Writing your own DSL
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This document discusses how to write your own domain-specific language (DSL). It begins by defining what a DSL is - a language designed for a particular domain that allows for more expressive communication within that domain. It then covers the key aspects of writing a DSL, including parsing the DSL into an abstract syntax tree using a parser generator like DSL::Maker, validating the parsed structure follows the rules of the language, and producing output from the validated structure. An example DSL for defining vehicle data is used to demonstrate these concepts. The document concludes by noting that production from a parsed DSL structure is left to the developer and encourages an outside-in, multi-pass approach to transformation.
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![#!/usr/bin/env ruby
require vehicle/dsl
filename = ARGV.shift ||
raise No filename provided.
vehicles = Vehicle::DSL.parse_dsl(
IO.read(filename),
)
# Do something here with vehicles
[
Car[
:make => Accord,
:year => 1990,
:engine => Engine[
:hemi => true,
],
],
Car[
:make => Civic,
:year => 2014,
:engine => nil,
],
]](https://image.slidesharecdn.com/dsl-makercrb2015-08-150818125914-lva1-app6891/85/Writing-your-own-DSL-31-320.jpg)
![#!/usr/bin/env ruby
require vehicle/dsl
filename = ARGV.shift ||
raise No filename provided.
vehicles = Vehicle::DSL.parse_dsl(
IO.read(filename),
)
# Do something here with vehicles
[
. . .
Truck[
:make => F-150,
:year => 1999,
:engine => nil
],
. . .
]](https://image.slidesharecdn.com/dsl-makercrb2015-08-150818125914-lva1-app6891/85/Writing-your-own-DSL-33-320.jpg)
Writing your own DSL
- 1. Writing your own DSL Yes, it is that easy!
- 3. Who am I? Rob Kinyon @rkinyon rob.kinyon@gmail.com Devops lead for many years Developer in Ruby, Python, Perl, JS, and others.
- 4. What is a DSL? Domain-Specific Language
- 5. What is a DSL? Domain-Specific Language Language - A vehicle for communication
- 6. What is a DSL? Domain-Specific Language Language - A vehicle for communication Domain - A restrained set of concepts
- 7. What is a DSL? Domain-Specific Language Language - A vehicle for communication Domain - A restrained set of concepts Specific - Limited to.
- 8. What is a DSL? Domain-Specific Language Language - A vehicle for communication Domain - A restrained set of concepts Specific - Limited to. No, really. :)
- 9. Language and Communication Communicate in one direction Author -> Executor
- 10. Language and Communication Communicate in two directions Author -> Executor Author -> Maintainer
- 11. Language and Communication Communicate in three directions Author -> Executor Author -> Maintainer Specifier -> Author
- 12. Language and Communication Communicate in four directions Author -> Executor Author -> Maintainer Specifier -> Author Author -> Verifier
- 13. Language and Communication Communicate in MANY directions Author -> Executor Author -> Maintainer Specifier -> Author Author -> Verifier Author -> Teammate(s) Developer -> Sysadmin/Devops ->
- 14. Language and Communication Communicate in MANY directions Author -> Executor Author -> Maintainer Specifier -> Author Author -> Verifier Author -> Teammate(s) Developer -> Sysadmin/Devops -> The ONLY computer
- 15. Language and Communication Communicate in MANY directions Author -> Executor Author -> Maintainer Specifier -> Author Author -> Verifier Author -> Teammate(s) Developer -> Sysadmin/Devops -> All humans
- 16. Language and Communication Communicate in MANY directions Author -> Executor Author <-> Maintainer Specifier <-> Author Author <-> Verifier Author <-> Teammate(s) Developer <-> Sysadmin/Devops <-> All human communication is two-way
- 17. Domain-Specific Eskimos supposedly have 50+ words for snow Depends on how you count it Saami has 1000+ words dealing with reindeer snarri - a reindeer with short, branched horns busat - a bull with a single, large testicle
- 18. Domain-specific : Busat Busat - The quality of having appropriately-specific expressiveness for the domain.
- 19. DSLs you already use SQL set manipulation DSL CSS tree-visitor-defining DSL for setting metadata HAML HTML-definition DSL Bash A crappy way of issue shell commands with logic
- 20. Places for a DSL Packaging and orchestration most devops/operations activities Configuration file generation web servers monitoring datastores Configuration value management across environments Anything extremely complicated (such as SQL) Anything repetitive (such as CSS)
- 21. Reasons for a DSL Let the important things shine General-purpose is overly-verbose Bugs hide in boilerplate Non-developers can read and comprehend And maybe even propose changes through PRs?
- 22. Reasons for a DSL DSL is to Ruby as Ruby is to Java
- 23. Writing a DSL Three passes Parsing Validation Production
- 24. Writing a DSL - Parsing DSL::Maker for parsing
- 25. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 26. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 27. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 28. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 29. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 30. Car = Struct.new(:make, :year, :engine) Engine = Struct.new(:hemi) class VehicleDSL < DSL::Maker add_entrypoint(:car, { :make => String, :year => Integer, :engine => generate_dsl({ :hemi => Boolean, }) do Engine.new(hemi) end, }) do |*args| default(:make, args, 0) Car.new(make, model, engine) end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 31. #!/usr/bin/env ruby require vehicle/dsl filename = ARGV.shift || raise No filename provided. vehicles = Vehicle::DSL.parse_dsl( IO.read(filename), ) # Do something here with vehicles [ Car[ :make => Accord, :year => 1990, :engine => Engine[ :hemi => true, ], ], Car[ :make => Civic, :year => 2014, :engine => nil, ], ]
- 32. . . . truck F-150 { year 1999 } . . . . . . Truck = Struct.new(:make, :year, :engine) . . . class VehicleDSL < DSL::Maker . . . add_entrypoint(:truck, { :make => String, :year => Integer, :engine => . . ., }) do |*args| default(:make, args, 0) Truck.new(make, model, nil) end end
- 33. #!/usr/bin/env ruby require vehicle/dsl filename = ARGV.shift || raise No filename provided. vehicles = Vehicle::DSL.parse_dsl( IO.read(filename), ) # Do something here with vehicles [ . . . Truck[ :make => F-150, :year => 1999, :engine => nil ], . . . ]
- 34. Writing a DSL - Validation DSL::Maker for parsing DSL::Maker for validation
- 35. . . . class VehicleDSL < DSL::Maker . . . add_validation(:car) do |car| unless car.engine return Cars must have an engine end end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 36. . . . class VehicleDSL < DSL::Maker . . . add_validation(:car) do |car| unless car.engine return Cars must have an engine end end end car { make Accord year 1990 engine { hemi Yes } } car Civic { year 2014 }
- 37. #!/usr/bin/env ruby require vehicle/dsl filename = ARGV.shift || raise No filename provided. # This raises the error vehicles = Vehicle::DSL.parse_dsl( IO.read(filename), ) # Do something here with vehicles Error: Cars must have an engine
- 38. Writing a DSL - Production DSL::Maker for parsing DSL::Maker for validation Youre on your own for production
- 39. Writing a DSL - Production Work from outside in. Parsing is done inside-out. Transform in a series of passes. Expand everything (its just data) Dont do anything irrevocable until the end Work in temp directories, stage everything
- 40. Conclusion DSL::Maker 0.1.0 is available right now Patches welcome 100% test coverage Im blogging about this at http: //streamlined-book.blogspot.com First post on the topic
- 41. Questions?