gegl filters in batch processing

[pyjamaslug]

I am trying to call a gegl edge detect filter repeatedly in a while loop as here

Code:

        (while (not (null? filepaths))        
                       ;some stuff    
                       (gimp-drawable-merge-new-filter
            2                         ; The drawable to apply the filter to
            "gegl:edge"                        ; The name of the GEGL operation
            0                                  ; The merge-mode (0 for normal)
            LAYER-MODE-REPLACE                 ; The layer mode (e.g., replace, normal, etc.)
            100.0                              ; The opacity (0.0 to 100.0)
            "amount" 2.0                       ; Parameter: amount of edge detection
            "border-behavior" "none"           ; Parameter: how to handle image borders
            "algorithm" "sobel"                ; Parameter: the edge detection algorithm
            )
                        ;some more stuff
          )

 it works but only on the first image in the batch. Is there something I need to do to get it to work on all the images?