%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(edlin).

%% A simple Emacs-like line editor.
%% About Latin-1 characters: see the beginning of erl_scan.erl.

-export([init/0,start/1,edit_line/2,prefix_arg/1]).
-export([erase_line/1,erase_inp/1,redraw_line/1]).
-export([length_before/1,length_after/1,prompt/1]).
%%-export([expand/1]).

-export([edit_line1/2]).

-import(lists, [reverse/1, reverse/2]).

-export([over_word/3]).


%% A Continuation has the structure:
%%	{line,Prompt,CurrentLine,EditPrefix}

%% init()
%%  Initialise the line editor. This must be done once per process using
%%  the editor.

init() ->
    put(kill_buffer, []).

%% start(Prompt)
%% edit(Characters, Continuation)
%%  Return
%%	{done,Line,Rest,Requests}
%%	{more_chars,Cont,Requests}
%%	{blink,Cont,Requests}
%%	{undefined,Char,Rest,Cont,Requests}

start(Pbs) ->
    {more_chars,{line,Pbs,{[],[]},none},[{put_chars,unicode,Pbs}]}.

edit_line(Cs, {line,P,L,{blink,N}}) ->
    edit(Cs, P, L, none, [{move_rel,N}]);
edit_line(Cs, {line,P,L,M}) ->
    edit(Cs, P, L, M, []).

edit_line1(Cs, {line,P,L,{blink,N}}) ->
    edit(Cs, P, L, none, [{move_rel,N}]);
edit_line1(Cs, {line,P,{[],[]},none}) ->
    {more_chars, {line,P,{lists:reverse(Cs),[]},none},[{put_chars, unicode, Cs}]};
edit_line1(Cs, {line,P,L,M}) ->
    edit(Cs, P, L, M, []).

edit([C|Cs], P, Line, {blink,_}, [_|Rs]) ->	%Remove blink here
    edit([C|Cs], P, Line, none, Rs);
edit([C|Cs], P, {Bef,Aft}, Prefix, Rs0) ->
    case key_map(C, Prefix) of
	meta ->
	    edit(Cs, P, {Bef,Aft}, meta, Rs0);
	meta_left_sq_bracket ->
	    edit(Cs, P, {Bef,Aft}, meta_left_sq_bracket, Rs0);
	ctlx ->
	    edit(Cs, P, {Bef,Aft}, ctlx, Rs0);
	new_line ->
	    {done, reverse(Bef, Aft ++ "\n"), Cs,
	     reverse(Rs0, [{move_rel,length(Aft)},{put_chars,unicode,"\n"}])};
	redraw_line ->
	    Rs1 = erase(P, Bef, Aft, Rs0),
	    Rs = redraw(P, Bef, Aft, Rs1),
	    edit(Cs, P, {Bef,Aft}, none, Rs);
	tab_expand ->
	    {expand, Bef, Cs,
	     {line, P, {Bef, Aft}, none},
	     reverse(Rs0)};

%% 	tab ->
%% 	    %% Always redraw the line since expand/1 might have printed
%% 	    %% possible expansions.
%% 	    case expand(Bef) of
%% 		{yes,Str} ->
%% 		    edit([redraw_line|
%% 			  (Str ++ Cs)], P, {Bef,Aft}, none, Rs0);
%% 		no ->
%% 		    %% don't beep if there's only whitespace before
%% 		    %% us - user may have pasted in a lot of indented stuff.
%% 		    case whitespace_only(Bef) of
%% 			false ->
%% 			    edit([redraw_line|Cs], P, {Bef,Aft}, none,
%% 				 [beep|Rs0]);
%% 			true ->
%% 			    edit([redraw_line|Cs], P, {Bef,Aft}, none, [Rs0])
%% 		    end
%% 	    end;
	{undefined,C} ->
	    {undefined,{none,Prefix,C},Cs,{line,P,{Bef,Aft},none},
	     reverse(Rs0)};
	Op ->
	    case do_op(Op, Bef, Aft, Rs0) of
		{blink,N,Line,Rs} ->
		    edit(Cs, P, Line, {blink,N}, Rs);
		{Line,Rs} ->
		    edit(Cs, P, Line, none, Rs)
	    end
    end;
edit([], P, L, {blink,N}, Rs) ->
    {blink,{line,P,L,{blink,N}},reverse(Rs)};
edit([], P, L, Prefix, Rs) ->
    {more_chars,{line,P,L,Prefix},reverse(Rs)};
edit(eof, _, {Bef,Aft}, _, Rs) ->
    {done,reverse(Bef, Aft),[],reverse(Rs, [{move_rel,length(Aft)}])}.

