Presentation - DSLs in Kotlin by Niranjan Ratnakar

Presentation slides for SD Kotlin's July 2018 meeting

Transcript

1. Domain Specific Languages
   (DSLs) in Kotlin
   Niranjan Ratnakar
   

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2. Outline
   ●
   What are DSLs?
   ●
   Why should we use DSLs?
   ●
   Kotlin features to enable DSLs
   ●
   Walk through of type safe HTML builder
   

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3. What are DSLs?
   ●
   [Wikipedia definition]
   ●
   A domain-specific language (DSL) is a
   computer language specialized to a particular
   application domain.
   ●
   This is in contrast to a general-purpose
   language (GPL), which is broadly applicable
   across domains.
   

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4. What are DSLs?
   ●
   A DSL is like an electric drill: it is a powerful
   tool with a wide variety of uses, but a specific
   context, namely, putting holes in things.
   ●
   A GPL is a complete workbench, with a variety
   of tools intended for performing a variety of
   tasks.
   

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5. Another example of DSLs
   ●
   Recently, companies are working on AI
   processors
   ●
   AI can be done by CPUs and GPUs
   ●
   Why do we need custom AI processors?
   – Power efficiency
   – Speed
   

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6. Examples
   ●
   Regular expressions
   ●
   SQL
   ●
   Android layouts (?)
   – Implemented traditionally in XML
   – Inflated by Android framework at runtime
   

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7. Why use DSLs?
   ●
   Code looks closer to domain description. It is at
   a higher level of abstraction.
   ●
   Lesser cognitive load for domain experts to
   write and maintain code.
   ●
   The compiler (if applicable) can provide
   assistance while writing code.
   – We will see this in the type safe builder
   example
   

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8. Why use DSL? (Advanced)
   ●
   We wont go into much details on this topic.
   ●
   Interpreter design pattern
   – Write a program description using a
   restricted set of primitives
   – Interpret the program separately
   ●
   Multiple interpretations for a single program
   ●
   Example, evaluate an expression tree or print it
   

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9. Kotlin support for DSLs
   ●
   Write DSLs with Kotlin as the host language
   ●
   Programs look closer to the domain
   ●
   Can use language constructs
   – for, if, ...
   ●
   Example, Anko for android layouts
   – Better looking layout
   – Easier data binding
   

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10. Anko
    

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11. Kotlin features to enable DSLs
    ●
    Extension functions
    –
    http://kotlinlang.org/docs/reference/extensions.html
    ●
    Lambda with receivers
    –
    http://kotlinlang.org/docs/reference/lambdas.html
    ●
    Passing a lambda to the last parameter
    –
    https://kotlinlang.org/docs/reference/lambdas.html
    

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16. Type safe HTML builders
    ●
    http://kotlinlang.org/docs/reference/type-safe-
    builders.html
    ●
    https://try.kotlinlang.org/#/Examples/Longer
    %20examples/HTML%20Builder/HTML
    %20Builder.kt
    ●
    

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17. Walkthrough
    ●
    Specify the HTML document as a DSL
    – (Work with a subset of HTML tags)
    – Can have tags that depend on command
    line arguments
    ●
    Covert the HTML document to a string
    ●
    Use StringBuilder for efficiency
    ●
    Lets go to code!
    

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