Arrays

Complete array guide with literals, indexing, slicing, and all priyoArray helper functions.

Theory

Arrays are ordered collections used to store multiple values under one variable name. They solve repeated-data problems such as lists of marks, names, prices, matrix rows, and filtered search results. In PriyoScript, arrays are first-class values: you can create them, mutate them, slice them, iterate through them, and process them with helper methods. A strong array foundation is essential for writing practical programs.

Why arrays matter

If you are handling repeated values, arrays usually make the code shorter, safer, and easier to maintain.

Array Basics Table

Feature	Syntax	Description
Literal	`[1, 2, 3]`	Create an array
Index read	`arr[0]`	Read value at index
Index write	`arr[1] = 10`	Update index value
Slice	`arr[1:3]`	Extract subarray
For-each loop	`prakritiCount (item priyoInside arr)`	Iterate over elements

`priyoArray` Helper Functions Table

Core helpers

Helper	Signature	Returns
`length`	`priyoArray.length(arr)`	Number
`push`	`priyoArray.push(arr, value)`	New length
`pop`	`priyoArray.pop(arr)`	Removed value or `priyoEmpty`-like result
`first`	`priyoArray.first(arr)`	First value or `null`
`last`	`priyoArray.last(arr)`	Last value or `null`
`at`	`priyoArray.at(arr, index)`	Value at index or `null`
`slice`	`priyoArray.slice(arr, start?, end?)`	New array
`reverse`	`priyoArray.reverse(arr)`	New reversed array
`includes`	`priyoArray.includes(arr, value)`	Boolean
`indexOf`	`priyoArray.indexOf(arr, value)`	Index or `-1`
`join`	`priyoArray.join(arr, sep?)`	String

Callback helpers

Helper	Signature	Returns
`map`	`priyoArray.map(arr, callback)`	New mapped array
`filter`	`priyoArray.filter(arr, callback)`	New filtered array
`reduce`	`priyoArray.reduce(arr, callback, initial?)`	Accumulated value
`forEach`	`priyoArray.forEach(arr, callback)`	`null`
`find`	`priyoArray.find(arr, callback)`	Found value or `null`
`some`	`priyoArray.some(arr, callback)`	Boolean
`every`	`priyoArray.every(arr, callback)`	Boolean

Basic Array Syntax Examples

Example 1: Literal + index read/write

monalisa {
  priyoKeep nums = [10, 20, 30]
  priyoTell(nums[0])
  nums[1] = 25
  priyoTell(nums[1])
}

Output:

10
25

Example 2: Slicing

monalisa {
  priyoKeep nums = [10, 20, 30, 40]
  priyoTell(nums[1:3])
}

Output:

[20, 30]

Core Helper Examples (all functions)

monalisa {
  priyoKeep arr = [10, 20, 30]

  priyoTell(priyoArray.length(arr))
  priyoTell(priyoArray.push(arr, 40))
  priyoTell(priyoArray.pop(arr))
  priyoTell(priyoArray.first(arr))
  priyoTell(priyoArray.last(arr))
  priyoTell(priyoArray.at(arr, 1))
  priyoTell(priyoArray.at(arr, 99))
  priyoTell(priyoArray.slice(arr, 0, 2))
  priyoTell(priyoArray.reverse(arr))
  priyoTell(priyoArray.includes(arr, 20))
  priyoTell(priyoArray.indexOf(arr, 30))
  priyoTell(priyoArray.join(arr, "-"))
}

Output:

3
4
40
10
30
20
null
[10, 20]
[30, 20, 10]
priyoTrue
2
10-20-30

Callback Helper Examples (all functions)

monalisa {
  lisaaTask double(x) {
    priyoGiveBack x * 2
  }

  lisaaTask isEven(x) {
    priyoGiveBack x % 2 == 0
  }

  lisaaTask add(acc, x) {
    priyoGiveBack acc + x
  }

  lisaaTask printItem(x) {
    priyoTell("item=" + x)
  }

  priyoKeep vals = [1, 2, 3, 4]

  priyoTell(priyoArray.map(vals, double))
  priyoTell(priyoArray.filter(vals, isEven))
  priyoTell(priyoArray.reduce(vals, add, 0))
  priyoArray.forEach(vals, printItem)
  priyoTell(priyoArray.find(vals, isEven))
  priyoTell(priyoArray.some(vals, isEven))
  priyoTell(priyoArray.every(vals, isEven))
}

Output:

[2, 4, 6, 8]
[2, 4]
10
item=1
item=2
item=3
item=4
2
priyoTrue
priyoFalse

Invalid Usage Example

monalisa {
  priyoTell(priyoArray.length("not-array"))
}

Why invalid: first argument must be an array.
Expected error output:

priyoArray.length expects an array as the first argument

Practice Questions

Concept Check

What is the difference between priyoArray.slice(...) and priyoArray.reverse(...) in mutation behavior? 2. When should you use map vs forEach? 3. Why does find return null when nothing matches?

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