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Expr

test Go Report Card Fuzzing Status GoDoc

Expr is a Go-centric expression language designed to deliver dynamic configurations with unparalleled accuracy, safety, and speed. Expr combines simple syntax with powerful features for ease of use:

// Allow only admins and moderators to moderate comments.
user.Group in ["admin", "moderator"] || user.Id == comment.UserId
// Determine whether the request is in the permitted time window.
request.Time - resource.Age < duration("24h")
// 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.
    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 for more details.

Install

go get github.com/expr-lang/expr

Documentation

Examples

Play Online

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

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 uses Expr as one of its expression languages on the Google Cloud Platform.
  • Uber uses Expr to allow customization of its Uber Eats marketplace.
  • GoDaddy employs Expr for the customization of its GoDaddy Pro product.
  • ByteDance incorporates Expr into its internal business rule engine.
  • Aviasales utilizes Expr as a business rule engine for its flight search engine.
  • Wish.com employs Expr in its decision-making rule engine for the Wish Assistant.
  • Argo integrates Expr into Argo Rollouts and Argo Workflows for Kubernetes.
  • OpenTelemetry integrates Expr into the OpenTelemetry Collector.
  • Philips Labs employs Expr in Tabia, a tool designed to collect insights on their code bases.
  • CrowdSec incorporates Expr into its security automation tool.
  • CoreDNS uses Expr in CoreDNS, which is a DNS server.
  • qiniu implements Expr in its trade systems.
  • Junglee Games uses Expr for its in-house marketing retention tool, Project Audience.
  • Faceit uses Expr to enhance customization of its eSports matchmaking algorithm.
  • Chaos Mesh incorporates Expr into Chaos Mesh, a cloud-native Chaos Engineering platform.
  • Visually.io employs Expr as a business rule engine for its personalization targeting algorithm.
  • Akvorado utilizes Expr to classify exporters and interfaces in network flows.
  • keda.sh uses Expr to allow customization of its Kubernetes-based event-driven autoscaling.

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License

MIT