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Presentation - DSLs in Kotlin by Niranjan Ratnakar

Presentation - DSLs in Kotlin by Niranjan Ratnakar

Presentation slides for SD Kotlin's July 2018 meeting

SD Kotlin

July 11, 2018

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  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

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  5. Another example of DSLs

    Recently, companies are working on AI

    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


    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

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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


    Lambda with receivers


    Passing a lambda to the last parameter


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  16. Type safe HTML builders



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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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