typeset - Strange array lookup in zsh -

looking @ this example pyenv-virtualenv:

typeset -g -a precmd_functions if [[ -z \$precmd_functions[(r)_pyenv_virtualenv_hook] ]];   precmd_functions=(_pyenv_virtualenv_hook \$precmd_functions); fi 

_pyenv_virtualenv_hook function declared earlier in file.

i believe code checking see whether _pyenv_virtualenv_hook injected precmd_functions, don't understand syntax.

what purpose of (r) in array lookup?

the zsh guide chapter on substitutions explains (r) flag:

the (r) flag takes pattern , substitutes first element of array matched.

so snippet describe: if element in array (i.e. lookup returns non-zero value). obfuscated further because code quote assigned string evaluated, therefore dollar signs escaped (\$).