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README.md

1
2<!-- This file is the project homepage for go.starlark.net -->
3
4# Starlark in Go
5
6[![Travis CI](https://travis-ci.org/google/starlark-go.svg)](https://travis-ci.org/google/starlark-go)
7[![GoDoc](https://godoc.org/go.starlark.net/starlark?status.svg)](https://godoc.org/go.starlark.net/starlark)
8
9This is the home of the _Starlark in Go_ project.
10Starlark in Go is an interpreter for Starlark, implemented in Go.
11Starlark was formerly known as Skylark.
12The new import path for Go packages is `"go.starlark.net/starlark"`.
13
14Starlark is a dialect of Python intended for use as a configuration language.
15Like Python, it is an untyped dynamic language with high-level data
16types, first-class functions with lexical scope, and garbage collection.
17Unlike CPython, independent Starlark threads execute in parallel, so
18Starlark workloads scale well on parallel machines.
19Starlark is a small and simple language with a familiar and highly
20readable syntax. You can use it as an expressive notation for
21structured data, defining functions to eliminate repetition, or you
22can use it to add scripting capabilities to an existing application.
23
24A Starlark interpreter is typically embedded within a larger
25application, and the application may define additional domain-specific
26functions and data types beyond those provided by the core language.
27For example, Starlark was originally developed for the
28[Bazel build tool](https://bazel.build).
29Bazel uses Starlark as the notation both for its BUILD files (like
30Makefiles, these declare the executables, libraries, and tests in a
31directory) and for [its macro
32language](https://docs.bazel.build/versions/master/skylark/language.html),
33through which Bazel is extended with custom logic to support new
34languages and compilers.
35
36
37## Documentation
38
39* Language definition: [doc/spec.md](doc/spec.md)
40
41* About the Go implementation: [doc/impl.md](doc/impl.md)
42
43* API documentation: [godoc.org/go.starlark.net/starlark](https://godoc.org/go.starlark.net/starlark)
44
45* Mailing list: [starlark-go](https://groups.google.com/forum/#!forum/starlark-go)
46
47* Issue tracker: [https://github.com/google/starlark-go/issues](https://github.com/google/starlark-go/issues)
48
49### Getting started
50
51Build the code:
52
53```shell
54# check out the code and dependencies,
55# and install interpreter in $GOPATH/bin
56$ go get -u go.starlark.net/cmd/starlark
57```
58
59Run the interpreter:
60
61```console
62$ cat coins.star
63coins = {
64  'dime': 10,
65  'nickel': 5,
66  'penny': 1,
67  'quarter': 25,
68}
69print('By name:\t' + ', '.join(sorted(coins.keys())))
70print('By value:\t' + ', '.join(sorted(coins.keys(), key=coins.get)))
71
72$ starlark coins.star
73By name:	dime, nickel, penny, quarter
74By value:	penny, nickel, dime, quarter
75```
76
77Interact with the read-eval-print loop (REPL):
78
79```pycon
80$ starlark
81>>> def fibonacci(n):
82...    res = list(range(n))
83...    for i in res[2:]:
84...        res[i] = res[i-2] + res[i-1]
85...    return res
86...
87>>> fibonacci(10)
88[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
89>>>
90```
91
92When you have finished, type `Ctrl-D` to close the REPL's input stream.
93
94Embed the interpreter in your Go program:
95
96```go
97import "go.starlark.net/starlark"
98
99// Execute Starlark program in a file.
100thread := &starlark.Thread{Name: "my thread"}
101globals, err := starlark.ExecFile(thread, "fibonacci.star", nil, nil)
102if err != nil { ... }
103
104// Retrieve a module global.
105fibonacci := globals["fibonacci"]
106
107// Call Starlark function from Go.
108v, err := starlark.Call(thread, fibonacci, starlark.Tuple{starlark.MakeInt(10)}, nil)
109if err != nil { ... }
110fmt.Printf("fibonacci(10) = %v\n", v) // fibonacci(10) = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
111```
112
113See [starlark/example_test.go](starlark/example_test.go) for more examples.
114
115### Contributing
116
117We welcome submissions but please let us know what you're working on
118if you want to change or add to the Starlark repository.
119
120Before undertaking to write something new for the Starlark project,
121please file an issue or claim an existing issue.
122All significant changes to the language or to the interpreter's Go
123API must be discussed before they can be accepted.
124This gives all participants a chance to validate the design and to
125avoid duplication of effort.
126
127Despite some differences, the Go implementation of Starlark strives to
128match the behavior of [the Java implementation](https://github.com/bazelbuild/bazel)
129used by Bazel and maintained by the Bazel team.
130For that reason, proposals to change the language itself should
131generally be directed to [the Starlark site](
132https://github.com/bazelbuild/starlark/), not to the maintainers of this
133project.
134Only once there is consensus that a language change is desirable may
135its Go implementation proceed.
136
137We use GitHub pull requests for contributions.
138
139Please complete Google's contributor license agreement (CLA) before
140sending your first change to the project.  If you are the copyright
141holder, you will need to agree to the
142[individual contributor license agreement](https://cla.developers.google.com/about/google-individual),
143which can be completed online.
144If your organization is the copyright holder, the organization will
145need to agree to the [corporate contributor license agreement](https://cla.developers.google.com/about/google-corporate).
146If the copyright holder for your contribution has already completed
147the agreement in connection with another Google open source project,
148it does not need to be completed again.
149
150### Stability
151
152We reserve the right to make breaking language and API changes at this
153stage in the project, although we will endeavor to keep them to a minimum.
154Once the Bazel team has finalized the version 1 language specification,
155we will be more rigorous with interface stability.
156
157### Credits
158
159Starlark was designed and implemented in Java by
160Ulf Adams,
161Lukács Berki,
162Jon Brandvein,
163John Field,
164Laurent Le Brun,
165Dmitry Lomov,
166Damien Martin-Guillerez,
167Vladimir Moskva, and
168Florian Weikert,
169standing on the shoulders of the Python community.
170The Go implementation was written by Alan Donovan and Jay Conrod;
171its scanner was derived from one written by Russ Cox.
172
173### Legal
174
175Starlark in Go is Copyright (c) 2018 The Bazel Authors.
176All rights reserved.
177
178It is provided under a 3-clause BSD license:
179[LICENSE](https://github.com/google/starlark-go/blob/master/LICENSE).
180
181Starlark in Go is not an official Google product.
182