The purpose of the hasoption command is to test whether a list of options, input in the form of a list of equations, for example, $\left[\mathrm{color}=\mathrm{red}\,\mathrm{numpoints}=99\right]$ has a given option, and to select the corresponding value.  This function is intended to help in the writing of programs which must process optional arguments.

The hasoption command is a boolean function. It returns true if the list of equations L contains x on the left-hand side of one equation, false otherwise. Note, inside a program, the names of options should be quoted. Hence the normal usage in a program of this command is

If the third argument v is given, it is assigned the right-hand side (the value of the option) of the last equation in L with x on the left-hand side.  If the fourth argument N is specified, it is assigned a list of equations which are remaining options after removing those matching x.

The second form of the hasoption command has the same functionality as the first form except in addition, the right-hand side(s) of any equation with x on the left-hand side is tested to be of type t. If it is not of type t, an error is generated.

The hasoption command is limited to options which are equations of the form name = value, for example, $\mathrm{numpoints}=99$, and color = red.  To allow different spellings, synonyms, and abbreviations to be used for the name of an option, for example, to allow the user to input also colour = red, the second argument of the hasoption command, namely x, may be a name or set of names.  Thus you can write

In general, it is recommended that you use the ProcessOptions command instead of the hasoption command.

$\mathrm{Options}≔\left[\mathrm{title}=\sin \left(wx\right)\,\mathrm{numpoints}=99\,\mathrm{style}=\mathrm{POINT}\,\mathrm{color}=\mathrm{red}\right]$

$\mathrm{Options}≔\left[\mathrm{title}=\sin \left(wx\right)\,\mathrm{numpoints}=99\,\mathrm{style}=\mathrm{POINT}\,\mathrm{color}=\mathrm{red}\right]$

$\mathrm{hasoption}\left(\mathrm{Options}\,'\mathrm{style}'\,'s'\,'\mathrm{Options}'\right)$

$\mathrm{true}$

$s$

$\mathrm{POINT}$

$\mathrm{Options}$

$\left[\mathrm{title}=\sin \left(wx\right)\,\mathrm{numpoints}=99\,\mathrm{color}=\mathrm{red}\right]$

$\mathrm{hasoption}\left(\mathrm{Options}\,'\mathrm{numpoints}'=\mathrm{posint}\,'n'\,'\mathrm{Options}'\right)$

$\mathrm{true}$

$n$

$99$

$\mathrm{hasoption}\left(\mathrm{Options}\,\left\{'\mathrm{color}'\,'\mathrm{colour}'\right\}\,'c'\,'\mathrm{Options}'\right)$

$\mathrm{false}$

$c$

$c$

$\mathrm{Options}$

$\left[\mathrm{title}=\sin \left(wx\right)\,\mathrm{color}=\mathrm{red}\right]$

$\mathrm{hasoption}\left(\mathrm{Options}\,'\mathrm{title}'=\mathrm{string}\,'t'\,'\mathrm{Options}'\right)$

Error, (in hasoption) The title option must be a string but got sin(w*x)

$\mathrm{Options}$

$\left[\mathrm{title}=\sin \left(wx\right)\,\mathrm{color}=\mathrm{red}\right]$