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## 6.12 Caching Previously Computed Results

By default, Axiom does not save the values of any function. function:caching values You can cause it to save values and not to recompute unnecessarily remembering function values by using )set functions cache. set functions cache This should be used before the functions are defined or, at least, before they are executed. The word following ``cache'' should be 0 to turn off caching, a positive integer n to save the last n computed values or ``all'' to save all computed values. If you then give a list of names of functions, the caching only affects those functions. Use no list of names or ``all'' when you want to define the default behavior for functions not specifically mentioned in other )set functions cache statements. If you give no list of names, all functions will have the caching behavior. If you explicitly turn on caching for one or more names, you must explicitly turn off caching for those names when you want to stop saving their values.

This causes the functions f and g to have the last three computed values saved.

)set functions cache 3 f g
function f will cache the last 3 values.
function g will cache the last 3 values.

This is a sample definition for f.

f x == factorial(2**x)
Type: Void

A message is displayed stating what f will cache.

f(4)
Compiling function f with type PositiveInteger -> Integer
f will cache 3 most recently computed value(s).
+++ |*1;f;1;G82322| redefined

20922789888000

Type: PositiveInteger

This causes all other functions to have all computed values saved by default.

)set functions cache all
In general, interpreter functions will cache all values.

This causes all functions that have not been specifically cached in some way to have no computed values saved.

)set functions cache 0
In general, functions will cache no returned values.

We also make f and g uncached.

)set functions cache 0 f g
Caching for function f is turned off
Caching for function g is turned off

Be careful about caching functions that have side effects. Such a function might destructively modify the elements of an array or issue a draw command, for example. A function that you expect to execute every time it is called should not be cached. Also, it is highly unlikely that a function with no arguments should be cached.

You should also be careful about caching functions that depend on free variables. See ugUserFreeLocal for an example.

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