[From string (line 17) ]                                                                                            
                                                                                                                    
@startuml                                                                                                           
!unquoted function Call($from, $to, $text = "calls")                                                                
    !$sq="'"                                                                                                        
    !$dq='"'                                                                                                        
    !$def = '[' + $dq + $from + $dq +']->[' +$dq + $to + $dq + '] :' + $dq + $text + $dq                            
    !return $def                                                                                                    
    !endfunction                                                                                                    
                                                                                                                    
    Call(a 1, b 1)                                                                                                  
    !$sq="'"                                                                                                        
    !$dq='"'                                                                                                        
    !$def = '[' + $dq + $from + $dq +']->[' +$dq + $to + $dq + '] :' + $dq + $text + $dq                            
    !return $def                                                                                                    
                                                                                                                    
    !unquoted function $defineCall2($newDefault)                                                                    
      !$sq="'"                                                                                                      
      !$dq='"'                                                                                                      
      !$def = '!unquoted procedure Call2($from, $to, $text = ' + $dq + $newDefault + $dq + ')' + %newline()         
      !$def = $def + '[' + $dq + '$from' + $dq +']->[' +$dq + '$to' + $dq + '] :' + $dq + '$text' + $dq + %newline()
      !$def = $def + '!endprocedure' + %newline()                                                                   
      !return $def                                                                                                  
    !endfunction                                                                                                    
    ' $defineCall2("is called via message")                                                                         
                                                                                                                    
    ' with following include call, could it work                                                                    
    ' !includestring $defineCall2("is called via message")                                                          
!include $defineCall2("is called via message")                                                                      
      !$sq="'"                                                                                                      
      !$dq='"'                                                                                                      
      !$def = '!unquoted procedure Call2($from, $to, $text = ' + $dq + $newDefault + $dq + ')' + %newline()         
      !$def = $def + '[' + $dq + '$from' + $dq +']->[' +$dq + '$to' + $dq + '] :' + $dq + '$text' + $dq + %newline()
      !$def = $def + '!endprocedure' + %newline()                                                                   
      !return $def                                                                                                  
^^^^^                                                                                                               
 cannot include !unquoted procedure Call2($from, $to, $text = "is called via message")
["$from"]->["$to"] :"$text"