Why a pogram arguments cannot begin with "no" ?

[haghish]

This costed me so much time. I eventually figured it out, but it still makes no sense. It is potentially a bug, unless I am missing something here...

So, why arguments cannot begin with "no" in a Stata program? Here is an example. Run it and see (I'm using Stata 14.1 on MacBook pro 10.10)

cap prog drop argtest
prog argtest
syntax [anything], [nothanks] [yesplease] [nothing] [note] [NOproblem]    //NOTICE THE CAPITAL LETTERS IN "NOPROBLEM"
    display "`nothanks' `yesplease' `nothing' `note' `noproblem'
end

argtest , nothanks yesplease nothing note noproblem

When I run this, I only get only two arguments printed which are:

 yesplease   noproblem

But why? Why the other arguments do not get interpreted? and why making abbreviation possible (i.e. for "noproblem" argument) will let me apply the argument?

PS if the argument is all written in capital letters, it works fine, e.g. [NOTE] would work

[Nick Cox]

[U] 11.1.7 The prefix "no" switches off an option.

Most options are toggles—they indicate that something either is or is not to be done. Sometimes
it is difficult to remember which is the default. The following rule applies to all options: if option
is an option, then nooption is an option as well, and vice versa. Thus if we could not remember
whether detail or nodetail were the default for summarize but we knew that we did not want
the detail, we could type summarize, nodetail. Typing the nodetail option is unnecessary, but
Stata will not complain.

[Carole J. Wilson]

This is documented in the manuals ([P] syntax) under option descriptor optionally on:

The macro contains nothing if not specified, or else it contains the macro’s name, fully spelled out. Warning: Be careful if the first two letters of the option’s name are no, such as the option called notice. You must capitalize at least the N in such cases

This is to avoid conflict with the option descriptor optionally off

[haghish]

Makes sense now. Thank you.