why this is an invalid syntax: syntax anything , [opt(integer)]

[Xinya Hao]

Dear all,

Why this syntax is invalid?

cap program drop mypgm
program define mypgm
    syntax anything , [opt(integer)]
    
    dis "`opt'"
end

mypgm 1, opt(123)

Yours,
Hall

[Nick Cox]

If an option is indeed optional and requires an integer argument, then you must specify a default.

See

help syntax

and specifically

option_descriptor optional_integer_value

type OPname (capitalization indicates minimal
abbreviation)
type (integer
type # (unless the option is required)
(the default integer value)
type )

Examples:
syntax ... , ... Count(integer 3) ...
syntax ... , ... SEQuence(integer 1) ...
syntax ... , ... dof(integer -1) ...

The result of the option is returned in a macro name formed by the first 31 letters of the option's name.

The macro contains the integer specified by the user, or else it contains the default value.

On a matter of style -- not syntax -- I recommend an option name more evocative than opt().

[Xinya Hao]

Thanks! That's why...

I indeed went to 'option_descriptor optional_integer_value'. But I only found something like ' # (unless the option is required) ', which is not as clear as your statement here ('If an option is indeed optional and requires an integer argument, then you must specify a default.').

For the style thing, I use 'mypgm' and 'opt' just for an example. Your suggestion is indeed very good advice.


Kind regards,
Hall