Pipes and Collections

The pipe operator |> with map, filter, reduce, groupBy, sortBy, and keyBy.

Source

examples/pipes-and-collections/main.rank

/// Demonstrates the pipe operator and stdlib collection functions:
/// map, filter, reduce, groupBy, sortBy, and keyBy.

use std::collections::{ map, filter, reduce, groupBy, sortBy, keyBy }
use std::object::{ mapValues }

Service = Object {
  name: string,
  team: string,
  port: number,
  replicas: number,
}

services: [Service] = [
  { name: `api`, team: `backend`, port: 8080, replicas: 3 },
  { name: `worker`, team: `backend`, port: 9090, replicas: 2 },
  { name: `web`, team: `frontend`, port: 3000, replicas: 4 },
  { name: `admin`, team: `frontend`, port: 7070, replicas: 1 },
]

active_services = services |> filter(|svc: Service| svc.replicas > 1)

named_services = services |> map(|svc: Service| `${svc.name}:${svc.team}`)

total_replicas = services |> reduce(0, |acc: number, svc: Service| acc + svc.replicas)

by_team = services |> groupBy(|svc: Service| svc.team)

by_name = services |> keyBy(|svc: Service| svc.name)

sorted_by_port = services |> sortBy(|svc: Service| svc.port)

replica_map = services
  |> keyBy(|svc: Service| svc.name)
  |> mapValues(|svc: Service, name: string| svc.replicas)

pub main = || {
  active_services,
  named_services,
  total_replicas,
  by_team,
  by_name,
  sorted_by_port,
  replica_map,
}

Output

{
  "active_services": [
    { "name": "api", "team": "backend", "port": 8080, "replicas": 3 },
    { "name": "worker", "team": "backend", "port": 9090, "replicas": 2 },
    { "name": "web", "team": "frontend", "port": 3000, "replicas": 4 }
  ],
  "named_services": ["api:backend", "worker:backend", "web:frontend", "admin:frontend"],
  "total_replicas": 10,
  "by_team": {
    "backend": [
      { "name": "api", "team": "backend", "port": 8080, "replicas": 3 },
      { "name": "worker", "team": "backend", "port": 9090, "replicas": 2 }
    ],
    "frontend": [
      { "name": "web", "team": "frontend", "port": 3000, "replicas": 4 },
      { "name": "admin", "team": "frontend", "port": 7070, "replicas": 1 }
    ]
  },
  "sorted_by_port": [
    { "name": "web", "team": "frontend", "port": 3000, "replicas": 4 },
    { "name": "admin", "team": "frontend", "port": 7070, "replicas": 1 },
    { "name": "api", "team": "backend", "port": 8080, "replicas": 3 },
    { "name": "worker", "team": "backend", "port": 9090, "replicas": 2 }
  ],
  "replica_map": { "api": 3, "worker": 2, "web": 4, "admin": 1 }
}

Key concepts

• Pipe |> — services |> filter(...) passes services as the first argument to filter. Chains read left-to-right.
• groupBy — partitions a list into an object whose keys are the return values of the callback.
• keyBy — like groupBy but asserts each key appears exactly once, returning an object of single values.
• mapValues — transforms only the values of an object, leaving keys intact.
• reduce — folds a list to a single value. The accumulator type is inferred from the initial argument.

Run it

rank examples/pipes-and-collections