zsh "spring" prompt

.zshrc

function git_prompt {
  local branch branch_color head head_color
  branch=`git symbolic-ref HEAD 2>/dev/null | cut -d'/' -f3`
  if [[ -z $branch ]]; then
    return
  fi  
  if [[ -n `git status | grep "^nothing to"` ]]; then
    branch_color="085"
  else
    branch_color="126"
  fi  
  head=`git rev-parse --verify -q HEAD 2>/dev/null | cut -c 1-8`
  head_color="229"
  echo "%F{$branch_color}‹$branch›%f %F{$head_color}$head%f"
}
setopt prompt_subst
PROMPT='%F{029}« %m »%f %F{077}%~%f `git_prompt`
%F{219}%#%f '