CESQL user defined function support

[csc-piscopo]

Docs seem to indicate adding a user defined function is available and supported but I can't get this to work: (lifted from the README)

package main

import (
	"fmt"
	"os"
	"strings"

	cesql "github.com/cloudevents/sdk-go/sql/v2"
	cefn "github.com/cloudevents/sdk-go/sql/v2/function"
	cesqlparser "github.com/cloudevents/sdk-go/sql/v2/parser"
	ceruntime "github.com/cloudevents/sdk-go/sql/v2/runtime"
	cloudevents "github.com/cloudevents/sdk-go/v2"
)

func main() {
	// Create a test event
	event := cloudevents.NewEvent()
	event.SetID("aaaa-bbbb-dddd")
	event.SetSource("https://my-source")
	event.SetType("dev.tekton.event")

	// Create and add a new user defined function
	var HasPrefixFunction cesql.Function = cefn.NewFunction(
		"HASPREFIX",
		[]cesql.Type{cesql.StringType, cesql.StringType},
		nil,
		func(event cloudevents.Event, i []interface{}) (interface{}, error) {
			str := i[0].(string)
			prefix := i[1].(string)

			return strings.HasPrefix(str, prefix), nil
		},
	)

	err := ceruntime.AddFunction(HasPrefixFunction)

	// parse the expression
	expression, err := cesqlparser.Parse("HASPREFIX(type, 'dev.tekton.event')")
	if err != nil {
		fmt.Println("parser err: ", err)
		os.Exit(1)
	}

	// Evalute the expression with the test event
	res, err := expression.Evaluate(event)

	if res.(bool) {
		fmt.Println("Event type has the prefix")
	} else {
		fmt.Println("Event type doesn't have the prefix")
	}
}

Referencing v2.15.2 for the sdk. Maybe I am missing something obvious, thanks!