Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Optional Type Spe...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Dynamic, but stro...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Dynamic, but stro...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Yes and No :-/

T...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Yes and No :-/

T...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Yes and No :-/

T...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Declaring Types

...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Declaring Types

...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Using Types

-spe...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Using Types

-typ...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Dialyzer and Type...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Dialyzer and Type...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Dialyzer and Type...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Discrepency Analy...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Property tests fr...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Table of Contents...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Conclusion

On it...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Conclusion

On it...
Erlang Type Overview
Can we add compile-time types to Erlang?
Optional Types
Dialyzer
Proper
Conclusion

Conclusion

On it...
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Optional Type Specification in Erlang

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A talk on types in Erlang, presented at Lambda Luminaries on November 11, 2013.

http://www.meetup.com/lambda-luminaries/events/145676142/

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Optional Type Specification in Erlang

  1. 1. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Optional Type Specification in Erlang Andreas Pauley – @apauley Lambda Luminaries – @lambdaluminary November 11, 2013 Andreas Pauley – @apauley Types in Erlang
  2. 2. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  3. 3. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Dynamic, but strong example({}) -> "empty tuple"; example(List) when is_list(List) -> length(List); example(_Else) -> another_return_type. Andreas Pauley – @apauley Types in Erlang
  4. 4. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Dynamic, but strong 3> 5 + "6". ** exception error: an error occurred when evaluating an arithmetic expression in operator +/2 called as 5 + "6" Andreas Pauley – @apauley Types in Erlang
  5. 5. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  6. 6. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Yes and No :-/ The Haskell giants Simon Marlow and Philip Wadler spent over a year developing a static type system for Erlang (circa 1997). Andreas Pauley – @apauley Types in Erlang
  7. 7. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Yes and No :-/ The Haskell giants Simon Marlow and Philip Wadler spent over a year developing a static type system for Erlang (circa 1997). Only a subset of the language could be type-checked. Andreas Pauley – @apauley Types in Erlang
  8. 8. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Yes and No :-/ The Haskell giants Simon Marlow and Philip Wadler spent over a year developing a static type system for Erlang (circa 1997). Only a subset of the language could be type-checked. Process types and inter-process messages could not be type-checked. Andreas Pauley – @apauley Types in Erlang
  9. 9. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  10. 10. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Declaring Types We can declare union/sum types and product types: -type suit() :: spades | clubs | hearts | diamonds. -type value() :: 1..10 | jack | queen | king. -type card() :: {suit(), value()}. Andreas Pauley – @apauley Types in Erlang
  11. 11. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Declaring Types Types in record definitions: -record(rsa_id_number, {birth_date gender_digit sequence_nr citizen_digit digit_a checksum_digit Andreas Pauley – @apauley Types in Erlang :: :: :: :: :: :: calendar:date(), 0..9, 0..999, 0 | 1, 0..9, 0..9}).
  12. 12. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Using Types -spec suit(card()) -> suit(). suit({Suit, _}) -> Suit. Andreas Pauley – @apauley Types in Erlang
  13. 13. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Using Types -type gender() :: male | female. -type rsa_id_number() :: #rsa_id_number{}. -export_type([rsa_id_number/0]). -spec gender(rsa_id_number()) -> gender(). gender(#rsa_id_number{gender_digit=GenderDigit}) when GenderDigit >= 5 -> male; gender(#rsa_id_number{gender_digit=GenderDigit}) when GenderDigit < 5 -> female. Andreas Pauley – @apauley Types in Erlang
  14. 14. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  15. 15. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A static analysis tool developed by Kostis Sagonas from the University of Uppsala in Sweden. Andreas Pauley – @apauley Types in Erlang
  16. 16. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A static analysis tool developed by Kostis Sagonas from the University of Uppsala in Sweden. Type inference based on Success Typing instead of Hindley-Milner. Andreas Pauley – @apauley Types in Erlang
  17. 17. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A static analysis tool developed by Kostis Sagonas from the University of Uppsala in Sweden. Type inference based on Success Typing instead of Hindley-Milner. Doesn’t need type specifications, but you get more useful results if you provide them. Andreas Pauley – @apauley Types in Erlang
  18. 18. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Dialyzer and Types -type suit() :: spades | clubs | hearts | diamonds. -type value() :: 1..10 | jack | queen | king. -type card() :: {suit(), value()}. Andreas Pauley – @apauley Types in Erlang
  19. 19. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Dialyzer and Types -spec kind(card()) -> face | number. kind({_, A}) when A >= 1, A =< 10 -> number; kind(_) -> face. main() -> number face number face = = = = kind({spades, 7}), kind({hearts, king}), kind({rubies, 4}), kind({clubs, queen}). Andreas Pauley – @apauley Types in Erlang
  20. 20. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Dialyzer and Types Checking whether the PLT .deps_plt is up-to-date... yes Proceeding with analysis... src/cards.erl:15: Function main/0 has no local return src/cards.erl:18: The call cards:kind({’rubies’,4}) breaks the contract (card()) -> ’face’ | ’number’ done in 0m0.54s done (warnings were emitted) make: *** [dialyzer] Error 2 Andreas Pauley – @apauley Types in Erlang
  21. 21. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  22. 22. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A QuickCheck-inspired property-based testing tool for Erlang. Andreas Pauley – @apauley Types in Erlang
  23. 23. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A QuickCheck-inspired property-based testing tool for Erlang. Developed by Manolis Papadakis, Eirini Arvaniti and Kostis Sagonas from the National Technical University of Athens. Andreas Pauley – @apauley Types in Erlang
  24. 24. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Discrepency Analyzer for Erlang A QuickCheck-inspired property-based testing tool for Erlang. Developed by Manolis Papadakis, Eirini Arvaniti and Kostis Sagonas from the National Technical University of Athens. Has the ability to generate random tests based on type specs. Andreas Pauley – @apauley Types in Erlang
  25. 25. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Property tests from the specs 2> proper:check_specs(rsa_id_number). Testing rsa_id_number:checksum/1 ........................................................... OK: Passed 100 test(s). Testing rsa_id_number:citizen/1 ........................................................... OK: Passed 100 test(s). Testing rsa_id_number:gender/1 ........................................................... OK: Passed 100 test(s). Andreas Pauley – @apauley Types in Erlang
  26. 26. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Table of Contents 1 Erlang Type Overview 2 Can we add compile-time types to Erlang? 3 Optional Types 4 Dialyzer 5 Proper 6 Conclusion Andreas Pauley – @apauley Types in Erlang
  27. 27. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Conclusion On its own, type declarations is maybe just a way to comment your code. Andreas Pauley – @apauley Types in Erlang
  28. 28. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Conclusion On its own, type declarations is maybe just a way to comment your code. With the extra tool support and some effort we’re getting a lot of benefit typically only found in statically typed languages. Andreas Pauley – @apauley Types in Erlang
  29. 29. Erlang Type Overview Can we add compile-time types to Erlang? Optional Types Dialyzer Proper Conclusion Conclusion On its own, type declarations is maybe just a way to comment your code. With the extra tool support and some effort we’re getting a lot of benefit typically only found in statically typed languages. It’s far from perfect. Andreas Pauley – @apauley Types in Erlang
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