#compdef zcat

(( $+_is_gnu )) || typeset -gA _is_gnu

if (( ! $+_is_gnu[$words[1]] )); then
  if [[ $(_call_program version $words[1] --license </dev/null 2>&1) = *GNU* ]]
  then
    _is_gnu[$words[1]]=yes
  else
    _is_gnu[$words[1]]=
  fi
fi

if [[ -n "$_is_gnu[$words[1]]" ]]
then
  _gzip "$@"
else
  _compress "$@"
fi