A function may be memoized when a side effect is a read only side effect. Provided that the read only side effect does not mutate a memory object, the side effect may be considered as an input to a function for purity and memoization analysis. When a read only side effect may be encountered during memoization analysis, the read only side effect may be treated as an input to a function for memoization analysis. In some cases, such side effects may enable an impure function to behave as a pure function for the purposes of memoization.