Examples

Each example isolates a syntax or runtime rule. The language reference contains the full semantics and constraints.

Hello

print("hello, Nilakan")

Output: "hello, Nilakan"

Typed Function

def area(width: num, height: num) -> num:
  return width * height

print(area(4, 5))

Output: 20

Collections

xs = [1, 2].append(3)
print(xs)

seen = {"a", "b"}
print("a" in seen)

counts = {"a": 1}
print(counts.set("b", 2))

Output:

[1, 2, 3]
True
{"a": 1, "b": 2}

Simultaneous Update

def exchange() -> tuple[num, num]:
  init:
    left = 1
    right = 2
    done = False
  while not done:
    left' = right
    right' = left
    done' = True
  return left, right

print(exchange())

Output: (2, 1). Both right-hand sides read the same current state.

Sparse List Update

def swap_edges(values: list[num]) -> list[num]:
  init:
    arr = values
    step = 0
  while step < 1:
    arr'[0] = arr[2]
    arr'[2] = arr[0]
    step' = step + 1
  return arr

print(swap_edges([1, 2, 3]))

Output: [3, 2, 1]. Both sparse writes read the same frozen pre-round list.

RHS-Prime Loop

def accumulate() -> list[num]:
  init:
    xs = [1, 2]
    step = 0
  pragma rhs_prime: idempotent
  while step < 1:
    xs'[1] = xs'[0] + 1
    xs'[0] = 11 if xs[0] < 11 else xs[0]
    step' = 1
  return xs

print(accumulate())

Output: [11, 12]. Dependency scheduling evaluates the write to index 0 before the primed read used for index 1.

Type Contract Failure

Intentional failure — NLK2011

value: num = "not a number"

Expected result: a fatal TypeError/NLK2011 contract diagnostic; this example intentionally does not run successfully.

Error Values And Catch

def first_or_error(xs: list[num]) -> num | err:
  return try xs.get(0)

def safe_first(xs: list[num]) -> num:
  return first_or_error(xs) catch 0

print(safe_first([]))

Output: 0. The missing index becomes IndexError/NLK4004, which catch replaces.