170 lines
4.6 KiB
Markdown
170 lines
4.6 KiB
Markdown
# Expr
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[](https://travis-ci.org/antonmedv/expr)
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[](https://goreportcard.com/report/github.com/antonmedv/expr)
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[](https://godoc.org/github.com/antonmedv/expr)
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<img src="docs/images/logo-small.png" width="150" alt="expr logo" align="right">
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**Expr** package provides an engine that can compile and evaluate expressions.
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An expression is a one-liner that returns a value (mostly, but not limited to, booleans).
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It is designed for simplicity, speed and safety.
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The purpose of the package is to allow users to use expressions inside configuration for more complex logic.
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It is a perfect candidate for the foundation of a _business rule engine_.
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The idea is to let configure things in a dynamic way without recompile of a program:
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```coffeescript
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# Get the special price if
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user.Group in ["good_customers", "collaborator"]
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# Promote article to the homepage when
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len(article.Comments) > 100 and article.Category not in ["misc"]
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# Send an alert when
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product.Stock < 15
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```
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## Features
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* Seamless integration with Go (no need to redefine types)
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* Static typing ([example](https://godoc.org/github.com/antonmedv/expr#example-Env)).
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```go
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out, err := expr.Compile(`name + age`)
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// err: invalid operation + (mismatched types string and int)
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// | name + age
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// | .....^
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```
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* User-friendly error messages.
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* Reasonable set of basic operators.
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* Builtins `all`, `none`, `any`, `one`, `filter`, `map`.
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```coffeescript
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all(Tweets, {.Size <= 280})
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```
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* Fast ([benchmarks](https://github.com/antonmedv/golang-expression-evaluation-comparison#readme)): uses bytecode virtual machine and optimizing compiler.
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## Install
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```
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go get github.com/antonmedv/expr
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```
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## Documentation
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* See [Getting Started](docs/Getting-Started.md) page for developer documentation.
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* See [Language Definition](docs/Language-Definition.md) page to learn the syntax.
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## Expr Code Editor
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<a href="http://bit.ly/expr-code-editor">
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<img src="https://antonmedv.github.io/expr/ogimage.png" align="center" alt="Expr Code Editor" width="1200">
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</a>
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Also, I have an embeddable code editor written in JavaScript which allows editing expressions with syntax highlighting and autocomplete based on your types declaration.
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[Learn more →](https://antonmedv.github.io/expr/)
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## Examples
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[Play Online](https://play.golang.org/p/z7T8ytJ1T1d)
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```go
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package main
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import (
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"fmt"
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"github.com/antonmedv/expr"
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)
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func main() {
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env := map[string]interface{}{
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"greet": "Hello, %v!",
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"names": []string{"world", "you"},
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"sprintf": fmt.Sprintf,
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}
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code := `sprintf(greet, names[0])`
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program, err := expr.Compile(code, expr.Env(env))
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if err != nil {
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panic(err)
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}
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output, err := expr.Run(program, env)
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if err != nil {
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panic(err)
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}
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fmt.Println(output)
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}
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```
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[Play Online](https://play.golang.org/p/4S4brsIvU4i)
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```go
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package main
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import (
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"fmt"
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"github.com/antonmedv/expr"
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)
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type Tweet struct {
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Len int
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}
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type Env struct {
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Tweets []Tweet
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}
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func main() {
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code := `all(Tweets, {.Len <= 240})`
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program, err := expr.Compile(code, expr.Env(Env{}))
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if err != nil {
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panic(err)
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}
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env := Env{
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Tweets: []Tweet{{42}, {98}, {69}},
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}
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output, err := expr.Run(program, env)
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if err != nil {
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panic(err)
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}
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fmt.Println(output)
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}
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```
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## Contributing
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**Expr** consist of a few packages for parsing source code to AST, type checking AST, compiling to bytecode and VM for running bytecode program.
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Also expr provides powerful tool [exe](cmd/exe) for debugging. It has interactive terminal debugger for our bytecode virtual machine.
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<p align="center">
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<img src="docs/images/debug.gif" alt="debugger" width="605">
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</p>
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## Who is using Expr?
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<table>
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<tr>
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<td>
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<p align="center"><a href="https://aviasales.ru"><img alt="Aviasales Logo" height="100" src="https://cdn.worldvectorlogo.com/logos/aviasales-4.svg"></a></p>
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<p><a href="https://aviasales.ru">Aviasales</a> are actively using Expr for different parts of the search engine.</p>
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</td>
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<td>
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<p align="center"><a href="https://www.mysteryminds.com/en/"><img alt="Mystery Minds Logo" height="100" src="https://www.mysteryminds.com/wp-content/uploads/2018/07/MM_logo_colours.png"></a></p>
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<p><a href="https://www.mysteryminds.com/en/">Mystery Minds</a> uses Expr to allow easy yet powerful customization of its matching algorithm.</p>
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</td>
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</tr>
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</table>
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[Add you company too](https://github.com/antonmedv/expr/edit/master/README.md)
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## License
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[MIT](LICENSE)
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