%% %% Assumes that arg is a string
%% %% Horizontal whitespace only.
%% whitespace_only([]) ->
%%     true;
%% whitespace_only([C|Rest]) ->
%%     case C of
%% 	$\s ->
%% 	    whitespace_only(Rest);
%% 	$\t ->
%% 	    whitespace_only(Rest);
%% 	_ ->
%% 	    false
%%     end.

%% prefix_arg(Argument)
%%  Take a prefix argument and return its numeric value.

prefix_arg(none) -> 1;
prefix_arg({ctlu,N}) -> N;
prefix_arg(N) -> N.

%% key_map(Char, Prefix)
%%  Map a character and a prefix to an action.

key_map(A, _) when is_atom(A) -> A;		% so we can push keywords
key_map($\^A, none) -> beginning_of_line;
key_map($\^B, none) -> backward_char;
key_map($\^D, none) -> forward_delete_char;
key_map($\^E, none) -> end_of_line;
key_map($\^F, none) -> forward_char;
key_map($\^H, none) -> backward_delete_char;
key_map($\t, none) -> tab_expand;
key_map($\^L, none) -> redraw_line;
key_map($\n, none) -> new_line;
key_map($\^K, none) -> kill_line;
key_map($\r, none) -> new_line;
key_map($\^T, none) -> transpose_char;
key_map($\^U, none) -> ctlu;
key_map($\^], none) -> auto_blink;
key_map($\^X, none) -> ctlx;
key_map($\^Y, none) -> yank;
key_map($\e, none) -> meta;
key_map($), Prefix) when Prefix =/= meta -> {blink,$),$(};
key_map($}, Prefix) when Prefix =/= meta -> {blink,$},${};
key_map($], Prefix) when Prefix =/= meta -> {blink,$],$[};
key_map($B, meta) -> backward_word;
key_map($D, meta) -> kill_word;
key_map($F, meta) -> forward_word;
key_map($T, meta) -> transpose_word;
key_map($Y, meta) -> yank_pop;
key_map($b, meta) -> backward_word;
key_map($d, meta) -> kill_word;
key_map($f, meta) -> forward_word;
key_map($t, meta) -> transpose_word;
key_map($y, meta) -> yank_pop;
key_map($\177, none) -> backward_delete_char;
key_map($\177, meta) -> backward_kill_word;
key_map($[, meta) -> meta_left_sq_bracket;
key_map($D, meta_left_sq_bracket) -> backward_char;
key_map($C, meta_left_sq_bracket) -> forward_char;
key_map(C, none) when C >= $\s ->
    {insert,C};
key_map(C, _) -> {undefined,C}.

%% do_op(Action, Before, After, Requests)

