gorule

GoRule

Gorule is a rules engine written based on goyacc. The rule engine is mainly used to replace complex and frequently changed hard-coded conditional judgement scenarios. The rules defining the trigger conditions are decoupled from the program code and can be stored in files, database records etc. and loaded at runtime for parsing. The program provides input to the rules engine, which eventually matches and returns a collection of successful rules.

This project is licensed under the terms of the MIT license.

Usage

go get -u github.com/spikewong/gorule

Minimal example:

engine := gorule.NewEngine(
    gorule.WithLogger(log.New(os.Stdout, "", log.LstdFlags)),
    gorule.WithConfig(&gorule.Config{SkipBadRuleDuringMatch: false}),
)
rule := gorule.NewRule(
	"example rule name", "isAgeMatched(age) && undergraduate", 
	func(i interface{}) (interface{}, error) {
		return "teenager", nil
	})

err := engine.AddRule(rule)
if err != nil {
	fmt.Printf("add rule error: %v", err)
}

isAgeMatched := func(args ...interface{}) (interface{}, error) {
	age := args[0].(int)
	
	return age > 10 && age < 18, nil
}


rules, err := engine.Match(
	map[string]interface{}{ "age": 12, "undergraduate": true },
	map[string]parser.ExpressionFunction{
        "isAgeMatched": isAgeMatched,
    })
if err != nil {
    fmt.Printf("engine match error: %v", err)
}

for _, v := range rules {
    fmt.Println(v.Execute(nil))  // return "teenager", nil
}

you can find another example under examples directory

Supported rule expressions

Types

This library fully supports the following types: nil, bool, int, float64, string, []interface{} (=arrays) and map[string]interface{} (=objects).

Within expressions, int and float64 both have the type number and are completely transparent.
If necessary, numerical values will be automatically converted between int and float64, as long as no precision is lost.

Arrays and Objects are untyped. They can store any other value ("mixed arrays").

Structs are note supported to keep the functionality clear and manageable. They would introduce too many edge cases and loose ends and are therefore out-of-scope.

Variables

It is possible to directly access custom-defined variables. Variables are read-only and cannot be modified from within expressions.

Examples:

var
var.field
var[0]
var["field"]
var[anotherVar]

var["fie" + "ld"].field[42 - var2][0]

Functions

It is possible to call custom-defined functions from within expressions.

Examples:

rand()
floor(42)
min(4, 3, 12, max(1, 3, 3))
len("te" + "xt")

Literals

Any literal can be defined within expressions. String literals can be put in double-quotes " or back-ticks `. Hex-literals start with the prefix 0x.

Examples:

nil
true
false
3
3.2
"Hello, 世界!\n"
"te\"xt"
`te"xt`
[0, 1, 2]
[]
[0, ["text", false], 4.2]
{}
{"a": 1, "b": {c: 3}}
{"key" + 42: "value"}
{"k" + "e" + "y": "value"}

0xA                 // 10
0x0A                // 10
0xFF                // 255 
0xFFFFFFFF          // 32bit appl.: -1  64bit appl.: 4294967295
0xFFFFFFFFFFFFFFFF  // 64bit appl.: -1  32bit appl.: error

It is possible to access elements of array and object literals:

Examples:

[1, 2, 3][1]                // 2
[1, [2, 3, 42][1][2]        // 42

{"a": 1}.a                  // 1
{"a": {"b": 42}}.a.b        // 42
{"a": {"b": 42}}["a"]["b"]  // 42

Precedence

Operator precedence strictly follows C/C++ rules.

Parenthesis () is used to control precedence.

Examples:

1 + 2 * 3    // 7
(1 + 2) * 3  // 9

Operators

Arithmetic

Arithmetic + - * /

If both sides are integers, the resulting value is also an integer. Otherwise, the result will be a floating point number.

Examples:

3 + 4               // 7
2 + 2 * 3           // 8
2 * 3 + 2.5         // 8.5
12 - 7 - 5          // 0
24 / 10             // 2
24.0 / 10           // 2.4

Modulo %

If both sides are integers, the resulting value is also an integer. Otherwise, the result will be a floating point number.

Examples:

4 % 3       // 1
144 % 85    // -55
5.5 % 2     // 1.5
10 % 3.5    // 3.0

Negation - (unary minus)

Negates the number on the right.

Examples:

-4       // -4
5 + -4   // 1
-5 - -4  // -1
1 + --1  // syntax error
-(4+3)   // -7
-varName

Concatenation

String concatenation +

If either the left or right side of the + operator is a string, a string concatenation is performed. Supports strings, numbers, booleans and nil.

Examples:

"text" + 42     // "text42"
"text" + 4.2    // "text4.2"
42 + "text"     // "42text"
"text" + nil    // "textnil"
"text" + true   // "texttrue"

Array concatenation +

If both sides of the + operator are arrays, they are concatenated

Examples:

[0, 1] + [2, 3]          // [0, 1, 2, 3]
[0] + [1] + [[2]] + []   // [0, 1, [2]]

Object concatenation +

If both sides of the + operator are objects, their fields are combined into a new object. If both objects contain the same keys, the value of the right object will override those of the left.

Examples:

{"a": 1} + {"b": 2} + {"c": 3}         // {"a": 1, "b": 2, "c": 3}
{"a": 1, "b": 2} + {"b": 3, "c": 4}    // {"a": 1, "b": 3, "c": 4}
{"b": 3, "c": 4} + {"a": 1, "b": 2}    // {"a": 1, "b": 2, "c": 4}

Logic

Equals ==, NotEquals !=

Performs a deep-compare between the two operands. When comparing int and float64, the integer will be cast to a floating point number.

