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recif: rule engine comme il faut

Rule engine parser that translates conditions from rule file in json or yaml format to native code.

Description

When businesses express new or updated rulesets, they may be either coded by programmers into the existing information system, or they may be declared in a special dialect that the system may parse and evaluate. In this case programmer's intervention is not needed, but the parsing and evaluation time may be significant. Each time the system needs to evaluate conditions from a ruleset for specific context (for example, define product segment) the system needs to parse the rule file, process conditions starting at the top level until the matching rule found, all this recursively calling methods for each operation mentioned in a ruleset.

With recif, when rulesets are updated in a rule file we call the converter that translates the rules into a native code. That code represents the ruleset conditions from the file. All operations are already translated to native constructs like OR, AND etc, so the execution of the full ruleset is optimal. To use that class inside your project instantiate the object and call its evaluate() method passing the context as its parameter. evaluate() will return true (or corresponding value) if match found, or false if passed context does not match any condition (yes, you may provide your own return value).

Example 1

Single condition. Input context is a literal numeric value that is evaluated and returns true if it is greater than 10:

Example 2

Multiple conditions combined with AND operator. Input context is a literal numeric value. Returns true if context value is in the range 0..100:

Example 3

Complex conditions: context is an associative array with country and currency entries which must match the following matrix:

If condition matches it will return continent name for the context (North America or Europe) instead of simple true value.

Note: to represent an array you need to use a special {"_": ...} inline operator.

Installation

Require with composer:

Command line usage

After installation with composer, recif binary is available as vendor/bin/recif.

Simplest ruleset: evaluate the true statement:

Same level: evaluate that 1 > 0:

Do something meaningful: check context, add namespace to generated class and specify return type of its evaluate() method:

Syntax of rule files

Rule file contains a tree of conditions starting with a root condition.

Each condition is an object with a single required entry containing operation name as key and arguments as value. An optional return entry may contain returned value for the case if operation matches, otherwise the default true will be returned.

Operators like or must contain an array of arguments. Unary operators like not operate on a single value, not an array. See [Operations reference]() for the full list of available operations.

Each argument may have one of the following forms:

• literal value or array (normally used to compare the value with context field), like true or "US";
• object (representing context or another operation), like {"cx":"currency"} or {"eq": [{"cx":"country"}, "US"]} or {"_": ["DE", "ES", "FR", "IT"]}.

Returned value represents the value that is returned to the outer operation when the corresponding condition evaluates to true. It may be declared as any type. If value is an object, it may represent context or one of its properties, like {"cx":""} or {"cx":"currency.iso_name"}. In this case the value of this element or property will be returned.

Operations reference

Examples below are given in json notation, meanings are given as php code.

Context operator

cx - context value (argument: empty string if context is literal, dot-separated list of keys if array)

Example: {"cx":""}, {"cx":"url.path"}

Meaning: $context, $context['url']['path']

Comparison operators

eq - equal

Example: {"eq": [{"cx":""}, 0]}

Meaning: $context == 0

=== - identical (equal and same type)

Example: {"===": [{"cx":""}, '15h']}

Meaning: $context === '15h'

ne - not equal

Example: {"ne": [{"cx":""}, 0]}

Meaning: $context != 0

!== - not identical (not equal or different type)

Example: {"!==": [{"cx":""}, '15h']}

Meaning: $context !== '15h'

lt - less than

Example: {"lt": [{"cx":""}, 0]}

Meaning: $context < 0

le - less or equal

Example: {"le": [{"cx":""}, 0]}

Meaning: $context <= 0

gt - greater than

Example: {"gt": [{"cx":""}, 0]}

Meaning: $context > 0

ge - greater or equal

Example: {"ge": [{"cx":""}, 0]}

Meaning: $context >= 0

Logical operators

or - or (two or more arguments)

Example: {"or": [{"eq": [{"cx":""}, 0]}, {"eq": [{"cx":""}, 10]}]}

Meaning: ($context == 0) or ($context == 10)

and - and (two or more arguments)

Example: {"and": [{"gt": [{"cx":""}, 0]}, {"lt": [{"cx":""}, 10]}]}

Meaning: ($context > 0) and ($context < 10)

not - not (unary operator, single argument)

Example: {"not": {"lt": [{"cx":""}, 0]}}

Meaning: ! ($context < 0)

Math operations

mod - modulo (arguments: value, modulo)

Example: {"mod": [{"cx":""}, 10]}

Meaning: $context % 10

rnd - random integer number within range (arguments: min, max)

Example: {"rnd": [1, 10]}

Meaning: rand(1, 10)

Array operations

in - element exists in array (arguments: element, array)

Example: {"in": [{"cx":""}, {"_": [1, 2, 3, 5, 8, 13]}]}

Meaning: in_array($context, [1, 2, 3, 5, 8, 13])

inx - get element from hash map by index (arguments: index, hash map)

Example: {"inx": [{"cx":""}, {"_": ["FR": "Europe", "US": "North America"]}]}, {"inx": [{"cx":""}, {"_": ["US": "North America", "default": "Europe"]}]}

Meaning: (["FR" => "Europe", "US" => "North America"])[$context], (["US" => "North America"])[$context] ?? "Europe"

String operations

sub - needle substring exists in haystack string (arguments: needle, haystack). Search in Unicode case-insensitive mode.

Example: {"sub": ["word", {"cx":""}]}

Meaning: mb_stripos($context, "word") !== false

re - string matches regular expression (arguments: regex, text).

Example: {"re": ["/^\w+$/u", {"cx":""}]}

Meaning: preg_match('/^\w+$/u', $context)

spf - formatted string a.k.a. sprintf (arguments: format string, zero or more values).

Example: {"spf": ["%.2f", {"cx":""}]}

Meaning: sprintf('%.2f', $context)

Inline operator

_ (underscore) - uses argument value as is (argument of any type).

Example: {"_": true}, {"_": ["a": "b"]}, {"_": [1, {"_": []}, 3]}

Meaning: true, ['a' => 'b'], [1, [], 3]

Native function call

fn - calls native function with provided params (arguments: function name, param1, ...).

Example: {"fn": ["Currencies::getRateForCountry", {"cx":"country"}]}

Meaning: Currencies::getRateForCountry($context['country'])

Code examples

Example 1

Rule file:

Generated code:

For the following examples the generated code will be created inside the Ruleset::evaluate() method, like in the example above, so only the corresponding // rules part will be presented.

Example 2

Rule file:

Generated code:

Example 3

Rule file:

Generated code:

REMARK In php-5 compatibility mode, the ($context['currency'] ?? null) and similar constructs will be replaced by isset($context['currency']) and $context['currency'] constructs.