https://github.com/vulcand/predicate

Library for creating predicate mini-languages in Go
https://github.com/vulcand/predicate

go golang mini-language predicate

Last synced: 4 days ago
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Library for creating predicate mini-languages in Go

• Host: GitHub
• URL: https://github.com/vulcand/predicate
• Owner: vulcand
• License: apache-2.0
• Created: 2014-10-19T02:29:19.000Z (about 10 years ago)
• Default Branch: master
• Last Pushed: 2024-12-12T00:26:08.000Z (22 days ago)
• Last Synced: 2024-12-23T04:00:38.359Z (11 days ago)
• Topics: go, golang, mini-language, predicate
• Language: Go
• Homepage: https://pkg.go.dev/github.com/vulcand/predicate#section-readme
• Size: 43 KB
• Stars: 96
• Watchers: 23
• Forks: 17
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Predicate

Predicate package used to create interpreted mini languages with Go syntax - mostly to define

various predicates for configuration, e.g. 

```

Latency() > 40 || ErrorRate() > 0.5.

```

Here's an example of fully functional predicate language to deal with division remainders:

```go

package main

import (

  "log"

	

  "github.com/vulcand/predicate"

)

// takes number and returns true or false

type numberPredicate func(v int) bool

// Converts one number to another

type numberMapper func(v int) int

// Function that creates predicate to test if the remainder is 0

func divisibleBy(divisor int) numberPredicate {

     return func(v int) bool {

         return v%divisor == 0

     }

}

// Function - logical operator AND that combines predicates

func numberAND(a, b numberPredicate) numberPredicate {

    return func(v int) bool {

        return a(v) && b(v)

    }

}

func main(){

    // Create a new parser and define the supported operators and methods

    p, err := predicate.NewParser(predicate.Def{

        Operators: predicate.Operators{

           AND: numberAND,

        },

        Functions: map[string]interface{}{

            "DivisibleBy": divisibleBy,

        },

    })

    pr, err := p.Parse("DivisibleBy(2) && DivisibleBy(3)")

    if err != nil {

		log.Fatalf("Error: %v", err)

	}

	fmt.Println(pr.(numberPredicate)(2)) // false

	fmt.Println(pr.(numberPredicate)(3)) // false

	fmt.Println(pr.(numberPredicate)(6)) // true

}

```