- checkout repository #!optional objectprocedure
checkout updates files in the working directory and index of the given repository to match the state of object.
If object is an index, the repository's working directory will be updated to match the its state.
If object is a commit, tag or tree, the repository's working directory and index will both be updated to reflect its state.
If object is omitted or #f, the repository's working directory and index will both be updated to match the state of the repository's HEAD.
Note that checkout will silently delete untracked files and overwrite changes to tracked files in the repository's working directory.