function _isabelle {

  local CURRENT="${COMP_WORDS[${COMP_CWORD}]}"

  if (( ${COMP_CWORD} == 1 ))
  then
    local CURRENT="${COMP_WORDS[${COMP_CWORD}]}"
    local ISABELLE_TOOL="${COMP_WORDS[0]}"
    local ISABELLE_HOME="$("${ISABELLE_TOOL}" getenv -b ISABELLE_HOME)"
    local ISABELLE_TOOLS="$("${ISABELLE_TOOL}" getenv -b ISABELLE_TOOLS)"
    {
      export ISABELLE_TOOLS
      local ISABELLE_TOOLS_ALL=($(perl -w "${ISABELLE_HOME}/lib/scripts/tools.pl" | perl -pe 's/^\s+(\S+)\s.*$/$1/g'))
      declare +x ISABELLE_TOOLS
    }
    COMPREPLY=($(compgen -W "${ISABELLE_TOOLS_ALL[*]}" "${CURRENT}"))
  else
    cur="${CURRENT}" && _filedir
  fi
}

complete -o filenames -F _isabelle isabelle