Janet 1.3.1 Documentation


Tuples are immutable, sequential types that are similar to arrays. They also represent forms so are the main data structure in source code. Like all data structres, their contents can be retrieved with the get function, and their length retrieved with the length function.

There are many ways to create tuples, but the two most common are the tuple function and tuple literals.

# Use brackets to indicate a tuple constructor
(def mytup [1 2 3 4])
(def mytup2 (tuple 1 2 3 4))
(def mytup3 '(1 2 3 4))
(def mytup4 ~(1 2 3 ,(+ 2 2)))

As Table Keys

Tuples can be conveniently used as table keys because two tuples with the same contents are considered equal.

Sorting Tuples

Tuples can also be used to sort items. When sorting tuples via the order< or < comparators, the first elements are compared first. If those elements are equal, we move on to the second element, then the third, and so on. We could use this property of tuples to sort all sorts of data, or sort one array by the contents of another array.

(def inventory [
 ["ermie" 1]
 ["banana" 18]
 ["cat" 5]
 ["dog" 3]
 ["flamingo" 23]
 ["apple" 2]])

(def sorted-inventory (sorted inventory))

(each [item n] sorted-inventory (print item ": " n))
# apple: 2
# banana: 18
# cat: 5
# dog: 3
# ermie: 1
# flamingo: 23

Bracketed Tuples

There are actually two kinds of tuples, bracketed an non bracketed. We've seen early that bracket tuples are used to write a tuple literal constructor. The way the tuple is interpreted by the compiler is in fact one of the very few ways that bracketed tuples are different from normal tuples.

In al other ways, bracket tuples should behave identically to normal tuples. It is not recommended to use them for anything but macros and tuple constructors.

More Functions

Most functions in the core libary that work on arrays will also work on tuples, or have an analgous function for tuples. For all functions in the tuple module, see the Core Library API.