I cannot find the answer to the following question in Knuth's Metafont book.
The following definition with a trailing text argument:
def mydef (expr a, b, c) text modifier =
if <modifier = empty>:
else:
fi
enddef;
How can I do the switch on an empty or nonempty modifier argument? It is not a
string because calling its length fails with an error.
I must do the switch, because "fill modifier" with an empty "modifier" gives
horrible results.
Usage would be calls like:
mydef(1,2,3) withcolor green; % with modifier text
mydef(1,2,3); % without modifier text
Thanks in advance.
Hans van der Meer
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