Support variable

[dugenkui03]

background

Sometimes we want to pass some context, for example min price for commodity, and minPrice may be variable instead of static value. Introduce variables into expression will be more convenient.

proposal

enable evaluates the value with the given env.

demo

func TestExprWithEnv(t *testing.T) {
	var cases = []struct {
		expr string
		val  interface{}
	}{
		// env: a = 10, b = "string value",
		{expr: "a", val: 10.0},
		{expr: "b", val: "string value"},
		{expr: "a>10", val: false},
		{expr: "a<11", val: true},
		{expr: "a+1", val: 11.0},
		{expr: "a==10", val: true},
	}

	for _, c := range cases {
		t.Log(c.expr)
		vm, err := parseExpr(c.expr)
		if err != nil {
			t.Fatal(err)
		}
		val := vm.runWithEnv("", nil, map[string]interface{}{"a": 10, "b": "string value"})
		if !reflect.DeepEqual(val, c.val) {
			if f, ok := c.val.(float64); ok && math.IsNaN(f) && math.IsNaN(val.(float64)) {
				continue
			}
			t.Fatalf("expr: %q, got: %v, expect: %v", c.expr, val, c.val)
		}
	}
}