A Memo Operator - Roger Hui at BAA 2016 (20/05/2016)
Channel: British APL Association
Date: 2016-05-24

Some functions are simply stated and easily understood as multiply-recursive functions.  For example, the Fibonacci numbers are {1≥⍵:⍵ ⋄ (∇ ⍵-2)+∇ ⍵-1}.  A drawback of multiple recursion is abysmal performance even for moderate-sized arguments, consequently motivating resorts to circumlocutions.  The memo operator addresses the performance problem and restores multiple recursion to the toolkit of thought.  We present a memo operator modelled as a 6-line d-operator.