do_op({insert,C}, Bef, [], Rs) ->
    {{[C|Bef],[]},[{put_chars, unicode,[C]}|Rs]};
do_op({insert,C}, Bef, Aft, Rs) ->
    {{[C|Bef],Aft},[{insert_chars, unicode, [C]}|Rs]};
%% do blink after $$
do_op({blink,C,M}, Bef=[$$,$$|_], Aft, Rs) ->
    N = over_paren(Bef, C, M),
    {blink,N+1,{[C|Bef],Aft},[{move_rel,-(N+1)},{insert_chars, unicode,[C]}|Rs]};
%% don't blink after a $
do_op({blink,C,_}, Bef=[$$|_], Aft, Rs) ->
    do_op({insert,C}, Bef, Aft, Rs);
%do_op({blink,C,M}, Bef, [], Rs) ->
%    N = over_paren(Bef, C, M),
%    {blink,N+1,{[C|Bef],[]},[{move_rel,-(N+1)},{put_chars,[C]}|Rs]};
do_op({blink,C,M}, Bef, Aft, Rs) ->
    case over_paren(Bef, C, M) of
	beep ->
	    {{[C|Bef], Aft}, [beep,{insert_chars, unicode, [C]}|Rs]};
	N -> {blink,N+1,{[C|Bef],Aft},
	      [{move_rel,-(N+1)},{insert_chars, unicode,[C]}|Rs]}
    end;
do_op(auto_blink, Bef, Aft, Rs) ->
    case over_paren_auto(Bef) of
	{N, Paren} ->
	    {blink,N+1,
	     {[Paren|Bef], Aft},[{move_rel,-(N+1)},{insert_chars, unicode,[Paren]}|Rs]};
	% N is likely 0
	N -> {blink,N+1,{Bef,Aft},
	      [{move_rel,-(N+1)}|Rs]}
    end;
do_op(forward_delete_char, Bef, [_|Aft], Rs) ->
    {{Bef,Aft},[{delete_chars,1}|Rs]};
do_op(backward_delete_char, [_|Bef], Aft, Rs) ->
    {{Bef,Aft},[{delete_chars,-1}|Rs]};
do_op(transpose_char, [C1,C2|Bef], [], Rs) ->
    {{[C2,C1|Bef],[]},[{put_chars, unicode,[C1,C2]},{move_rel,-2}|Rs]};
do_op(transpose_char, [C2|Bef], [C1|Aft], Rs) ->
    {{[C2,C1|Bef],Aft},[{put_chars, unicode,[C1,C2]},{move_rel,-1}|Rs]};
do_op(kill_word, Bef, Aft0, Rs) ->
    {Aft1,Kill0,N0} = over_non_word(Aft0, [], 0),
    {Aft,Kill,N} = over_word(Aft1, Kill0, N0),
    put(kill_buffer, reverse(Kill)),
    {{Bef,Aft},[{delete_chars,N}|Rs]};
do_op(backward_kill_word, Bef0, Aft, Rs) ->
    {Bef1,Kill0,N0} = over_non_word(Bef0, [], 0),
    {Bef,Kill,N} = over_word(Bef1, Kill0, N0),
    put(kill_buffer, Kill),
    {{Bef,Aft},[{delete_chars,-N}|Rs]};
do_op(kill_line, Bef, Aft, Rs) ->
    put(kill_buffer, Aft),
    {{Bef,[]},[{delete_chars,length(Aft)}|Rs]};
do_op(yank, Bef, [], Rs) ->
    Kill = get(kill_buffer),
    {{reverse(Kill, Bef),[]},[{put_chars, unicode,Kill}|Rs]};
do_op(yank, Bef, Aft, Rs) ->
    Kill = get(kill_buffer),
    {{reverse(Kill, Bef),Aft},[{insert_chars, unicode,Kill}|Rs]};
do_op(forward_char, Bef, [C|Aft], Rs) ->
    {{[C|Bef],Aft},[{move_rel,1}|Rs]};
do_op(backward_char, [C|Bef], Aft, Rs) ->
    {{Bef,[C|Aft]},[{move_rel,-1}|Rs]};
do_op(forward_word, Bef0, Aft0, Rs) ->
    {Aft1,Bef1,N0} = over_non_word(Aft0, Bef0, 0),
    {Aft,Bef,N} = over_word(Aft1, Bef1, N0),
    {{Bef,Aft},[{move_rel,N}|Rs]};
do_op(backward_word, Bef0, Aft0, Rs) ->
    {Bef1,Aft1,N0} = over_non_word(Bef0, Aft0, 0),
    {Bef,Aft,N} = over_word(Bef1, Aft1, N0),
    {{Bef,Aft},[{move_rel,-N}|Rs]};
do_op(beginning_of_line, [C|Bef], Aft, Rs) ->
    {{[],reverse(Bef, [C|Aft])},[{move_rel,-(length(Bef)+1)}|Rs]};
do_op(beginning_of_line, [], Aft, Rs) ->
    {{[],Aft},Rs};
do_op(end_of_line, Bef, [C|Aft], Rs) ->
    {{reverse(Aft, [C|Bef]),[]},[{move_rel,length(Aft)+1}|Rs]};
do_op(end_of_line, Bef, [], Rs) ->
    {{Bef,[]},Rs};
do_op(beep, Bef, Aft, Rs) ->
    {{Bef,Aft},[beep|Rs]};
do_op(_, Bef, Aft, Rs) ->
    {{Bef,Aft},[beep|Rs]}.

