Flow Control

Conditionals

if / else

if (score >= 70)
  echo pass
else
  echo fail

The condition is a compact expression or a full command:

if flag
  echo "flag is set"

if func "argument"
  echo success

else if

if (score >= 90)
  echo A
else if (score >= 80)
  echo B
else if (score >= 70)
  echo C
else
  echo F

if in let and Assignments

if statements can be the right-hand side of let bindings and assignments:

let max = if (a > b)
  a
else
  b

let msg = if (count == 0)
  "empty"
else if (count == 1)
  "one"
else
  "many"

# Also works with assignment
result = if error
  get_error_message $error
else
  data

Loops

while

let count = 0
while (count < 5)
  echo $count
  count = (count + 1)

for

Iterate over arrays, dictionaries, ranges, and other iterables:

for item = [1, 2, 3]
  echo $item

for pair = {name: "Alice", age: 30}
  echo $pair

for i = range 5
  echo $i

Dictionaries iterate as [key, value] pairs. Use destructuring to unpack them:

for k v = {name: "Alice", age: 30}
  echo "$k: $v"

See Destructuring for more on for unpacking.

Flow Control Statements

break

Exit the innermost loop.

for i = range 100
  if (i >= 5)
    break
  echo $i

break works through intervening do blocks:

def find_incomplete configs
  for config = configs
    config.get "host" else: do
      break
    process $config
  "done"

continue

Skip to the next iteration.

for i = range 10
  if (i % 2 == 0)
    continue
  echo $i  # prints odd numbers

continue works through intervening do blocks:

for item = items
  let id = item.get id else: do
    continue
  echo "Processing $id"

return

Return a value from a function early.

def find_first arr pred
  for item = arr
    if pred $item
      return item
  nil

let result = find_first [1, 2, 3, 4] do |x| (x > 2)
assert_eq $result 3

return exits the innermost enclosing def, even when called from within a do block:

def validate_record record
  for field = ["id", "name", "email"]
    record.get field else: do
      return {valid: false, missing: field}
  {valid: true}

let result = validate_record {name: "Alice", email: "alice@example.com"}
# Returns: {valid: false, missing: "id"}

throw

Raises an error, unwinding the call stack until the error is caught by a try/catch block.

throw "something went wrong"

See Error Handling for full details on raising and catching errors.