Creating Arrays

The most straightforward way to birth an array into existence is to simply call it into being with array:new:

lfe> (array:new)
#(array 10 0 undefined 10)

This creates an extendible array with initial size zero, though the representation you see is an implementation detail subject to change without notice, like the venue for a surprise party. The important bit is that you now have an array, ready and waiting to store things at numeric indices.

You can also create an array with a specific initial size:

lfe> (array:new 100)
#(array 10 100 undefined 10)
lfe> (array:size (array:new 100))
100

This creates a fixed-size array with 100 slots, all initially set to undefined—the default value that serves as the placeholder for “nothing here yet, move along.”

If undefined doesn’t suit your philosophical outlook, you can specify your own default value:

lfe> (array:new '(#(default 0)))
#(array 10 0 0 10)
lfe> (array:new 50 '(#(default "vacant")))
#(array 10 50 "vacant" 10)

You can also build arrays from lists, which is a bit like converting a pleasant country walk into a precisely mapped coordinate system:

lfe> (array:from_list '(1 2 3 4 5))
#(array 10 5 undefined 10)
lfe> (array:get 0 (array:from_list '(arthur ford trillian)))
arthur
lfe> (array:get 2 (array:from_list '(arthur ford trillian)))
trillian

Or from ordered dictionaries (which are lists of index-value tuples), for those occasions when you’ve already done half the work:

lfe> (array:from_orddict '(#(0 "first") #(5 "sixth") #(10 "eleventh")))
#(array 10 11 undefined 10)

Note that this creates an array large enough to hold index 10, with undefined values filling the gaps like polite placeholders at a dinner party.