expr

package module
v1.8.3 Latest Latest
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 Go to latest Published: Apr 19, 2020 License: MIT Imports: 10 Imported by: 0

README

Expr

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expr logo

Expr package provides an engine that can compile and evaluate expressions. An expression is a one-liner that returns a value (mostly, but not limited to, booleans). It is designed for simplicity, speed and safety.

The purpose of the package is to allow users to use expressions inside configuration for more complex logic. It is a perfect candidate for the foundation of a business rule engine. The idea is to let configure things in a dynamic way without recompile of a program:

# Get the special price if
user.Group in ["good_customers", "collaborator"]

# Promote article to the homepage when
len(article.Comments) > 100 and article.Category not in ["misc"]

# Send an alert when
product.Stock < 15

Features

  • Seamless integration with Go (no need to redefine types)
  • Static typing (example). 
    out, err := expr.Compile(`name + age`)
// err: invalid operation + (mismatched types string and int)
// | name + age
// | .....^
  • User-friendly error messages.
  • Reasonable set of basic operators.
  • Builtins all, none, any, one, filter, map. 
    all(Tweets, {.Size <= 280})
  • Fast (benchmarks): uses bytecode virtual machine and optimizing compiler.

Install

go get github.com/antonmedv/expr

Documentation

Expr Code Editor

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)
}

Contributing

Expr consist of a few packages for parsing source code to AST, type checking AST, compiling to bytecode and VM for running bytecode program.

Also expr provides powerful tool exe for debugging. It has interactive terminal debugger for our bytecode virtual machine.

debugger

Who is using Expr?

Aviasales Logo

Aviasales are actively using Expr for different parts of the search engine.

Mystery Minds Logo

Mystery Minds uses Expr to allow easy yet powerful customization of its matching algorithm.

Add you company too

License

MIT

Documentation

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func Compile added in v1.2.0 

func Compile(input string, ops ...Option) (*vm.Program, error)

Compile parses and compiles given input expression to bytecode program.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	env := map[string]interface{}{
		"foo": 1,
		"bar": 99,
	}

	program, err := expr.Compile("foo in 1..99 and bar in 1..99", expr.Env(env))
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output)

}

Output:

true

func Eval 

func Eval(input string, env interface{}) (interface{}, error)

Eval parses, compiles and runs given input.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	output, err := expr.Eval("greet + name", map[string]interface{}{
		"greet": "Hello, ",
		"name":  "world!",
	})
	if err != nil {
		fmt.Printf("err: %v", err)
		return
	}

	fmt.Printf("%v", output)

}

Output:

Hello, world!
Example (Runtime_error) 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	_, err := expr.Eval(`map(1..3, {1 / (# - 3)})`, nil)
	fmt.Print(err)

}

Output:

runtime error: integer divide by zero (1:14)
 | map(1..3, {1 / (# - 3)})
 | .............^

func Run 

func Run(program *vm.Program, env interface{}) (interface{}, error)

Run evaluates given bytecode program.

Types

type Option added in v1.3.1 

type Option func(c *conf.Config)

Option for configuring config.

func AllowUndefinedVariables added in v1.4.0 

func AllowUndefinedVariables() Option

AllowUndefinedVariables allows to use undefined variables inside expressions. This can be used with expr.Env option to partially define a few variables. Note what this option is only works in map environment are used, otherwise runtime.fetch will panic as there is no way to get missing field zero value.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	code := `name == nil ? "Hello, world!" : sprintf("Hello, %v!", name)`

	env := map[string]interface{}{
		"sprintf": fmt.Sprintf,
	}

	options := []expr.Option{
		expr.Env(env),
		expr.AllowUndefinedVariables(), // Allow to use undefined variables.
	}

	program, err := expr.Compile(code, options...)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}
	fmt.Printf("%v\n", output)

	env["name"] = "you" // Define variables later on.

	output, err = expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}
	fmt.Printf("%v\n", output)

}

Output:

Hello, world!
Hello, you!
Example (Zero_value) 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	code := `name == "" ? foo + bar : foo + name`

	// If environment has different zero values, then undefined variables
	// will have it as default value.
	env := map[string]string{}

	options := []expr.Option{
		expr.Env(env),
		expr.AllowUndefinedVariables(), // Allow to use undefined variables.
	}

	program, err := expr.Compile(code, options...)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	env = map[string]string{
		"foo": "Hello, ",
		"bar": "world!",
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}
	fmt.Printf("%v", output)

}

Output:

Hello, world!
Example (Zero_value_functions) 
package main

import (
	"fmt"
	"strings"

	"github.com/antonmedv/expr"
)

func main() {
	code := `words == "" ? Split("foo,bar", ",") : Split(words, ",")`

	// Env is map[string]string type on which methods are defined.
	env := mockMapStringStringEnv{}

	options := []expr.Option{
		expr.Env(env),
		expr.AllowUndefinedVariables(), // Allow to use undefined variables.
	}

	program, err := expr.Compile(code, options...)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}
	fmt.Printf("%v", output)

}

type mockMapStringStringEnv map[string]string

func (m mockMapStringStringEnv) Split(s, sep string) []string {
	return strings.Split(s, sep)
}

Output:

[foo bar]

func AsBool added in v1.2.0 

func AsBool() Option

AsBool tells the compiler to expect boolean result.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	env := map[string]int{
		"foo": 0,
	}

	program, err := expr.Compile("foo >= 0", expr.Env(env), expr.AsBool())
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output.(bool))

}

Output:

true
Example (Error) 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	env := map[string]interface{}{
		"foo": 0,
	}

	_, err := expr.Compile("foo + 42", expr.Env(env), expr.AsBool())

	fmt.Printf("%v", err)

