72 lines
1.8 KiB
Go
72 lines
1.8 KiB
Go
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/*
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Predicate package used to create interpreted mini languages with Go syntax - mostly to define
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various predicates for configuration, e.g. Latency() > 40 || ErrorRate() > 0.5.
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Here's an example of fully functional predicate language to deal with division remainders:
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// takes number and returns true or false
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type numberPredicate func(v int) bool
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// Converts one number to another
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type numberMapper func(v int) int
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// Function that creates predicate to test if the remainder is 0
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func divisibleBy(divisor int) numberPredicate {
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return func(v int) bool {
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return v%divisor == 0
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}
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}
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// Function - logical operator AND that combines predicates
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func numberAND(a, b numberPredicate) numberPredicate {
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return func(v int) bool {
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return a(v) && b(v)
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}
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}
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p, err := NewParser(Def{
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Operators: Operators{
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AND: numberAND,
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},
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Functions: map[string]interface{}{
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"DivisibleBy": divisibleBy,
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},
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})
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pr, err := p.Parse("DivisibleBy(2) && DivisibleBy(3)")
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if err == nil {
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fmt.Fatalf("Error: %v", err)
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}
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pr.(numberPredicate)(2) // false
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pr.(numberPredicate)(3) // false
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pr.(numberPredicate)(6) // true
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*/
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package predicate
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// Def contains supported operators (e.g. LT, GT) and functions passed in as a map.
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type Def struct {
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Operators Operators
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// Function matching is case sensitive, e.g. Len is different from len
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Functions map[string]interface{}
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}
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// Operators contain functions for equality and logical comparison.
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type Operators struct {
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EQ interface{}
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NEQ interface{}
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LT interface{}
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GT interface{}
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LE interface{}
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GE interface{}
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OR interface{}
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AND interface{}
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}
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// Parser takes the string with expression and calls the operators and functions.
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type Parser interface {
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Parse(string) (interface{}, error)
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}
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