%% over_word(Chars, InitialStack, InitialCount) ->
%%	{RemainingChars,CharStack,Count}
%% over_non_word(Chars, InitialStack, InitialCount) ->
%%	{RemainingChars,CharStack,Count}
%%  Step over word/non-word characters pushing the stepped over ones on
%%  the stack.


over_word(Cs, Stack, N) ->
    L = length([1 || $\' <- Cs]),
    case L rem 2 of
	0 ->
	    over_word1(Cs, Stack, N);
	1 ->
	    until_quote(Cs, Stack, N)
    end.

until_quote([$\'|Cs], Stack, N) ->
    {Cs, [$\'|Stack], N+1};
until_quote([C|Cs], Stack, N) ->
    until_quote(Cs, [C|Stack], N+1).

over_word1([$\'=C|Cs], Stack, N) ->
    until_quote(Cs, [C|Stack], N+1);
over_word1(Cs, Stack, N) ->
    over_word2(Cs, Stack, N).

over_word2([C|Cs], Stack, N) ->
    case word_char(C) of
	true -> over_word2(Cs, [C|Stack], N+1);
	false -> {[C|Cs],Stack,N}
    end;
over_word2([], Stack, N) when is_integer(N) ->
    {[],Stack,N}.

over_non_word([C|Cs], Stack, N) ->
    case word_char(C) of
	true -> {[C|Cs],Stack,N};
	false -> over_non_word(Cs, [C|Stack], N+1)
    end;
over_non_word([], Stack, N) ->
    {[],Stack,N}.

word_char(C) when C >= $A, C =< $Z -> true;
word_char(C) when C >= $À, C =< $Þ, C =/= $× -> true;
word_char(C) when C >= $a, C =< $z -> true;
word_char(C) when C >= $ß, C =< $ÿ, C =/= $÷ -> true;
word_char(C) when C >= $0, C =< $9 -> true;
word_char(C) when C =:= $_ -> true;
word_char(C) when C =:= $. -> true;    % accept dot-separated names
word_char(_) -> false.

%% over_white(Chars, InitialStack, InitialCount) ->
%%	{RemainingChars,CharStack,Count}

%% over_white([$\s|Cs], Stack, N) ->
%%     over_white(Cs, [$\s|Stack], N+1);
%% over_white([$\t|Cs], Stack, N) ->
%%     over_white(Cs, [$\t|Stack], N+1);
%% over_white(Cs, Stack, N) ->
%%     {Cs,Stack,N}.

%% over_paren(Chars, Paren, Match)
%% over_paren(Chars, Paren, Match, Depth, N)
%%  Step over parentheses until matching Paren is found at depth 0. Don't
%%  do proper parentheses matching check. Paren has NOT been added.

over_paren(Chars, Paren, Match) ->
    over_paren(Chars, Paren, Match, 1, 1, []).


over_paren([C,$$,$$|Cs], Paren, Match, D, N, L)  ->
    over_paren([C|Cs], Paren, Match, D, N+2, L);
over_paren([_,$$|Cs], Paren, Match, D, N, L)  ->
    over_paren(Cs, Paren, Match, D, N+2, L);
over_paren([Match|_], _Paren, Match, 1, N, _) ->
    N;
over_paren([Match|Cs], Paren, Match, D, N, [Match|L]) ->
    over_paren(Cs, Paren, Match, D-1, N+1, L);
over_paren([Paren|Cs], Paren, Match, D, N, L) ->
    over_paren(Cs, Paren, Match, D+1, N+1, [Match|L]);

over_paren([$)|Cs], Paren, Match, D, N, L)  ->
    over_paren(Cs, Paren, Match, D, N+1, [$(|L]);
over_paren([$]|Cs], Paren, Match, D, N, L)  ->
    over_paren(Cs, Paren, Match, D, N+1, [$[|L]);
over_paren([$}|Cs], Paren, Match, D, N, L)  ->
    over_paren(Cs, Paren, Match, D, N+1, [${|L]);

over_paren([$(|Cs], Paren, Match, D, N, [$(|L])  ->
    over_paren(Cs, Paren, Match, D, N+1, L);
over_paren([$[|Cs], Paren, Match, D, N, [$[|L])  ->
    over_paren(Cs, Paren, Match, D, N+1, L);
over_paren([${|Cs], Paren, Match, D, N, [${|L])  ->
    over_paren(Cs, Paren, Match, D, N+1, L);

over_paren([$(|_], _, _, _, _, _)  ->
    beep;
over_paren([$[|_], _, _, _, _, _)  ->
    beep;
over_paren([${|_], _, _, _, _, _)  ->
    beep;

over_paren([_|Cs], Paren, Match, D, N, L)  ->
    over_paren(Cs, Paren, Match, D, N+1, L);
over_paren([], _, _, _, _, _) ->
    0.

