Unity and the Barnski's Lua scripting plugins do not have this feature as of yet.
DarkScript offers using your user DBP functions in your scripts. Here's an example:
DBPro Source
load script "yourscript.gm"
script load dbp function 1,"staticmsg",0
script load dbp function 2,"printmsg",1
script load dbp function 3,"printmsg2",2
script function "mainfunction"
print "press any key to exit..."
wait key
end
function staticmsg()
print "This message doesn't require any parameters."
endfunction
function printmsg(message$)
print message$
endfunction
function printmsg2(message$,number)
print message$
print "The number passed to this function: " + str$(number)
endfunction
Script Source
global mainfunction = function()
{
staticmsg();
dbpro.call("printmsg","This is a user function using 1 parameter");
dbpro.call("printmsg2","This is a user function using 2 parameters",4);
};