What Lies Under The Syntax Sugar

Presentation given at the October 2017 WebDevTalks Meetup.

In this talk I explore the similarities and differences in the implementations of the 3 programming languages that I use the most these days: Objective-C, Swift and Elixir.

This talk is a deep dive into what goes behind the scenes when code is compiled.

Transcript

1. W H AT L I E S U N D E R T H E S Y N TA X S U G A R W D T O C T O B E R
2. Oscar Swanros Sr. iOS Software Engineer @ CloudApp oscar@swanros.com @Swanros W H O A M I
3. P R O G R A M M I N G L A N G U A G E S
7. Compiled Open source Widespread use Fun to write Completely different approaches
8. Compiled Open source Dynamic Statically checked at compile time Runs on the BEAM
10. Compiled Open source Dynamic Statically checked at compile time Runs on Linux, macOS, iOS, watchOS, tvOS, Raspberry Pi, Android, etc etc et
12. Compiled Open source SUPER Dynamic The compiler tries to catch many things Runs wherever C code runs*
15. R U N T I M E
16. [object doSomething]; objc_msgSend(object, doSomething); [object doSomethingWith:@“Param”]; objc_msgSend(object, doSomething, @“Param”);
17. id objc_msgSend(id self, SEL op, …); id: any Objective-C object type SEL: typedef struct objc_selector *SEL;
21. LLVM
22. LLVM
23. Objective-C/C++/C
24. Objective-C/C++/C LLVM Intermediate Representation
25. unsigned square_int(unsigned a) { return a * a } define i32 @square_unsigned(i32 %a) { %l = mul i32 %a, %a ret i32 %l }
26. IR is a low-level programming language in it of itself, that LLVM knows how to interpret and optimize.
28. Objective-C is a relatively thin layer on top of C. Most of the actual code is still C. Swift is a completely new language, that drops the baggage of C. The whole Swift stdlib is written in Swift.
31. A S T
32. let x = 1 let y = 2 let z = 3 * x + y
36. S E M A ( S E M A N T I C A N A LY S I S )
37. S E M A ( S E M A N T I C A N A LY S I S ) • Perform type checking
38. S E M A ( S E M A N T I C A N A LY S I S ) • Perform type checking • Unused variables?
39. S E M A ( S E M A N T I C A N A LY S I S ) • Perform type checking • Unused variables? • Check for unreachable code
40. S E M A ( S E M A N T I C A N A LY S I S ) • Perform type checking • Unused variables? • Check for unreachable code • Overflow checks
41. S I L G E N / S I L (Swift intermediate Language)
44. S I L • Represents program semantics • Is suitable as a base for code generation and further analysis/optimizations • Bridges Swift sources and LLVM.
46. B U I LT I N S • Builtins represent types and operations below Swift, at LLVM level. • Swift stlib implements interfaces on top of Builtins for ease of use. • Great for portability. Swift only cares about Int, the LLVM backend defines what an Int actually is.
47. A F T E R S I L G E N • SIL is further analyzed, optimized. • LLVM IR is generated. • IR is passed to the swiftc LLVM backend to generate executables.
48. E L I X I R ?
49. With Swift/Objective-C
50. Once compilation starts, there’s no turning back. With Swift/Objective-C
51. Once compilation starts, there’s no turning back. AST is not accessible to the program. With Swift/Objective-C
52. E L I X I R I S D I F F E R E N T
53. 9 9 % O F E L I X I R I S B U I LT I N E L I X I R
55. W H Y I S T H I S G O O D ? • The language only has to comply with a very small list of characteristics. • As long as the general structure of the language remains, changes can occur rather rapidly. • Elixir is some sort of Erlang DSL (but not quite).
56. E L I X I R C O M P I L AT I O N • Read file • Tokens • Parse, build initial AST • Expand macros • Apply rewrite rules • Lower Elixir AST to Erlang AST • Pass to Erlang compiler…
57. E R L A N G C O M P I L AT I O N • Compile Erlang AST to Core AST • Core optimization and inlining • Pattern matching • Optimize kernel • Generate ASM • Optimize ASM • Generate Bytecode • Write .beam
58. • Flexible at compile time • Efficient • A really nice syntax for a rather powerful underlying
 engine • Distributed by nature
59. • Flexible at compile time • Compiles really quickly (because the compiler can 
 only do so much). • Cumbersome syntax • Super powerful runtime
60. • Really strict at compile time, misuse of language 
 features results in compile errors. • Compilation is really slow, but final program is way
 safer in terms of memory management • Familiar syntax • The amount of optimizations that go into compiling
 Swift, make it really fast.
61. TA K E A WAY S • A language is much more than just its syntax • The foundation and background of each language is important • Knowing where they break give you superpowers • Knowing how to break them give you really good insights • Is really fun to work with compilers
62. T H A N K S !
63. Q U E S T I O N S ? O S C A R @ S WA N R O S . C O M