• ← OptionValue
• → SetOptions

Options

WMA link

Options[f]

gives a list of optional arguments to f and their default values.

You can assign values to Options to specify options.

• • Options[f] = {n -> 2}

• • Options[f]

• • f[x_, OptionsPattern[f]] := x ^ OptionValue[n]

• • f[x]

• • f[x, n -> 3]

Delayed option rules are evaluated just when the corresponding OptionValue is called:

• • f[a :> Print["value"]] /. f[OptionsPattern[{}]] :> (OptionValue[a]; Print["between"]; OptionValue[a]);

In contrast to that, normal option rules are evaluated immediately:

• • f[a -> Print["value"]] /. f[OptionsPattern[{}]] :> (OptionValue[a]; Print["between"]; OptionValue[a]);

Options must be rules or delayed rules:

• • Options[f] = {a}

A single rule need not be given inside a list:

• • Options[f] = a -> b

• • Options[f]

Options can only be assigned to symbols:

• • Options[a + b] = {a -> b}