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
}
