Hacking on a Swift Compiler

This is a talk I've presented on Swift Warsaw #6 during MCE Meetup Night 2016.

It tells a story of how I implemented a "unless" keyword by making the parser both aware of the new token and parsing it as a valid if statement.

Transcript

1. Hacking on Swift Compiler Michał Kałużny
 @justMaku
2. Hacking on Swift Compiler Michał Kałużny
 @justMaku I HAVE NO IDEA WHAT I'M DOING:
3. I HAVE NO IDEA WHAT I'M DOING: Typing Random Stuff Till It Compiles Michał Kałużny
 @justMaku
5. - (UIView *)findSuperViewWithClass:(Class)superViewClass { UIView *superView = self.superview; UIView *foundSuperView = nil; while (nil != superView && nil == foundSuperView) { if ([superView isKindOfClass:superViewClass]) { foundSuperView = superView; } else { superView = superView.superview; } } return foundSuperView; }
6. It all started with a single tweet...
7. WELL…
8. L L V
 M
9. Love Lattner
 Very
 Much
10. LLVM
11. So how does this Swift Compiler work?
13. Parse SEMA SILGen AST SIL IRGen IR LLVM .o No, 
 but seriously…
14. SO… 
 You're going to do what?
15. Parse SEMA SILGen AST SIL IRGen IR LLVM .o
16. ANSWER? 
 Well, "unless" is just an opposite of "if", right?
17. Consume the "if" token Parse body Try to consume "else" keyword If it exists, parse "else" body Return IfStmt object
18. makeParserResult(Status, new (Context) IfStmt(LabelInfo, IfLoc, Condition, NormalBody.get(), ElseLoc, ElseBody.getPtrOrNull())); makeParserResult(Status, new (Context) IfStmt(LabelInfo, UnlessLoc, Condition, EmptyBody.get(), UnlessLoc, NormalBody.get()));
19. Consume the "unless" token Parse body Return IfStmt object Create an empty body
20. DEMO 
 TIME
21. Hot takes • Swift's code is well written and properly commented.
23. Hot takes • Swift's code is well written and properly commented. • Compilers are quite complicated.
24. SEMA SIL TOKENIZER LEXER PARSER AST LLVM IR
25. Hot takes • Swift's code is well written and properly commented. • Compilers are quite complicated. • But they're fun to play with!
27. More info • Swift High Level IR: A case study Complementing LLVM IR with Language-Specific Optimization (Joeff Groff & Chris Lattner)
 http://bit.ly/llvm_sil
 • Contributing to Open Source Swift by Jesse Squires
 http://bit.ly/swift_contributing
28. Job opportunity! Disclaimer: Must be willing to relocate to San Francisco.
29. QUESTIONS?
30. THANKS!