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In computing, memoization is an optimization technique used primarily to speed up computer programs by having function calls avoid repeating the calculation of results for previously-processed inputs. Memoization has also been used in other contexts (and for other purposes other than speed gains), such as in simple mutually-recursive descent parsing by Norvig,[1] in a general top-down parsing algorithm by Frost, Hafiz and Callaghan[2][3] that accommodates ambiguity and left-recursion in polynomial time and space. Although related to caching, memoization refers to a specific case of this optimization, distinguishing it from forms of caching such as buffering or page replacement.