Variables¶

In RuLa, variables that bind to case instances — such as p is Person — are called declarations. This page is about the other kind: value variables, which let you capture any intermediate result and give it a name inside the assignment part of a rule.

What Are Value Variables?¶

A value variable holds the result of any expression: a number, string, list, dictionary, date, and so on. You define one with :=, giving it a plain name on the left and the expression on the right.

p is Person
---
full_name := CONCAT(p.first_name, ' ', p.last_name)
p.display_name := full_name

full_name is a value variable. It is computed once and then reused on the next line. Without it, you would have to write the CONCAT(...) expression twice.

Info

A value variable is local to the rule it is defined in. It is available on all lines that follow its definition, but it does not persist between rules.

Syntax¶

left_side := right_side

Left side — determines what receives the value:

A plain name (e.g. net_worth) creates a local variable available on subsequent lines in the same rule.
A field path (e.g. p.net_worth) writes the value into that information field on the instance.

Right side — any expression that produces a value: a calculation, a string operation, a conditional expression, a list, a dictionary, and so on.

Examples¶

Storing a calculated value to reuse it¶

p is Person
---
net_worth := p.total_assets - p.total_liabilities
p.net_worth := net_worth
p.risk_score := if net_worth < 0 then high_risk else low_risk end

net_worth is computed once and referenced twice — once to store the figure and once to derive the risk score from it.

Cleaning up a string before assignment¶

p is Person
---
normalised := UPPER(TRIM(p.first_name))
p.first_name_normalised := normalised

The raw value of first_name is trimmed of whitespace and uppercased. The cleaned result is stored in a variable and then written to a separate field.

Building a list incrementally¶

p is Person
---
base_docs := ['id_copy', 'proof_of_address']
full_docs := if p.nationalities contains us then APPEND(base_docs, 'w8_form') else base_docs end
p.required_documents := full_docs

base_docs holds the default document list. full_docs extends it conditionally. The final list is then assigned to the field.

Using a variable across multiple assignments¶

c is Contract
p is Person
---
annual_fee := c.aum * 0.0075
p.expected_fee := if annual_fee > 10000 then annual_fee else 10000 end

annual_fee is derived from the contract and then used in an if-then-else to enforce a fee floor before being written to the person.

Intermediate dictionary for a structured assignment¶

p is Person
---
address := {"street": p.street, "city": p.city, "country": p.domicile}
p.formatted_address := PRETTY_PRINT(address)

A dictionary is assembled from several fields into address, which is then formatted and stored.

Naming Variables¶

Variable names:

Must start with a letter.
Can contain letters, digits, and underscores.
Are case-sensitive (NetWorth and net_worth are two different variables).
Should be short but descriptive — the goal is to make the rule easier to read, not harder.