP Gap a break in continuity Bridge something that is intended to reconcile or form a connection between two things
7. THE LANGUAGE GAP > When we want to connect two or more languages to each other. > When we make languages talk to each other.
8. Some languages can be translated perfectly: > Curry–Howard correspondence > Relationship between propositions & proofs and values & types > Turing machines > Turing completeness > !
9. But for most, something is lost in translation
10. WHY BOTHER?
11. WHY BOTHER? Every language has strengths & weaknesses
12. Every language has a library of knowledge that is useful to refer to
13. Is this sounding familiar?
14. LANGUAGES > Ruby > Objective-C > Swift > C++ > ...
15. WAYS TO TRANSLATE > Importer > FFI > XPC > Compiler Support > main()
16. WAYS TO TRANSLATE Some are like Google Translate. They work on everything, but not very well. Some are like a paid translator. Amazing at going between exactly 2 languages, but very expensive.
17. The Google Translate of Programming Language Translation
18. $ echo I have earned those names. Bought and paid for them. I have earned those names. Bought and paid for them.
19. The command line (or shell). Spawn a process, pass these arguments to main().
20. > No context > No ongoing communication > Universal on any POSIX system
21. HOW SHELL PROGRAMS WORK TOGETHER > 1 Program, 1 Process > Program Arguments > environ(7) > exit(3) > Side Effects
22. A very general way of allowing programs in different languages to work together. But they don't work together very well.
23. So, what's a step better than Google Translate?
24. The Stack Overflow of Programming Language Translation
25. > Run into a problem > Google it > Click on the first SO link > Copy-paste the solution that's already written
26. FFI THE STACK OVERFLOW OF PROGRAMMING LANGUAGE TRANSLATION
27. FOREIGN FUNCTION INTERFACE Matches the ABI of the calling language with that of the language being called.
28. ABI > How functions call each other > How data is laid out in memory > How memory is managed across function calls
29. A "simple" example
30. swift.swift func fib(_ x: Int) -> Int { guard x >= 1 else { fatalError("fib of a non-positive number is undefined, use Γ instead") } if x == 1 || x == 2 { return 1 } return fib(x - 1) + fib(x - 2) } c.c #include <stdio.h> int _TF5swift3fibFSiSi(int); int main(int argc, char *argv[]) { for (int i = 1; i < 15; ++i) { printf("fib(%d) = %d\n", i, _TF5swift3fibFSiSi(i)); } }
31. Arcane Commands > clang c.c -c > swiftc swift.swift -c -parse-as-library > ld swift.o c.o ... -o main > ./main
32. It works! fib(1) = 1 fib(2) = 1 fib(3) = 2 fib(4) = 3 fib(5) = 5 fib(6) = 8 fib(7) = 13 fib(8) = 21 fib(9) = 34 fib(10) = 55 fib(11) = 89 fib(12) = 144 fib(13) = 233 fib(14) = 377
33. FFI is brittle
34. We relied on us knowing how the Swift program worked under the hood in order to call it from C.
35. Now imagine writing out those function prototypes for an entire library. And remember, a single mistake means !.
36. XPC THE ADULT APPROACH TO main()
37. CROSS PROCESS COMMUNICATION
38. > Some context > Ongoing communication > Incredibly system dependent
39. XPC OPTIONS > Sockets > HTTP > Mach XPC
40. They all work by sharing ❇ state ❇ across processes.
41. This is where the world of microservices fits in
42. Standardized data formats like JSON, protobuf, GraphQL, etc make this much less painful
43. But containerization is complicated, and introduces complexities beyond the language gap
44. </hot take>
45. As you can imagine, I'm still not a huge fan.
46. COMPILER ✨
47. This is the good kind of magic, I promise.
48. This is like seeing inside the matrix. It's being able to call the name of the wind when your app encounters danger.
49. Teach one compiler how to understand the structure of multiple languages.
50. Think C headers.
51. Now, imagine you're not even writing C...
52. Header: void print_the_thing(const char*); Swift: print_the_thing("the thing!")
53. Remember the FFI ! above? We get all those benefits without any work
54. No work no bugs
55. The compiler isn't smarter. It's just as smart as the people who know all the intricacies of all the languages.
56. Think memory management. Call conventions.
57. In my free time, I work on a language called Trill
58. // ClangImporter.swift class ClangImporter { func run(in context: ASTContext) { importBuiltinAliases(into: context) importBuiltinFunctions(into: context) importDeclarations(for: URL(fileURLWithPath: ClangImporter.runtimeHeaderPath). appendingPathComponent("trill.h").path, in: context) if let path = ClangImporter.includeDir { for header in ClangImporter.headerFiles { importDeclarations(for: "\(path)/\(header)", in: context) } } } }
59. // ClangImporter.swift class ClangImporter { func importDeclarations(for path: String, in context: ASTContext) { do { let file = try SourceFile(path: .file(URL(fileURLWithPath: path)), context: context) context.add(file) } catch { // do nothing } let tu: CXTranslationUnit do { tu = try translationUnit(for: path) } catch { context.error(error) return } let cursor = clang_getTranslationUnitCursor(tu) clang_visitChildrenWithBlock(cursor) { child, parent in let kind = clang_getCursorKind(child) switch kind { case CXCursor_TypedefDecl: self.importTypeDef(child, in: context) case CXCursor_EnumDecl: self.importEnum(child, in: context) case CXCursor_StructDecl: self.importStruct(child, in: context) case CXCursor_FunctionDecl: self.importFunction(child, in: context) case CXCursor_MacroDefinition: self.importMacro(child, in: tu, context: context) case CXCursor_UnionDecl: self.importUnion(child, context: context) case CXCursor_VarDecl: self.importVariableDeclation(child, in: tu, context: context) default: break } return CXChildVisit_Continue } clang_disposeTranslationUnit(tu) } }
60. This is super ✨ meta ✨
61. The Swift compiler knows how to import C headers The Trill compiler is written in Swift It uses a C compiler to read C headers
62. But the result is a nearly seamless experience for users
63. let foo = 10 let bar = garbage() func garbage() -> Int { printf("%s called!\n", #function) trill_printStackTrace() return 100 } func main() { printf("Garbage hasn't been called yet\n") printf("Foo: %d, bar: %d\n", foo, bar) printf("Bar: %d\n", bar) }
64. That's Trill code. Calling C code.
66. It takes a lot of work to implement the magic
67. But that work creates the sort of seamless experience we expect in today's world of many languages.
68. If I can understand C, and Swift, and Ruby and Python... Why shouldn't all of them understand each other?
69. Building bridges capable of carrying all this traffic is hard But you reap the benefits every day
70. Back to the top: We work in multiple languages for a good reason
71. We're most productive when we can pick & choose the best tool for the job at hand
72. That happens most often and with the least friction when our languages can talk with each other
73. Just like in human language, speaking happens in many different ways
74. And choosing the right way to translate is just as important with machines as with people
75. So, the answer with programming languages is the same as with upset people
76. BUILD A BRIDGE
77. BUILD A BRIDGE AND GET OVER IT
78. [insert obligatory Bridges of Siracusa County reference here]
80. In which Samuel answers random questions about language interop & bridging
81. @segiddins