Functions and Lifting

First-class functions, object and list lifting, and non-destructive override with with.

Source

examples/functions-and-lifting/main.rank

/// Demonstrates first-class functions, automatic lifting over lists and objects,
/// zipped list lifting, and the `with` patch operator.

shift_port = |delta: number, port: number| -> number {
  return port + delta
}

scale = |factor: number, value: number| -> number {
  return value * factor
}

add = |left: number, right: number| -> number {
  return left + right
}

ports = {
  api: 8080,
  worker: 9090,
  admin: 7070,
}

replica_counts = {
  api: 3,
  worker: 2,
  admin: 1,
}

base_ports = [8080, 8081, 8082]
rollout_offsets = [0, 100, 200]

base_service = {
  port: 3000,
  replicas: 1,
  debug: false,
}

dev_override = base_service with {
  debug: true,
}

prod_override = base_service with {
  replicas: 5,
}

pub main = || {
  shifted_ports: shift_port(10000, ports),
  scaled_replicas: scale(3, replica_counts),
  canary_ports: add(base_ports, rollout_offsets),
  dev: dev_override,
  prod: prod_override,
}

Output

{
  "shifted_ports": {
    "api": 18080,
    "worker": 19090,
    "admin": 17070
  },
  "scaled_replicas": {
    "api": 9,
    "worker": 6,
    "admin": 3
  },
  "canary_ports": [8080, 8181, 8282],
  "dev": {
    "port": 3000,
    "replicas": 1,
    "debug": true
  },
  "prod": {
    "port": 3000,
    "replicas": 5,
    "debug": false
  }
}

Key concepts

• Object lifting — shift_port(10000, ports) applies the same scalar function to every field of the object. No explicit traversal code is needed.
• Broadcast over structured values — scale(3, replica_counts) keeps the scalar 3 fixed while lifting across the object on the right.
• Zipped list lifting — add(base_ports, rollout_offsets) aligns both lists by position and applies add element-by-element.
• with patch — base_service with { debug: true } produces a new object identical to base_service except for the overridden fields. The original is never mutated.

Run it

rank examples/functions-and-lifting