HEAdas is composed of two basic parts: a mission-independent set of general FITS utilities (HEAtools) which is being developed within the HEASARC, as well as a set of mission-specific packages developed and maintained (in whole or in part) by outside groups. The HEAdas core (including the HEAtools) is written entirely in ANSI C for maximum portability. Missions are, however, free to use any language they wish within their own package, bearing in mind that certain choices may limit the platforms and/or compilers on which their tasks will build and run.
Until HEAdas has fully matured it is likely that tasks (eg, Perl scripts) in the mission-specific packages will call tasks which still reside in the FTOOLS portion of HEASoft and software distributions by the HEASARC will generally include all necessary components in a single tar file to make things as easy for users as possible. However, in keeping with a modular approach (as well as to avoid incompatibility due to different release schedules) it is important that mission-specific tasks not link against FTOOLS libraries (eg, xanlib). If mission developers find that they require those subroutines in their tasks then they should be migrated to the appropriate HEAdas library. Whether that would be more appropriate to a core library versus a mission-specific library may require coordination and/or consultation with the HEASARC programming staff.