monty

README

Monty

Monty is a dialect of Python, supplemented with the Go standard library. Calls into compiled library functions leverage that highly tuned and well tested code. Monty provides a subset of Python. The Monty interpreter is pure Go, calls compiled Go by reflection, and runs without any CGO dependencies.

It is licensed under a 3-clause BSD style license.

Monty is a fork of the starlark-go project. That code is available at https://go.starlark.net , also known as https://github.com/google/starlark-go.

Monty does not aim to be a fully backwards compatible dialect with its predecessors. It is still intuitive and quickly learned. The language definition and implementation documents for Starlark below are still largely accurate.

Major additions:

[x] A package type.
[x] Most Go standard library packages are included.
[x] The `cmd/mk_shadow_lib` utility to bind additional Go libraries (requires re-build).
[x] increment with `++`
[x] decrement with `--`
[x] assignment with `:=` is the same as `=`.
[x] Preliminary complex128 number support. The `cmplx` package is available.
[x] The REPL can handle multiline strings such as docstrings. Link:

https://github.com/google/starlark-go/issues/81

[x] string(raw) will coerce raw []byte to a string; useful in
      `fmt.Printf("%s\n", string(exec.Command("ls", "-al").CombinedOutput())[0])`, for example.
      Try the above at the monty prompt. It works:

$ monty
Welcome to Monty (https://github.com/glycerine/monty), a dialect of Python.
>>> fmt.Printf("%s\n", string(exec.Command("ls", "-al").CombinedOutput())[0])
total 40
drwxr-xr-x   20 mysel  staff   640 Dec 26 20:40 .
drwxrwxr-x  198 mysel  staff  6336 Dec 25 15:27 ..
drwxr-xr-x   13 mysel  staff   416 Dec 26 20:37 .git
-rw-r--r--    1 mysel  staff    89 Dec 25 15:27 .travis.yml
-rw-r--r--    1 mysel  staff  1589 Dec 25 16:01 LICENSE
-rw-r--r--    1 mysel  staff    42 Dec 25 15:58 Makefile
-rw-r--r--    1 mysel  staff  5165 Dec 26 20:40 README.md
drwxr-xr-x    4 mysel  staff   128 Dec 25 18:15 cmd
drwxr-xr-x    4 mysel  staff   128 Dec 25 15:27 doc
drwxr-xr-x   12 mysel  staff   384 Dec 25 15:47 docs
drwxr-xr-x    4 mysel  staff   128 Dec 25 15:27 internal
drwxr-xr-x   25 mysel  staff   800 Dec 25 18:04 lib
drwxr-xr-x    5 mysel  staff   160 Dec 26 20:05 repl
drwxr-xr-x    5 mysel  staff   160 Dec 26 18:20 resolve
drwxr-xr-x   16 mysel  staff   512 Dec 26 19:49 starlark
drwxr-xr-x    5 mysel  staff   160 Dec 26 20:12 starlarkstruct
drwxr-xr-x    4 mysel  staff   128 Dec 26 19:12 starlarktest
drwxr-xr-x   12 mysel  staff   384 Dec 26 17:28 syntax
drwxr-xr-x    3 mysel  staff    96 Dec 25 15:34 vendor
drwxr-xr-x    3 mysel  staff    96 Dec 25 17:12 verb

1114
>>> html  # display contents of standard library html package
package html{EscapeString: <built-in function fn>, UnescapeString: <built-in function fn>}
>>>
>>> # ctrl-D to exit
$

Monty uses reflection code from Nate Finch's https://github.com/starlight-go/starlight project, which is licensed under the MIT license.

All optional features from Starlark-Go are enabled.

This talk by Alan Donovan, https://www.youtube.com/watch?v=9P_YKVhncWI, is a good introduction to the original motivation for Starlark as a configuration language for the Bazel build system.

An adaptation of the README for Starlark-Go follows.

Starlark in Go

Starlark in Go is an interpreter for Starlark, implemented in Go. Starlark was formerly known as Skylark.

Starlark 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 Starlark threads execute in parallel, so Starlark workloads scale well on parallel machines. Starlark 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 Starlark 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, Starlark was originally developed for the Bazel build tool. Bazel uses Starlark 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.

Documentation

• Language definition: doc/spec.md

• About the Go implementation: doc/impl.md

• API documentation: godoc.org/github.com/glycerine/monty/starlark

• Mailing list: starlark-go

• Issue tracker: https://github.com/google/starlark-go/issues

• Travis CI: https://travis-ci.org/google/starlark-go

Getting started

Build the code:

# check out the code and dependencies,
# and install interpreter in $GOPATH/bin
$ go get -u github.com/glycerine/monty/cmd/monty

Run the interpreter:

$ cat coins.star
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)))

$ monty coins.star
By name:	dime, nickel, penny, quarter
By value:	penny, nickel, dime, quarter

Interact with the read-eval-print loop (REPL):

$ monty
>>> 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.

Credits

Starlark 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.

Legal

Monty is Copyright(c) 2018 Jason E. Aten and the Monty authors. All rights reserved.

Starlark in Go is Copyright (c) 2018 The Bazel Authors. All rights reserved.

It is provided under a 3-clause BSD license: LICENSE.

Starlark in Go is not an official Google product.