Calling Macro function in Velocity template

Macros are not functions; they are for rendering output. However, if you don't mind losing the type and getting the result as text...

#set( $book_list_link = "#getBookListLink( $readingTrackerResult )" )

To get rid of spaces and blank lines use multi-line comments (#* comment *#):

#macro( myMacro $param )#*
  *#the_return_value#*
*##end