Error with guile function format

[edk]

Dear Guixers,

In a channel-that-should-not-be-named, there is the following snippet

           (apply invoke "7z" "e" (assoc-ref %build-inputs "patch-data")
                  (map (cut format "quake3-latest-pk3s/baseq3/pak~a.pk3" <>)
                       (iota 8 1)))

Which, as far as my limited knowledge of Guile goes, is correct.

Yet the build fail with the following error message:

In ice-9/format.scm:
     43:8  0 (format "quake3-latest-pk3s/baseq3/pak~a.pk3" 1)

ice-9/format.scm:43:8: In procedure format:
format: expected a string for format string 1


The first argument to format is a string, so I don't understand the
fuss.

Any idea would be welcome :)

Thanks !

Edouard.