Expression Language for Go
Expr is a Go-centric expression language designed to deliver dynamic configurations with unparalleled accuracy, safety, and speed.
Expressive and Intuitive
Write complex logic in simple, readable expressions.
Access Control
user.Group in ["admin", "moderator"] || user.Id == comment.UserId
Date Arithmetic
request.Time - resource.Age < duration("24h")
Collection Predicates
all(tweets, len(.Content) <= 240)
Why Expr?
Safe, fast, and intuitive expression evaluation optimized for Go.
Safe Execution
Memory-safe, side-effect-free, and always terminating. No access to unrelated memory or infinite loops.
Go Integration
Seamlessly integrates into Go projects without redefining types. Use your existing structs and maps directly.
Static Typing
Catches type errors at compile time, not runtime. Know your expressions are correct before executing them.
User-Friendly Errors
Clear, precise error messages with position indicators to help debug expressions quickly.
Built-in Functions
Rich set of built-in functions like all, none, any, one, filter, map, and more out of the box.
High Performance
Optimizing compiler with a bytecode virtual machine delivers best-in-class evaluation speed.
Trusted in Production
Used by leading companies and open-source projects worldwide.
Install
Add Expr to your Go project with a single command.
go get github.com/expr-lang/expr