Rule definition language reference

Introduction

ezrules allows writing rules in expressive language, which can roughly be described as python with add-ons. Having python backing the rule definition language, ezrules allow writing logic of any complexity. Technically speaking, whatever python can do, rules defined within ezrules can do too - complex conditional statements, loops, and any other language constructs.

Rule writing language

Referring to event variables

To refer to a top-level event variable, one can use $-notation. For example, if we have the following event defined:

{
   "amount": 900,
   "risk_score": 560
}

, then we can refer to those fields like this:

if $amount > 900 and $risk_score < 900:
  return "RELEASE"

Note, that we use the return statement to define what happens with the event if it matches the criteria in the rule definition.

Nested structures work too, one can write something like

if $customer["age"] > 25:
   return "HOLD"

Referring to globally defined lists

In the Lists section of the Manager UI, one can define globally available lists. Those lists can later be referred to by their name and @-notation, e.g.

if $origin_country in @NACountries:
   return "HOLD"

Possible return values are manageable and pre-defined

Only outcomes mentioned in Outcomes section are permitted in the return statements. If any other value is specified in the return, the rule will be rejected.

Afterword

Technically, what ezrules does behind the door with a rule, is it wraps it into a function definition with a single input parameter t. For example, if you wrote a rule of kind

if $amount > 900:
   return "HOLD"

internally it will transformed into

def rule(t):
   if t["amount"] > 900:
      return "HOLD"