Starlark

From HandWiki

Starlark is a lightweight, high-level programming language designed for embedded use in applications. It uses a subset of the Python syntax. By default, the code is deterministic and hermetic.[1]

History

Starlark was released in 2015 as part of Bazel under the name Skylark[2]. This first implementation was written in Java. In 2018, the language was renamed Starlark.[3]

In 2017, a new implementation of Starlark in Go was announced.[4]

In 2021, Meta announced an implementation of Starlark written in Rust,[5] to be used for the Buck build system.[6][7]

Popularity

In addition to the Bazel[8] and Buck build systems, Starlark is used by dozens of projects,[9][10] including Isopod[11], skycfg[12], Uber's Starlark Worker[13], and Tilt.[14]

On GitHub, Starlark is among the top 50 languages based on the developer activity.[15][16]

Syntax

Starlark syntax is a strict subset of Python syntax.[1] Similar to Python syntax, Starlark relies on indentation to delimit blocks, using the off-side rule.

Statements and control flow

Starlark's statements include:[17]

  • The = statement to assign a value to a variable
  • The augmented assignment statements to modify a variable
  • The if statement to execute conditionally a block of code (with else or elif)
  • The for statement to iterate over an iterable object
  • The def statement to define a function
  • The break statement to exit a loop
  • The continue statement to skip the rest of the current iteration and continues with the next
  • The pass statement, serving as a NOP, syntactically needed to create an empty code block
  • The return statement to return a value from a function.
  • The load statement, which replaces Python import, to import a value from another module.[18] Unlike Python, the order of load statements does not affect the semantics of the code.[19]

Unlike Python, Starlark statements don't include: while, try, raise, class, with, del, assert, yield, import, match and case.[20]

Freezing

To ensure thread safety and support parallel computing, Starlark has a feature called freezing. At the end of the evaluation of a module, all values become immutable. This means that the values that can be accessed from multiple threads can no longer be modified, which removes the risk of race conditions.[2][21]

See also

References

  1. ↑ 1.0 1.1 Cite error: Invalid <ref> tag; no text was provided for refs named specification overview
  2. ↑ 2.0 2.1 "A glimpse of the design of Skylark". https://blog.bazel.build/2017/03/21/design-of-skylark.html. 
  3. ↑ "Starlark". https://blog.bazel.build/2018/08/17/starlark.html. 
  4. ↑ Donovan, Alan (18 November 2017). A Go implementation of the Skylark Configuration Language. GothamGo 2017 – via YouTube.
  5. ↑ Mitchell, Neil (2021-04-08). "The Rust Starlark library". https://developers.facebook.com/blog/post/2021/04/08/rust-starlark-library/. 
  6. ↑ "Meta open-sources 'significantly faster' build system". https://www.infoworld.com/article/2338301/meta-open-sources-significantly-faster-build-system.html. 
  7. ↑ "5 Things you didn't know about Buck2". 23 October 2023. https://engineering.fb.com/2023/10/23/developer-tools/5-things-you-didnt-know-about-buck2/. 
  8. ↑ Antoniucci, Javier (2024). Ultimate Monorepo and Bazel for Building Apps at Scale: Level up Your Large-Scale Application Development with Monorepo and Bazel for Enhanced Productivity, Scalability, and Integration (English Edition) (1st ed.). Orange Education PVT Ltd. ISBN 9788197223914. 
  9. ↑ "Starlark Programming Language". https://starlark-lang.org/resources.html#users. 
  10. ↑ Pandey, Mohit (12 December 2024). "Starlark is Basically Python, But Not Really Python, and That's Fine". https://analyticsindiamag.com/developers-corner/starlark-is-basically-python-but-not-really-python-and-thats-fine/. 
  11. ↑ Xu, Charles; Ilyevskiy, Dmitry (2019). "Isopod: An expressive DSL for Kubernetes configuration". Proceedings of the ACM Symposium on Cloud Computing. doi:10.1145/3357223.3365759. https://dl.acm.org/doi/abs/10.1145/3357223.3365759. 
  12. ↑ Norton, Peter (2019). "Other Faces of Python". Login Usenix Mag. 44 (2). https://www.usenix.org/system/files/login/articles/login_summer19_09_norton.pdf. 
  13. ↑ "Open-Sourcing Starlark Worker: Define Cadence Workflows with Starlark". https://www.uber.com/blog/starlark/. 
  14. ↑ Sayfan, Gigi (2019). Hands-on microservices with Kubernetes: build, deploy, and manage scalable microservices on Kubernetes (1st ed.). Packt Publishing. pp. 353. ISBN 9781789809732. 
  15. ↑ "Global Metrics: Programming Languages". GitHub. https://innovationgraph.github.com/global-metrics/programming-languages. 
  16. ↑ "Languish - Programming Language Trends". https://tjpalmer.github.io/languish/. 
  17. ↑ "starlark/spec.md at master · bazelbuild/starlark". https://github.com/bazelbuild/starlark/blob/master/spec.md#statements. 
  18. ↑ "starlark/spec.md at master · bazelbuild/starlark". https://github.com/bazelbuild/starlark/blob/master/spec.md#load-statements. 
  19. ↑ Le Brun, Laurent (December 2024). "A practical introduction to the Starlark language" (in en). https://laurent.le-brun.eu/blog/a-practical-introduction-to-the-starlark-language. 
  20. ↑ "starlark/spec.md at master · bazelbuild/starlark". https://github.com/bazelbuild/starlark/blob/master/spec.md#lexical-elements. 
  21. ↑ "starlark/spec.md at master · bazelbuild/starlark". https://github.com/bazelbuild/starlark/blob/master/spec.md#freezing-a-value. 



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