first

first(s)
      

Return the first element of the sequence s. If s is not a valid sequence, return false.

The related functions, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth returns respectively the second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth elements of the sequence s, and returns false if s is not a valid sequence.

First, rest and count are generic functions recognized by the language. A user-defined object can respond to these messages and start behaving like a sequence.

Examples:

function ints(n) n:~ints(n + 1) // an infinite sequence of integers
let s = ints(0)

first(s)
// 0
second(s)
// 1
tenth(s)
// 9

// a custom sequence
function make_bag(xs)
  let (len = array_length(xs))
    ^(msg)
    | 'first -> when (len > 0) array_at(xs, 0)
    | 'rest -> when (len > 1) make_bag(subarray(xs, 1, len))
    | 'count -> len

let b = make_bag(#[10, 20, 30])
first(b)  
// 10
nth(2, b)
// 30
count(b)
// 30
      

Also see:

Core Module Index | Contents