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https://github.com/expr-lang/expr

Expression language and expression evaluation for Go
https://github.com/expr-lang/expr

bytecode configuration-language engine evaluator expr expression expression-evaluator expression-language go golang rule-engine

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Expression language and expression evaluation for Go

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Zx logo Expr



> [!IMPORTANT]

> The repository [github.com/antonmedv/expr](https://github.com/antonmedv/expr) moved to [github.com/**expr-lang**/expr](https://github.com/expr-lang/expr).



[![test](https://github.com/expr-lang/expr/actions/workflows/test.yml/badge.svg)](https://github.com/expr-lang/expr/actions/workflows/test.yml) 

[![Go Report Card](https://goreportcard.com/badge/github.com/expr-lang/expr)](https://goreportcard.com/report/github.com/expr-lang/expr) 

[![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/expr.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:expr)

[![GoDoc](https://godoc.org/github.com/expr-lang/expr?status.svg)](https://godoc.org/github.com/expr-lang/expr)



**Expr** is a Go-centric expression language designed to deliver dynamic configurations with unparalleled accuracy, safety, and speed. 

**Expr** combines simple [syntax](https://expr-lang.org/docs/language-definition) with powerful features for ease of use:



```js

// Allow only admins and moderators to moderate comments.

user.Group in ["admin", "moderator"] || user.Id == comment.UserId

```



```js

// Determine whether the request is in the permitted time window.

request.Time - resource.Age < duration("24h")

```



```js

// Ensure all tweets are less than 240 characters.

all(tweets, len(.Content) <= 240)

```



## Features



**Expr** is a safe, fast, and intuitive expression evaluator optimized for the Go language. 

Here are its standout features:



### Safety and Isolation

* **Memory-Safe**: Expr is designed with a focus on safety, ensuring that programs do not access unrelated memory or introduce memory vulnerabilities.

* **Side-Effect-Free**: Expressions evaluated in Expr only compute outputs from their inputs, ensuring no side-effects that can change state or produce unintended results.

* **Always Terminating**: Expr is designed to prevent infinite loops, ensuring that every program will conclude in a reasonable amount of time.



### Go Integration

* **Seamless with Go**: Integrate Expr into your Go projects without the need to redefine types.



### Static Typing

* Ensures type correctness and prevents runtime type errors.

  ```go

  out, err := expr.Compile(`name + age`)

  // err: invalid operation + (mismatched types string and int)

  // | name + age

  // | .....^

  ```



### User-Friendly

* Provides user-friendly error messages to assist with debugging and development.



### Flexibility and Utility

* **Rich Operators**: Offers a reasonable set of basic operators for a variety of applications.

* **Built-in Functions**: Functions like `all`, `none`, `any`, `one`, `filter`, and `map` are provided out-of-the-box.



### Performance

* **Optimized for Speed**: Expr stands out in its performance, utilizing an optimizing compiler and a bytecode virtual machine. Check out these [benchmarks](https://github.com/antonmedv/golang-expression-evaluation-comparison#readme) for more details.



## Install



```

go get github.com/expr-lang/expr

```



## Documentation



* See [Getting Started](https://expr-lang.org/docs/Getting-Started) page for developer documentation.

* See [Language Definition](https://expr-lang.org/docs/language-definition) page to learn the syntax.



## Examples



[Play Online](https://go.dev/play/p/XCoNXEjm3TS)



```go

package main



import (

	"fmt"

	"github.com/expr-lang/expr"

)



func main() {

	env := map[string]interface{}{

		"greet":   "Hello, %v!",

		"names":   []string{"world", "you"},

		"sprintf": fmt.Sprintf,

	}



	code := `sprintf(greet, names[0])`



	program, err := expr.Compile(code, expr.Env(env))

	if err != nil {

		panic(err)

	}



	output, err := expr.Run(program, env)

	if err != nil {

		panic(err)

	}



	fmt.Println(output)

}

```



[Play Online](https://go.dev/play/p/tz-ZneBfSuw)



```go

package main



import (

	"fmt"

	"github.com/expr-lang/expr"

)



type Tweet struct {

	Len int

}



type Env struct {

	Tweets []Tweet

}



func main() {

	code := `all(Tweets, {.Len <= 240})`



	program, err := expr.Compile(code, expr.Env(Env{}))

	if err != nil {

		panic(err)

	}



	env := Env{

		Tweets: []Tweet{{42}, {98}, {69}},

	}

	output, err := expr.Run(program, env)

	if err != nil {

		panic(err)

	}



	fmt.Println(output)

}

```



## Who uses Expr?



* [Google](https://google.com) uses Expr as one of its expression languages on the [Google Cloud Platform](https://cloud.google.com).

* [Uber](https://uber.com) uses Expr to allow customization of its Uber Eats marketplace.

* [GoDaddy](https://godaddy.com) employs Expr for the customization of its GoDaddy Pro product.

* [ByteDance](https://bytedance.com) incorporates Expr into its internal business rule engine.

* [Aviasales](https://aviasales.ru) utilizes Expr as a business rule engine for its flight search engine.

* [Wish.com](https://www.wish.com) employs Expr in its decision-making rule engine for the Wish Assistant.

* [Argo](https://argoproj.github.io) integrates Expr into Argo Rollouts and Argo Workflows for Kubernetes.

* [OpenTelemetry](https://opentelemetry.io) integrates Expr into the OpenTelemetry Collector.

* [Philips Labs](https://github.com/philips-labs/tabia) employs Expr in Tabia, a tool designed to collect insights on their code bases.

* [CrowdSec](https://crowdsec.net) incorporates Expr into its security automation tool.

* [CoreDNS](https://coredns.io) uses Expr in CoreDNS, which is a DNS server.

* [qiniu](https://www.qiniu.com) implements Expr in its trade systems.

* [Junglee Games](https://www.jungleegames.com/) uses Expr for its in-house marketing retention tool, Project Audience.

* [Faceit](https://www.faceit.com) uses Expr to enhance customization of its eSports matchmaking algorithm.

* [Chaos Mesh](https://chaos-mesh.org) incorporates Expr into Chaos Mesh, a cloud-native Chaos Engineering platform.

* [Visually.io](https://visually.io) employs Expr as a business rule engine for its personalization targeting algorithm.

* [Akvorado](https://github.com/akvorado/akvorado) utilizes Expr to classify exporters and interfaces in network flows.

* [keda.sh](https://keda.sh) uses Expr to allow customization of its Kubernetes-based event-driven autoscaling.

* [Span Digital](https://spandigital.com/) uses Expr in it's Knowledge Management products.

* [Xiaohongshu](https://www.xiaohongshu.com/) combining yaml with Expr for dynamically policies delivery.

* [Melrōse](https://melrōse.org) uses Expr to implement its music programming language.

* [Tork](https://www.tork.run/) integrates Expr into its workflow execution.

* [Critical Moments](https://criticalmoments.io) uses Expr for it's mobile realtime conditional targeting system.

* [WoodpeckerCI](https://woodpecker-ci.org) uses Expr for [filtering workflows/steps](https://woodpecker-ci.org/docs/usage/workflow-syntax#evaluate).



[Add your company too](https://github.com/expr-lang/expr/edit/master/README.md)



## License



[MIT](https://github.com/expr-lang/expr/blob/master/LICENSE)