In this talk I introduce Perl 6 and some of its exciting new features, especially gradual typing, roles and some functional programming features like lazy lists. This talk was given at the Scottish Programming Languages Seminar on 24th Feb 2016 at the School of Computing Science of Glasgow University.

1. It was finally Christmas:
Perl 6 is here!
Wim Vanderbauwhede
School of Compu6ng Science
University of Glasgow

2. “Language is
ideology”
Kress, Gunther, et al. "Language as ideology." (1982).

3. A trip down memory lane

4. 2007

5. • Perl6/Pugs invited talk at POPL 2007
• Audrey Tang had created Pugs, a Perl 6
implementa6on in Haskell
• Perl 6 was promised for "Christmas”
• And there was some delay …

6. Perl 6meline
Dow Jones index, 1985-2015

7. Context
hZp://www.codeeval.com/

8. Context
TIOBE Index for February 2016, hZp://www.6obe.com/
Popularity of programming languages – TIOBE

9. Context
TIOBE Index for February 2016, hZp://www.6obe.com/
Popularity of programming languages – TIOBE

10. Perl
Neil Stephenson, “Cryptonomicon”, p480

11. Perl 5
• Interpreted
• Dynamically typed
• Garbage collec6on
• In that sense very similar to JavaScript,
Python, Ruby, …

12. Perl 5
• Uses funny characters for typing:
$: scalar
@: array (list)
%: hash (dic6onary, map)
&: subrou6ne
• Incorporates a separate language:
regular expressions (PCRE)

13. Perl 5
• But also:
• Lexical scoping
• Higher-order func6ons
• Anonymous func6ons
• Closures

14. Perl 6
• Is a new language, not backward
compa6ble with Perl 5.
• S6ll mostly Perl
• But a modern language

15. Compiler and VM

16. Compiler (Rakudo)
hZps://github.com/rakudo/rakudo

17. VM (MoarVM)
• Meta-object protocol based
• Precise, genera6onal, and parallel GC
• First-class code objects, closures, …
• Excep6ons
• Con6nua6ons
• Threads, mutexes, …
• JIT compila6on
hZps://github.com/MoarVM/MoarVM

18. Grammars

19. Parsing
• Perl 6 has Grammars, Rules, Tokens and Regexes as
part of the language
• Similar to classes but used to organize parsers
• Rules are lexeme parsers
• Tokens are token parsers
• Regexes are PCREs
• Perl 6 is parsed and executed using a Perl 6-style
grammar.

21. Objects

22. JavaScript Python
Objects

23. Perl 6 Objects

24. Perl 6 Objects
Roles

25. Perl 6 Objects
• Accessors for free
• Default constructor
• Inheritance
• Roles (mixins)
• Built on a Meta Object Protocol
• Full introspec6on
• So s6ll nothing special …

26. But wait …

27. Perl 6 Objects

28. Perl 6 Objects

29. Gradual typing!

30. Gradual typing
• By default variables are dynamically typed.
• Explicitly typed variables are sta6cally typed.
• But type checks can be deferred to run 6me.
• Underlying theory:
hZps://github.com/samth/gradual-typing-bib

31. Gradual typing: subsets
• Type constraint checked at run 6me

32. Gradual typing: type capture
• Defer the specifica6on of a type constraint to the
6me the func6on is called.
• Allows to refer to a type both in the signature and
the func6on body.

33. Gradual typing: type capture
• Defer the specifica6on of a type constraint to the
6me the func6on is called.
• Allows to refer to a type both in the signature and
the func6on body.

34. Roles

35. Roles
• Basis for the Perl 6 type system
• Used for composi6on and mixins
• In Perl 6, the “funny characters” are syntax for a set
of predefined roles:
@: Posi6onal (array)
%: Associa6ve (hash)
&: Callable (subrou6ne)
• So …

36. No more funny characters!
• Actually, the “funny characters” are now op6onal:

37. Polymorphic func6ons
• Also known as mul6ple dispatch

38. Polymorphic func6ons
• Also known as mul6ple dispatch

39. Polymorphic func6ons
• Looks familiar?

40. Parametric roles
• Roles that take one or more type variables

41. Possibly Maybe

42. FuncHonal
programming

43. Func6onal features
• Higher-order func6ons
• Anonymous func6ons (lambdas)
• Currying
• Immutable lists, lazy evalua6on
• Tail call op6miza6on
• Op6onal immutable variables

44. Type capture revisited
• Type capture also works with closures and lambdas

45. Lazy lists
• Perl 6 dis6nguishes between sequences, lists and
arrays.
• Sequences are immutable, but are consumed
when iterated.
• Lists are immutable
• Arrays are mutable
• By defaults Seq, List and Array are lazy, but can be
made eager.

46. Seq and List

47. Array

48. Promises

49. Concurrency
• High-level
• Promises (futures)
• Channels
• Supplies
• Low-level
• Threads
• Schedulers
• Locks

50. Promises

51. Conclusion
•

52. Thank you!