}

Output:

expected bool, but got int

func AsFloat64 added in v1.2.0 

func AsFloat64() Option

AsFloat64 tells the compiler to expect float64 result.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	program, err := expr.Compile("42", expr.AsFloat64())
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, nil)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output.(float64))

}

Output:

42
Example (Error) 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	_, err := expr.Compile(`!!true`, expr.AsFloat64())

	fmt.Printf("%v", err)

}

Output:

expected float64, but got bool

func AsInt64 added in v1.2.0 

func AsInt64() Option

AsInt64 tells the compiler to expect int64 result.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	env := map[string]interface{}{
		"rating": 5.5,
	}

	program, err := expr.Compile("rating", expr.Env(env), expr.AsInt64())
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output.(int64))

}

Output:

5

func ConstExpr added in v1.6.0 

func ConstExpr(fn string) Option

ConstExpr defines func expression as constant. If all argument to this function is constants, then it can be replaced by result of this func call on compile step.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func fib(n int) int {
	if n <= 1 {
		return n
	}
	return fib(n-1) + fib(n-2)
}

func main() {
	code := `[fib(5), fib(3+3), fib(dyn)]`

	env := map[string]interface{}{
		"fib": fib,
		"dyn": 0,
	}

	options := []expr.Option{
		expr.Env(env),
		expr.ConstExpr("fib"), // Mark fib func as constant expression.
	}

	program, err := expr.Compile(code, options...)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	// Only fib(5) and fib(6) calculated on Compile, fib(dyn) can be called at runtime.
	env["dyn"] = 7

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v\n", output)

}

Output:

[5 8 13]

func Env added in v1.0.7 

func Env(env interface{}) Option

Env specifies expected input of env for type checks. If struct is passed, all fields will be treated as variables, as well as all fields of embedded structs and struct itself. If map is passed, all items will be treated as variables. Methods defined on this type will be available as functions.

Example 
package main

import (
	"fmt"

	"github.com/antonmedv/expr"
)

func main() {
	type Segment struct {
		Origin string
	}
	type Passengers struct {
		Adults int
	}
	type Meta struct {
		Tags map[string]string
	}
	type Env struct {
		Meta
		Segments   []*Segment
		Passengers *Passengers
		Marker     string
	}

	code := `all(Segments, {.Origin == "MOW"}) && Passengers.Adults > 0 && Tags["foo"] startsWith "bar"`

	program, err := expr.Compile(code, expr.Env(Env{}))
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	env := Env{
		Meta: Meta{
			Tags: map[string]string{
				"foo": "bar",
			},
		},
		Segments: []*Segment{
			{Origin: "MOW"},
		},
		Passengers: &Passengers{
			Adults: 2,
		},
		Marker: "test",
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output)

}

Output:

true

func Operator added in v1.2.0 

func Operator(operator string, fn ...string) Option

Operator allows to override binary operator with function.

Example 
package main

import (
	"fmt"
	"time"

	"github.com/antonmedv/expr"
)

func main() {
	code := `
		Now() > CreatedAt &&
		(Now() - CreatedAt).Hours() > 24
	`

	type Env struct {
		CreatedAt time.Time
		Now       func() time.Time
		Sub       func(a, b time.Time) time.Duration
		After     func(a, b time.Time) bool
	}

	options := []expr.Option{
		expr.Env(Env{}),
		expr.Operator(">", "After"),
		expr.Operator("-", "Sub"),
	}

	program, err := expr.Compile(code, options...)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	env := Env{
		CreatedAt: time.Date(2018, 7, 14, 0, 0, 0, 0, time.UTC),
		Now:       func() time.Time { return time.Now() },
		Sub:       func(a, b time.Time) time.Duration { return a.Sub(b) },
		After:     func(a, b time.Time) bool { return a.After(b) },
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	fmt.Printf("%v", output)

}

Output:

true

func Optimize added in v1.2.0 

func Optimize(b bool) Option

Optimize turns optimizations on or off.

func Patch added in v1.7.0 

func Patch(visitor ast.Visitor) Option

Patch adds visitor to list of visitors what will be applied before compiling AST to bytecode.

Example 
package main

import (
	"fmt"
	"github.com/antonmedv/expr/ast"

	"github.com/antonmedv/expr"
)

func main() {
	/*
		type patcher struct{}

		func (p *patcher) Enter(_ *ast.Node) {}
		func (p *patcher) Exit(node *ast.Node) {
			switch n := (*node).(type) {
			case *ast.PropertyNode:
				ast.Patch(node, &ast.FunctionNode{
					Name:      "get",
					Arguments: []ast.Node{n.Node, &ast.StringNode{Value: n.Property}},
				})
			}
		}
	*/

	program, err := expr.Compile(
		`greet.you.world + "!"`,
		expr.Patch(&patcher{}),
	)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}

	env := map[string]interface{}{
		"greet": "Hello",
		"get": func(a, b string) string {
			return a + ", " + b
		},
	}

	output, err := expr.Run(program, env)
	if err != nil {
		fmt.Printf("%v", err)
		return
	}
	fmt.Printf("%v", output)

	// Output : Hello, you, world!
}

type patcher struct{}

func (p *patcher) Enter(_ *ast.Node) {}
func (p *patcher) Exit(node *ast.Node) {
	switch n := (*node).(type) {
	case *ast.PropertyNode:
		ast.Patch(node, &ast.FunctionNode{
			Name:      "get",
			Arguments: []ast.Node{n.Node, &ast.StringNode{Value: n.Property}},
		})
	}
}

Output:

Source Files

View all Source files

Directories

Path Synopsis
cmd
exe
debug module
lexer
repl module
vm
generate

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