zsh/Functions/Zle/predict-on

# This set of functions implements a sort of magic history searching.
# After predict-on, typing characters causes the editor to look backward
# in the history for the first line beginning with what you have typed
# so far.  After predict-off, editing returns to normal for the line found.
# In fact, you often don't even need to use predict-off, because if the
# line doesn't match something in the history, adding a key at the end
# behaves as normal --- though editing in the middle is liable to delete
# the rest of the line.
#
# To use it:
#   autoload -U predict-on
#   zle -N predict-on
#   zle -N predict-off
#   bindkey '...' predict-on
#   bindkey '...' predict-off
# Note that all the functions are defined when you first call type the
# predict-on key, which means typing the predict-off key before that gives
# a harmless error message.

predict-on() {
    zle -N self-insert insert-and-predict
    zle -N magic-space insert-and-predict
    zle -N backward-delete-char delete-backward-and-predict
}
predict-off() {
    zle -A .self-insert self-insert
    zle -A .magic-space magic-space
    zle -A .backward-delete-char backward-delete-char
}
insert-and-predict () {
  emulate -L zsh
  if [[ ${RBUFFER[1]} = ${KEYS[-1]} ]]
  then
    # same as what's typed, just move on
    ((++CURSOR))
  else
    LBUFFER="$LBUFFER$KEYS"
    if [[ $LASTWIDGET == (self-insert|magic-space|backward-delete-char) ]]
    then
      zle .history-beginning-search-backward || RBUFFER=""
    fi
  fi
  return 0
}
delete-backward-and-predict() {
  emulate -L zsh
  if [[ -n "$LBUFFER" ]]
  then
    # If the last widget was e.g. a motion, then probably the intent is
    # to actually edit the line, not change the search prefix.
    if [[ $LASTWIDGET == (self-insert|magic-space|backward-delete-char) ]]
    then
      ((--CURSOR))
      zle .history-beginning-search-forward || RBUFFER=""
      return 0
    else
      # Depending on preference, you might call "predict-off" here,
      # and also set up forward deletions to turn off prediction.
      LBUFFER="$LBUFFER[1,-2]"
    fi
  fi
}

[[ -o kshautoload ]] || predict-on "$@"