examples

your first program — variables, strings and string math

// Welcome to Lumen ✦
let name = "world"
print("Hello, " + name + "!")
print("Lumen " * 3)

filter, map and sum a list in one readable chain

// |> passes the value on the left as the first argument
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  |> filter(fn(n) { n % 2 == 0 })
  |> map(fn(n) { n * n })
  |> sum
  |> print

recursion, where a function returns its last line

fn fib(n) {
  if n < 2 { n } else { fib(n - 1) + fib(n - 2) }
}
for i in range(15) {
  print("fib(" + i + ") =", fib(i))
}

if/else as a value, right inside a loop

for i in range(1, 21) {
  let out = if i % 15 == 0 { "FizzBuzz" }
    else if i % 3 == 0 { "Fizz" }
    else if i % 5 == 0 { "Buzz" }
    else { i }
  print(out)
}

a function that remembers its own counter

fn counter() {
  let count = 0
  fn() { count += 1; count }
}
let tick = counter()
tick(); tick()
print("ticked", tick(), "times")

named values, updates and walking the keys

let hero = { name: "Ada", level: 7, skills: ["logic", "poetry"] }
hero.level += 1
print(hero.name, "is level", hero.level)
for key in hero { print(" -", key, "=>", hero[key]) }

while loops, early return and a pipe to the finish

fn is_prime(n) {
  if n < 2 { return false }
  let i = 2
  while i * i <= n {
    if n % i == 0 { return false }
    i += 1
  }
  true
}
range(2, 60) |> filter(is_prime) |> join(", ") |> print

read structured data, transform it, send JSON back

// Read structured data, transform it, send JSON back
let data = json_parse("{\"scores\":[12,3,25,8],\"name\":\"Ada\"}")
let top = data.scores |> sort |> reverse |> slice(0, 2)
print(data.name, "top scores:", top)
{ name: data.name, top: top } |> json_stringify |> print

sort objects, find the first match, ask any and every

let tasks = [
  { name: "parser", done: true, priority: 2 },
  { name: "compiler", done: false, priority: 1 },
  { name: "tests", done: true, priority: 3 }
]
tasks |> sort(fn(a, b) { a.priority - b.priority })
  |> map(fn(task) { task.name }) |> join(", ") |> print
print("next:", find(tasks, fn(task) { not task.done }).name)
print("all done:", every(tasks, fn(task) { task.done }))
print("some done:", any(tasks, fn(task) { task.done }))
let versions = { lumen: 1, tools: 2 }
print(has(versions, "lumen"), values(versions), entries(versions))

trim, replace, search and count words

// Text tools: shape, search and count words
let shout = "  hello lumen  " |> trim |> upper
print(shout)
print(replace("a-b-c", "-", " + "))
print(starts_with("lumen", "lu"), ends_with("lumen", "en"))
print(includes("glow", "low"), includes([1, 2, 3], 2))
let words = split("the glow of the code", " ")
print("the appears", count(words, fn(w) { w == "the" }), "times")

dedupe, flatten and pair up lists

// Reshape lists: dedupe, flatten, pair up
print(unique([1, 2, 2, 3, 1]))
print(flatten([[1, 2], [3], [4, 5]]))
print(zip(["a", "b", "c"], [1, 2, 3]))
let scores = [5, 120, 42, 300]
print(scores |> map(fn(s) { clamp(s, 0, 100) }))
print(pow(2, 10), clamp(7, 0, 5))

skip an iteration without leaving the loop

// Skip an iteration without leaving the loop
let total = 0
for n in range(1, 7) {
  if n % 2 == 0 { continue }
  total += n
}
print("odd total:", total)
let n = 0
while n < 5 {
  n += 1
  if n < 3 { continue }
  print(n)
}