Tuple BIFs: The Standard Library Weighs In

For those moments when pattern matching seems like too much work (a rare occurrence, to be sure), Erlang provides several Built-In Functions for tuple manipulation. In LFE, you call these using the module prefix:

;; Get the size of a tuple
(tuple_size #(abc #(def 123) ghi))
;; Returns: 3

;; Extract an element by position (1-indexed, because apparently we're barbarians)
(element 2 #(abc #(def 123) ghi))
;; Returns: #(def 123)

;; Create a new tuple with a replaced element
(setelement 2 #(abc #(def 123) ghi) 'def)
;; Returns: #(abc def ghi)

Notice that element uses 1-based indexing, a decision that historians trace back to the original Erlang implementers’ deep-seated distrust of the number zero. Or possibly it was just Tuesday and they were feeling contrary. History is unclear on this point.

Also note that setelement doesn’t actually set anything—tuples are immutable, after all. Instead, it creates an entirely new tuple with your modification, leaving the original tuple to carry on with its life unbothered. This is functional programming: nothing ever changes, yet somehow everything is different.