// Copyright 2020 Google LLC // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. package examples import ( "fmt" "log" "github.com/google/cel-go/cel" "github.com/google/cel-go/common/types" "github.com/google/cel-go/common/types/ref" ) func ExampleCustomInstanceFunction() { env, err := cel.NewEnv(cel.Lib(customLib{})) if err != nil { log.Fatalf("environment creation error: %v\n", err) } // Check iss for error in both Parse and Check. ast, iss := env.Compile(`i.greet(you)`) if iss.Err() != nil { log.Fatalln(iss.Err()) } prg, err := env.Program(ast) if err != nil { log.Fatalf("Program creation error: %v\n", err) } out, _, err := prg.Eval(map[string]any{ "i": "CEL", "you": "world", }) if err != nil { log.Fatalf("Evaluation error: %v\n", err) } fmt.Println(out) // Output:Hello world! Nice to meet you, I'm CEL. } type customLib struct{} func (customLib) CompileOptions() []cel.EnvOption { return []cel.EnvOption{ cel.Variable("i", cel.StringType), cel.Variable("you", cel.StringType), cel.Function("greet", cel.MemberOverload("string_greet_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType, cel.BinaryBinding(func(lhs, rhs ref.Val) ref.Val { return types.String( fmt.Sprintf("Hello %s! Nice to meet you, I'm %s.\n", rhs, lhs)) }), ), ), } } func (customLib) ProgramOptions() []cel.ProgramOption { return []cel.ProgramOption{} }