Expr

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

// Allow only admins and moderators to moderate comments.
user.Group in ["admin", "moderator"] || user.Id == comment.UserId

// Ensure all tweets are less than 240 characters.
all(Tweets, .Size <= 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/antonmedv/expr

Documentation

See Getting Started page for developer documentation.
See Language Definition page to learn the syntax.

Expr Code Editor

Also, I have an embeddable code editor written in JavaScript which allows editing expressions with syntax highlighting and autocomplete based on your types declaration.

Learn more →

Examples

Play Online

package main

import (
	"fmt"
	"github.com/antonmedv/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/antonmedv/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.
Crowdsec incorporates Expr into its security automation tool.
FACEIT uses Expr to enhance customization of its eSports matchmaking algorithm.
qiniu implements Expr in its trade systems.
Junglee Games uses Expr for its in-house marketing retention tool, Project Audience.
OpenTelemetry integrates Expr into the OpenTelemetry Collector.
Philips Labs employs Expr in Tabia, a tool designed to collect insights on their code bases.
CoreDNS uses Expr in CoreDNS, which is a DNS server.
Chaos Mesh incorporates Expr into Chaos Mesh, a cloud-native Chaos Engineering platform.
Milvus integrates Expr into Milvus, an open-source vector database.
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.