1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
|
// Copyright 2019 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 cel_test
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 Example() {
// Create the CEL environment with declarations for the input attributes and the extension functions.
// In many cases the desired functionality will be present in a built-in function.
e, err := cel.NewEnv(
// Variable identifiers used within this expression.
cel.Variable("i", cel.StringType),
cel.Variable("you", cel.StringType),
// Function to generate a greeting from one person to another: i.greet(you)
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))
}),
),
),
)
if err != nil {
log.Fatalf("environment creation error: %s\n", err)
}
// Compile the expression.
ast, iss := e.Compile("i.greet(you)")
if iss.Err() != nil {
log.Fatalln(iss.Err())
}
// Create the program.
prg, err := e.Program(ast)
if err != nil {
log.Fatalf("program creation error: %s\n", err)
}
// Evaluate the program against some inputs. Note: the details return is not used.
out, _, err := prg.Eval(map[string]interface{}{
// Native values are converted to CEL values under the covers.
"i": "CEL",
// Values may also be lazily supplied.
"you": func() ref.Val { return types.String("world") },
})
if err != nil {
log.Fatalf("runtime error: %s\n", err)
}
fmt.Println(out)
// Output:Hello world! Nice to meet you, I'm CEL.
}
func Example_globalOverload() {
// The GlobalOverload example demonstrates how to define global overload function.
// Create the CEL environment with declarations for the input attributes and
// the desired extension functions. In many cases the desired functionality will
// be present in a built-in function.
e, err := cel.NewEnv(
// Identifiers used within this expression.
cel.Variable("i", cel.StringType),
cel.Variable("you", cel.StringType),
// Function to generate shake_hands between two people.
// shake_hands(i,you)
cel.Function("shake_hands",
cel.Overload("shake_hands_string_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
cel.BinaryBinding(func(arg1, arg2 ref.Val) ref.Val {
return types.String(fmt.Sprintf("%v and %v are shaking hands.\n", arg1, arg2))
}),
),
),
)
if err != nil {
log.Fatalf("environment creation error: %s\n", err)
}
// Compile the expression.
ast, iss := e.Compile(`shake_hands(i,you)`)
if iss.Err() != nil {
log.Fatalln(iss.Err())
}
// Create the program.
prg, err := e.Program(ast)
if err != nil {
log.Fatalf("program creation error: %s\n", err)
}
// Evaluate the program against some inputs. Note: the details return is not used.
out, _, err := prg.Eval(map[string]interface{}{
"i": "CEL",
"you": func() ref.Val { return types.String("world") },
})
if err != nil {
log.Fatalf("runtime error: %s\n", err)
}
fmt.Println(out)
// Output:CEL and world are shaking hands.
}
|
