Control flow

Hetu has while, do loops, and classic for(init;condition;increment) and for...in loops. As well as when statement, which works like switch.

fun main {
  var i = 0
  for (;;) {
    ++i
    when (i % 2) {
      0 -> print('even:', i)
      1 -> print('odd:', i)
      else -> print('never going to happen.')
    }
    if (i > 5) {
      break
    }
  }
}

If

if statement's branches could be a single statement without brackets.

if (condition) {
  ...
} else {
  ...
}

if can also be an expression which will have a value, in this case else branch is not omitable.

Loop

Syntax for loop statement is the same to most C++/Java like languages.

You can use break and continue within them.

While

while (condition) {
  ...
}

Do

do {
  ...
} while (condition)

'do' statement's 'while' part is optional, if omitted, it will become a anonymous code block. It's kind of like an anonymous function that immediately calls.

For

'for' statement's expr must be separated with ';'.

The expression itself is optional. If you write 'for ( ; ; )', it will be the same to 'while (true)'

When use for...in, the loop will iterate through the keys of a list.

When use for...of, the loop will iterate through the values of a struct literal/Dart Map.

for (init; condition; increment) {
  ...
}

for (var item in list) {
  ...
}

for (var item of obj) {
  ...
}

When

When is the substitue for 'switch' in older programming languages, we change its name to indicate more complex usages.

'when' statement's condition is optional. If not provided, the interpreter will check the cases and jump to the first branch if the expression evaled as true, just like a if else statement.

However for when statement's cases, interpreter won't inexplicitly convert non-boolean values.

'when' statement's case could be non-const expression or variables;

'when' statement's body must be enclosed in curly brackets. However, the case branch could be a single statement without brackets;

'when' statement's else branch is optional.

If you want to match multiple values in one branch, use comma expression.

If you want to check if an iterable/object contains the value, use in/of expression.

for (final i in range(0, 10)) {
  when (i) {
    0 -> {
      print('number: 0')
    }
    2, 3, 5, 7 -> {
      print('prime: ${i}')
    }
    in [4, 9] -> {
      print('square: ${i}')
    }
    else -> {
      print('other: ${i}')
    }
  }
}