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).
[](https://github.com/expr-lang/expr/actions/workflows/test.yml)
[](https://goreportcard.com/report/github.com/expr-lang/expr)
[](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:expr)
[](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 its 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 its 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).
* [FastSchema](https://github.com/fastschema/fastschema) - A BaaS leveraging Expr for its customizable and dynamic Access Control system.
* [WunderGraph Cosmo](https://github.com/wundergraph/cosmo) - GraphQL Federeration Router uses Expr to customize Middleware behaviour
* [SOLO](https://solo.one) uses Expr interally to allow dynamic code execution with custom defined functions.
[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)
