README.md

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:

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
}