bool expression parser and evaluator

supported grammars

• true, false, number (float64 and int64), string, identifier
• compare operations: = > >= < <= !=
• simple math operations: + - * /
• prefix: -, !
• bracket ()
• custom variable, like $car
• custom none-variadic functions, like : takeBus()
• in, like $car in ('bwm','byd')

grammars limits

• function inputs only supported int64, float64, string, bool
• functions must have one or two returns, the first one must be one of: int64, float64, string, bool, if the second one exists, it must be error
• variables support numbers, including all ints and uints, except uint64
• function does not support variadic args
• if identifier exists, then the expression can only be parsed, but cannot be evaluated

builtin functions:

• contains
• endsWith
• startsWith
• length
• toLower
• toUpper
• trim
• concat
• geoWithin2d
• hasIntersection
• timestampBefore
• now // return time.Now() rfc3339 formatted string

examples

simple one

func ExampleEvaluate() {
	expr := `$car in ('bwm', 'byd') and (3 + 2) * 2.0 = 10 and startsWith($car, 'b')`

	variables := map[string]interface{}{`car`: `byd`}
	result, err := Evaluate(expr, variables)
	if err != nil {
		panic(err)
	}
	fmt.Println(result)
	// Output:
	// true
}

with custom functions

func ExampleParseAndEvaluate() {
	expr := `$car in ('bwm', 'byd') and (3 + echo_int(2)) * 2.0 = 10 and startsWith($car, 'b')`
	var tInt = func(a int64) int64 {
		return a
	}
	if err := RegisterFunc(`echo_int`, tInt); err != nil {
		panic(err)
	}

	variables := map[string]interface{}{`car`: `byd`}
	result, err := Evaluate(expr, variables)
	if err != nil {
		panic(err)
	}
	fmt.Println(result)
	// Output:
	// true
}