Rules - Point docs

Summary

A rule expresses logic that accumulates into an output: totals, scores, and conditional adds. The same pattern models cart totals, fraud risk, SLA points, or eligibility — not only marketing checklists.

Syntax

record Cart Item
  unit price: Int
  quantity: Int

rule cart total
  input items: List<Cart Item>
  output total: Int
  total starts at 0
  for each item in items
  add item.unit price * item.quantity to total
  return total

Semantics

output name starts at expr initializes mutable state
add N when condition adds to the output when the condition is true
for each item in list iterates; add X to Y mutates accumulators
return finishes the rule

Compiler note

Rules use mutable accumulators (starts at, add when, loops). The checker validates input types and field access on each condition.

Example

From examples/cart-total.point:

module Checkout

record Cart Item
  name: Text
  unit price: Int
  quantity: Int

calculation line total
  input item: Cart Item
  output total: Int
  total is item.unit price * item.quantity

rule cart total
  input items: List<Cart Item>
  output total: Int
  total starts at 0
  for each item in items
  add item.unit price * item.quantity to total
  return total

For conditional scoring without loops, see examples/adopters/starter-labs/subscription-tier.point.

Common mistakes

Using add N when on a calculation (rules only)
Iterating a non-list (iteration-type-mismatch)

Agent diagnostic notes

Output names in rules avoid duplicate suffixes on the lowered symbol (cart total + output total stays readable, not cartTotalTotal)
Ref: point://semantic/<Module>/rule.<name>