Cycles

There is no special syntax for cycles in niva, everything is a message send.

For loops

1..3 forEach: [ it echo ] // 1 2 3
1..<3 forEach: [ it echo ] // 1 2

Here .. is a binary message for Int that creates IntRange.
And IntRange can receive forEach: message.

with indexing:

3..5 forEachIndexed: [i, it ->
    "index: $i" echo
    "value $it" echo
]

The type signature of forEachIndexed here is
IntRange forEachIndexed: [Int, Int -> Any]
Which means that it takes a codeblock that receive 2 parameters, one of them is index and second is the number itself.

With custom steps:

1 to: 10 by: 2 do: [it echo]
// 1 3 5 7 9

While loop

While loop is just a message for the codeblock:
[ -> Boolean] whileTrue: [ -> Unit]

// there is also whileFalse
mut x = 10
[x > 0] whileTrue: [
  x echo
  x <- x dec
]

Iterate over collections

{1 2 3} forEach: [it echo]

{1 2 3} forEachIndexed: [i, it ->
    "index: $i" echo
    "value $it" echo
]

Over map:

#{"a" 1 "b" 2 "c" 3} forEach: [ k, v ->
  k echo
  v echo
]

See collections chapter for more

Ranges

Here are some useful messages for ranges

(1..5) first // 1
(1..5) last // 5
(1..5 step: 2) contains: 3 // true
(1..<5) random // 2

Iterate with break

If you really need to break while iterating collection you can add this method to your codebase:

MutableList::T forEachBreak::[T -> Boolean] -> Unit = [
    this forEach: [
        // check that every iteration returns true
        // othervice return from the function
        forEachBreak T: it |> not => ^
    ]
]

And use it like:

{1 2 3 4 5} forEachBreak: [
    it echo
    it % 3 != 0 // last statement must be Boolean
] 

So it will print 1 2 3 and break 3 is divisible by 3 without a remainder.
Basically it can be replaced with whileTrue: msg

Last modified: 14 December 2024