expr's Introduction

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
}

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