Comparisons <, >, <=, >=

Compares two numbers. If one side of the operator is an integer and the other is a floating point number, the integer number will be cast. This might lead to unexpected results for very big numbers which are rounded during that process.

Examples:

3 <-4        // false
45 > 3.4     // false
-4 <= -1     // true
3.5 >= 3.5   // true

And &&, Or ||

Examples:

true && true             // true
false || false           // false
true || false && false   // true
false && false || true   // true

Not !

Inverts the boolean on the right.

Examples:

!true       // false
!false      // true
!!true      // true
!varName

Ternary ? :

If the expression resolves to true, the operator resolves to the left operand.
If the expression resolves to false, the operator resolves to the right operand.

Examples:

true  ? 1 : 2                         // 1
false ? 1 : 2                         // 2
	
2 < 5  ? "a" : 1.5                    // "a"
9 > 12 ? "a" : [42]                   // [42]

false ? (true ? 1:2) : (true ? 3:4)   // 3

Note that all operands are resolved (no short-circuiting). In the following example, both functions are called (the return value of func2 is simply ignored):

true ? func1() : func2()

Bit Manipulation

Logical Or |, Logical And &, Logical XOr ^

If one side of the operator is a floating point number, the number is cast to an integer if possible. If decimal places would be lost during that process, it is considered a type error. The resulting number is always an integer.

Examples:

8 | 2          // 10
9 | 5          // 13
8 | 2.0        // 10
8 | 2.1        // type error

13 & 10        // 8
10 & 15.0 & 2  // 2

13 ^ 10        // 7
10 ^ 15 ^ 1    // 4

Bitwise Not ~

If performed on a floating point number, the number is cast to an integer if possible. If decimal places would be lost during that process, it is considered a type error. The resulting number is always an integer.

The results can differ between 32bit and 64bit architectures.

Examples:

~-1                   // 0
(~0xA55A) & 0xFFFF    // 0x5AA5
(~0x5AA5) & 0xFFFF    // 0xA55A

~0xFFFFFFFF           // 64bit appl.: 0xFFFFFFFF 00000000; 32bit appl.: 0x00
~0xFFFFFFFF FFFFFFFF  // 64bit appl.: 0x00; 32bit: error

Bit-Shift <<, >>

If one side of the operator is a floating point number, the number is cast to an integer if possible. If decimal places would be lost during that process, it is considered a type error. The resulting number is always an integer.

When shifting to the right, sign-extension is performed. The results can differ between 32bit and 64bit architectures.

Examples:

1 << 0    // 1
1 << 1    // 2
1 << 2    // 4
8 << -1   // 4
8 >> -1   // 16

1 << 31   // 0x00000000 80000000   64bit appl.: 2147483648; 32bit appl.: -2147483648
1 << 32   // 0x00000001 00000000   32bit appl.: 0 (overflow)

1 << 63   // 0x80000000 00000000   32bit appl.: 0 (overflow); 64bit appl.: -9223372036854775808
1 << 64   // 0x00000000 00000000   0 (overflow)

0x80000000 00000000 >> 63     // 0xFFFFFFFF FFFFFFFF   64bit: -1 (sign extension); 32bit: error (cannot parse number literal)
0x80000000 >> 31              // 64bit: 0x00000000 0000001; 32bit: 0xFFFFFFFF (-1, sign extension)

More

Array contains in

Returns true or false whether the array contains a specific element.

Examples:

"txt" in [nil, "hello", "txt", 42]   // true
true  in [nil, "hello", "txt", 42]   // false
nil   in [nil, "hello", "txt", 42]   // true
42.0  in [nil, "hello", "txt", 42]   // true
2         in [1, [2, 3], 4]          // false
[2, 3]    in [1, [2, 3], 4]          // true
[2, 3, 4] in [1, [2, 3], 4]          // false

Substrings [a:b]

Slices a string and returns the given substring. Strings are indexed byte-wise. Multi-byte characters need to be treated carefully.

The start-index indicates the first byte to be present in the substring.
The end-index indicates the last byte NOT to be present in the substring.
Hence, valid indices are in the range [0, len(str)].

Examples:

"abcdefg"[:]    // "abcdefg"
"abcdefg"[1:]   // "bcdefg"
"abcdefg"[:6]   // "abcdef"
"abcdefg"[2:5]  // "cde"
"abcdefg"[3:4]  // "d"

// The characters 世 and 界 both require 3 bytes:
"Hello, 世界"[7:13]    // "世界"
"Hello, 世界"[7:10]    // "世"
"Hello, 世界"[10:13]   // "界"

Array Slicing [a:b]

Slices an array and returns the given subarray.

The start-index indicates the first element to be present in the subarray.
The end-index indicates the last element NOT to be present in the subarray.
Hence, valid indices are in the range [0, len(arr)].

Examples:

// Assuming `arr := [0, 1, 2, 3, 4, 5, 6]`:
arr[:]    // [0, 1, 2, 3, 4, 5, 6]
arr[1:]   // [1, 2, 3, 4, 5, 6]
arr[:6]   // [0, 1, 2, 3, 4, 5]
arr[2:5]  // [2, 3, 4]
arr[3:4]  // [3]