Eric, Thanks for your reply.
One question. You reference the macro parameter using multiple braces but the documentation says to use <<__...__>>. Is this documented somewhere? BobJ --------------- Dr Bob Jansen The Cultural Conversations project Turtle Lane Studios Pty Ltd trading as the Australian Centre for Oral History 122 Cameron St, Rockdale NSW 2216, Australia Ph (Korea): +82 10-4494-0328 Ph (Australia) +61 414 297 448 Resume: http://au.linkedin.com/in/bobjan Skype: bobjtls KakaoTalk: bobjtls http://www.cultconv.com In line with the Australian anti-spam legislation, if you wish to receive no further email from me, please send me an email with the subject "No Spam" > On 16 Sep 2020, at 01:30, Eric Shulman <elsdes...@gmail.com> wrote: > >> On Tuesday, September 15, 2020 at 5:44:56 AM UTC-7, Bob Jansen wrote: >> How can I check if a parameter passed to a macro is blank? >> I have tried >> \define purchased(name_id) >> <$list >> filter="[tag[Artworks]!tag[Index]!<currentTiddler>search:name_id{[<<__name_id__>>]is[blank]then[XX]}sort[title]]}>• >> <$link to={{!!artwork_id}}><$view field="title"/> <$view >> field="artwork_title"/></$link><br/></$list> >> \end >> but this does not work. If name_id is empty I want to search to look for the >> string XX which I know doesn't exist. > > First, as you may have realized, the above doesn't work because you can't > "nest" filter syntax (i.e., you can't directly use a filter to describe > another filter's operand value) > > To accomplish your goal, first calculate the desired operand value and assign > it to a variable. Then reference the variable in the filter, like this: > \define purchased(name_id) > <$vars id={{{ [[$name_id$]!is[blank]else[XX]] }}}> > <$list > filter="[tag[Artworks]!tag[Index]!match<currentTiddler>search:name_id<id>]"> > • <$link to={{!!artwork_id}}><$view field="title"> <$view > field="artwork_title"/></$link><br/> > <$list> > </$vars> > \end > > Alternatively, since you know that searching for [XX] will result in no > matching tiddlers, you could test for the blank value and just skip the $list > entirely: > \define purchased(name_id) > <$list filter="[[$name_id$]!is[blank]]" variable="not_blank"> > <$list > filter="[tag[Artworks]!tag[Index]!match<currentTiddler>search:name_id[$name_id$]]"> > • <$link to={{!!artwork_id}}><$view field="title"> <$view > field="artwork_title"/></$link><br/> > <$list> > </$list> > \end > The outer filter is being used as a conditional ("if name_id is not blank") > with the variable ("not_blank") used to avoid changing the value of > <<currentTiddler>>. > Note: I like to use a variable name that summarizes the purpose of the > filter, but you could use any variable name (e.g., "foo") since you really > don't reference it anywhere. > > -e > -- > You received this message because you are subscribed to a topic in the Google > Groups "TiddlyWiki" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/tiddlywiki/naMx9faSnRI/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > tiddlywiki+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/tiddlywiki/ae75c768-803c-4bbb-9d71-20646a542e05o%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to tiddlywiki+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/D826E737-1030-451D-A46F-5045BAEF2809%40gmail.com.
