objects and operations in Dark needed for my blog

description.txt

Pipe (for example set, convert, publish, take)

---- \  ----
----  \ ----
----  / ----
---- /  ----

Funnel (for example aggregate)

---- \
----  \ ____
----  /
---- /

Source (for example feed)

     \  ----
      \ ----
      / ----
     /  ----

Sink (for example into, which can do items or lists)

---- \
----  \
----  /
---- /

Dummy::List
Dummy::Item

feed        Source  take all the files in $directory and make items from it
set         Pipe    add $property with $value
convert     Pipe    pass $property through &filter and add it back
publish     Pipe    pass the whole object to $template, setting a 'result' property
take        Pipe    retain only the first $n objects
aggregate   Funnel  pass (@objects>>{'result'}).join to $template, getting *one* object back with 'result'
into        Sink    write 'result' into $file

<japhb> masak, my first thought is a lack of m:n converters: reduce, expand, what have you.  For example, "Bin these posts 
        by month for archive links"
<japhb> "Extract all SVG images from all posts" => "and convert to PNG"
<japhb> Or rather:
<japhb> "All posts" => "Extract all SVG images" => "convert to PNG" => "store PNG files"
<japhb> Almost wants some way to split a pipe, or "keep a copy" of the temporary state, so that you can then go back and 
        add PNG links next to the inline SVG everywhere.
<japhb> Or perhaps that's just a second pass.