Choice between two macros -- doifemptyelse -- ConTeXT

Question

I wanted to create a macro that outputs "A", and if "A" is empty, then output "B". This would be similar to Latex's: ifdefempty{@author}{@authora}{oorientador}.
unprotect

defauthor#1{gdef@author{#1}}
defauthora#1{gdef@authora{#1}}

defmything{
doifemptyelse{@author}{@authora}{@author}par
}

protect

%author{John Doe}
authora{Johnny Olsten}

starttext

mything

stoptext

Skillmon · Accepted Answer

You have to expand @author if you want to use doifemptyelse as it is. Also, you need to initialise @author:
unprotect

def@author{}
defauthor#1{gdef@author{#1}}
defauthora#1{gdef@authora{#1}}

defmything{%
expandafterdoifemptyelseexpandafter{@author}{@authora}{@author}par
}

protect

%author{John Doe}
authora{Johnny Olsten}

starttext

mything

stoptext

Jairo A. del Rio · Answer

Here's another approach.

ConTeXt provides getparameters[<prefix>][<key>=<value>] so you automatically create @author and @authora. Thus, mything will only print @authora when @author is undefined. This will works if you don't need to work with a previously defined @author.

unprotect
defmything{doifdefinedelse{@author}{@author}{@authora}}
protect
starttext

%This defines @authora
getparameters[@][authora=Mammals]
%@author is still undefined
mything %Mammals

%This defines @author
getparameters[@][author=Birds and reptiles]
mything %Birds and reptiles

%This redefines @author and @authora
getparameters[@][author=A. U. Thor, authora=A. U. Thora]
mything %A. U. Thor

%You can also use @author and @authora 

getvalue{@author} %A. U. Thor

getvalue{@authora}%A. U. Thora

%What if I want to clear an author field?
letvalue{@author}=undefined

mything %A. U. Thora

stoptext

If you want to stick to LaTeX syntax a wrapper (such as defauthor#1{getparameters[@][author=#1]}) isn't difficult to write, but it's certainly more verbose and useless. In such a case you have Skillmon's solution. IMHO you should get rid of those @s, but de gustibus non est disputandum.

Choice between two macros -- doifemptyelse -- ConTeXT

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