github.com/google/skylark
Package skylark provides a Skylark interpreter. Skylark values are represented by the Value interface. The following built-in Value types are known to the evaluator: Client applications may define new data types that satisfy at least the Value interface. Such types may provide additional operations by implementing any of these optional interfaces: Client applications may also define domain-specific functions in Go and make them available to Skylark programs. Use NewBuiltin to construct a built-in value that wraps a Go function. The implementation of the Go function may use UnpackArgs to make sense of the positional and keyword arguments provided by the caller. Skylark's None value is not equal to Go's nil, but nil may be assigned to a Skylark Value. Be careful to avoid allowing Go nil values to leak into Skylark data structures. The Compare operation requires two arguments of the same type, but this constraint cannot be expressed in Go's type system. (This is the classic "binary method problem".) So, each Value type's CompareSameType method is a partial function that compares a value only against others of the same type. Use the package's standalone Compare (or Equal) function to compare an arbitrary pair of values. To parse and evaluate a Skylark source file, use ExecFile. The Eval function evaluates a single expression. All evaluator functions require a Thread parameter which defines the "thread-local storage" of a Skylark thread and may be used to plumb application state through Sklyark code and into callbacks. When evaluation fails it returns an EvalError from which the application may obtain a backtrace of active Skylark calls.
Readme
Skylark is now called Starlark. The project has moved to go.starlark.net.
This is the home of the Skylark in Go project. Skylark in Go is an interpreter for Skylark, implemented in Go.
Skylark is a dialect of Python intended for use as a configuration language. Like Python, it is an untyped dynamic language with high-level data types, first-class functions with lexical scope, and garbage collection. Unlike CPython, independent Skylark threads execute in parallel, so Skylark workloads scale well on parallel machines. Skylark is a small and simple language with a familiar and highly readable syntax. You can use it as an expressive notation for structured data, defining functions to eliminate repetition, or you can use it to add scripting capabilities to an existing application.
A Skylark interpreter is typically embedded within a larger application, and the application may define additional domain-specific functions and data types beyond those provided by the core language. For example, Skylark was originally developed for the Bazel build tool. Bazel uses Skylark as the notation both for its BUILD files (like Makefiles, these declare the executables, libraries, and tests in a directory) and for its macro language, through which Bazel is extended with custom logic to support new languages and compilers.
Language definition: doc/spec.md
About the Go implementation: doc/impl.md
API documentation: godoc.org/github.com/google/skylark
Mailing list: skylark-go
Issue tracker: https://github.com/google/skylark/issues
Travis CI: 
https://travis-ci.org/google/skylark
Build the code:
$ go get github.com/google/skylark/...
$ go build github.com/google/skylark/cmd/skylark
Run the interpreter:
$ cat coins.sky
coins = {
'dime': 10,
'nickel': 5,
'penny': 1,
'quarter': 25,
}
print('By name:\t' + ', '.join(sorted(coins.keys())))
print('By value:\t' + ', '.join(sorted(coins.keys(), key=coins.get)))
$ ./skylark coins.sky
By name: dime, nickel, penny, quarter
By value: penny, nickel, dime, quarter
Interact with the read-eval-print loop (REPL):
$ ./skylark
>>> def fibonacci(n):
... res = list(range(n))
... for i in res[2:]:
... res[i] = res[i-2] + res[i-1]
... return res
...
>>> fibonacci(10)
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
>>>
When you have finished, type Ctrl-D to close the REPL's input stream.
We welcome submissions but please let us know what you're working on if you want to change or add to the Skylark repository.
Before undertaking to write something new for the Skylark project, please file an issue or claim an existing issue. All significant changes to the language or to the interpreter's Go API must be discussed before they can be accepted. This gives all participants a chance to validate the design and to avoid duplication of effort.
Despite some differences, the Go implementation of Skylark strives to match the behavior of the Java implementation used by Bazel. For that reason, proposals to change the language itself should generally be directed to the Bazel team, not to the maintainers of this project. Only once there is consensus that a language change is desirable may its Go implementation proceed.
We use GitHub pull requests for contributions.
Please complete Google's contributor license agreement (CLA) before sending your first change to the project. If you are the copyright holder, you will need to agree to the individual contributor license agreement, which can be completed online. If your organization is the copyright holder, the organization will need to agree to the corporate contributor license agreement. If the copyright holder for your contribution has already completed the agreement in connection with another Google open source project, it does not need to be completed again.
We reserve the right to make breaking language and API changes at this stage in the project, although we will endeavor to keep them to a minimum. Now that the project's long-term name ("Starlark") has been decided, we plan to copy this repository to github.com/google/starlark and change the canonical import path for all packages to starlark.net/starlark. The current github.com/google/skylark repository will be frozen. Once the Bazel team has finalized the version 1 language specification, we will be more rigorous with interface stability.
Skylark was designed and implemented in Java by Ulf Adams, Lukács Berki, Jon Brandvein, John Field, Laurent Le Brun, Dmitry Lomov, Damien Martin-Guillerez, Vladimir Moskva, and Florian Weikert, standing on the shoulders of the Python community. The Go implementation was written by Alan Donovan and Jay Conrod; its scanner was derived from one written by Russ Cox.
Skylark in Go is Copyright (c) 2017 The Bazel Authors. All rights reserved.
It is provided under a 3-clause BSD license: LICENSE.
The name "Skylark" is a code name of the Bazel project. The Bazel team plans to rename the language to "Starlark" to reflect its applicability to projects unrelated to Bazel.
Skylark in Go is not an official Google product.
FAQs
Package skylark provides a Skylark interpreter. Skylark values are represented by the Value interface. The following built-in Value types are known to the evaluator: Client applications may define new data types that satisfy at least the Value interface. Such types may provide additional operations by implementing any of these optional interfaces: Client applications may also define domain-specific functions in Go and make them available to Skylark programs. Use NewBuiltin to construct a built-in value that wraps a Go function. The implementation of the Go function may use UnpackArgs to make sense of the positional and keyword arguments provided by the caller. Skylark's None value is not equal to Go's nil, but nil may be assigned to a Skylark Value. Be careful to avoid allowing Go nil values to leak into Skylark data structures. The Compare operation requires two arguments of the same type, but this constraint cannot be expressed in Go's type system. (This is the classic "binary method problem".) So, each Value type's CompareSameType method is a partial function that compares a value only against others of the same type. Use the package's standalone Compare (or Equal) function to compare an arbitrary pair of values. To parse and evaluate a Skylark source file, use ExecFile. The Eval function evaluates a single expression. All evaluator functions require a Thread parameter which defines the "thread-local storage" of a Skylark thread and may be used to plumb application state through Sklyark code and into callbacks. When evaluation fails it returns an EvalError from which the application may obtain a backtrace of active Skylark calls.
Did you know?
Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.
Security News
The June TC39 meeting wrapped up this week with eight proposals moving on to the next stage. Here's a quick roundup of the features that the committee approved to advance.
Security News
Cyber extortion in the US and Canada hit record levels in 2023, with ransomware attacks surging and median ransom demands skyrocketing, though fewer companies are choosing to pay ransoms.
Security News
Ecma TC39 is meeting this week and has moved key ECMAScript proposals forward, advancing Deferred Import Evaluation, Error.isError(), RegExp Escaping, and Promise.try to the next stages.