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Showing content from https://github.com/expr-lang/expr below:

expr-lang/expr: Expression language and expression evaluation for Go

Expr

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)

Expr is a safe, fast, and intuitive expression evaluator optimized for the Go language. Here are its standout features:

go get github.com/expr-lang/expr

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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)
}

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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)
}

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