over_paren_auto(Chars) ->
    over_paren_auto(Chars, 1, 1, []).


over_paren_auto([C,$$,$$|Cs], D, N, L)  ->
    over_paren_auto([C|Cs], D, N+2, L);
over_paren_auto([_,$$|Cs], D, N, L)  ->
    over_paren_auto(Cs, D, N+2, L);

over_paren_auto([$(|_], _, N, [])  ->
    {N, $)};
over_paren_auto([$[|_], _, N, [])  ->
    {N, $]};
over_paren_auto([${|_], _, N, [])  ->
    {N, $}};

over_paren_auto([$)|Cs], D, N, L)  ->
    over_paren_auto(Cs, D, N+1, [$(|L]);
over_paren_auto([$]|Cs], D, N, L)  ->
    over_paren_auto(Cs, D, N+1, [$[|L]);
over_paren_auto([$}|Cs], D, N, L)  ->
    over_paren_auto(Cs, D, N+1, [${|L]);

over_paren_auto([$(|Cs], D, N, [$(|L])  ->
    over_paren_auto(Cs, D, N+1, L);
over_paren_auto([$[|Cs], D, N, [$[|L])  ->
    over_paren_auto(Cs, D, N+1, L);
over_paren_auto([${|Cs], D, N, [${|L])  ->
    over_paren_auto(Cs, D, N+1, L);

over_paren_auto([_|Cs], D, N, L)  ->
    over_paren_auto(Cs, D, N+1, L);
over_paren_auto([], _, _, _) ->
    0.

%% erase_line(Line)
%% erase_inp(Line)
%% redraw_line(Line)
%% length_before(Line)
%% length_after(Line)
%% prompt(Line)
%%  Various functions for accessing bits of a line.

erase_line({line,Pbs,{Bef,Aft},_}) ->
    reverse(erase(Pbs, Bef, Aft, [])).

erase_inp({line,_,{Bef,Aft},_}) ->
    reverse(erase([], Bef, Aft, [])).

erase(Pbs, Bef, Aft, Rs) ->
    [{delete_chars,-length(Pbs)-length(Bef)},{delete_chars,length(Aft)}|Rs].

redraw_line({line,Pbs,{Bef,Aft},_}) ->
    reverse(redraw(Pbs, Bef, Aft, [])).

redraw(Pbs, Bef, Aft, Rs) ->
    [{move_rel,-length(Aft)},{put_chars, unicode,reverse(Bef, Aft)},{put_chars, unicode,Pbs}|Rs].

length_before({line,Pbs,{Bef,_Aft},_}) ->
    length(Pbs) + length(Bef).

length_after({line,_,{_Bef,Aft},_}) ->
    length(Aft).

prompt({line,Pbs,_,_}) ->
    Pbs.

%% %% expand(CurrentBefore) ->
%% %%	{yes,Expansion} | no
%% %%  Try to expand the word before as either a module name or a function
%% %%  name. We can handle white space around the seperating ':' but the
%% %%  function name must be on the same line. CurrentBefore is reversed
%% %%  and over_word/3 reverses the characters it finds. In certain cases
%% %%  possible expansions are printed.

%% expand(Bef0) ->
%%     {Bef1,Word,_} = over_word(Bef0, [], 0),
%%     case over_white(Bef1, [], 0) of
%% 	{[$:|Bef2],_White,_Nwh} ->
%% 	    {Bef3,_White1,_Nwh1} = over_white(Bef2, [], 0),
%% 	    {_,Mod,_Nm} = over_word(Bef3, [], 0),
%% 	    expand_function_name(Mod, Word);
%% 	{_,_,_} ->
%% 	    expand_module_name(Word)
%%     end.

%% expand_module_name(Prefix) ->
%%     match(Prefix, code:all_loaded(), ":").

%% expand_function_name(ModStr, FuncPrefix) ->
%%     Mod = list_to_atom(ModStr),
%%     case erlang:module_loaded(Mod) of
%% 	true ->
%% 	    L = apply(Mod, module_info, []),
%% 	    case lists:keyfind(exports, 1, L) of
%% 		{_, Exports} ->
%% 		    match(FuncPrefix, Exports, "(");
%% 		_ ->
%% 		    no
%% 	    end;
%% 	false ->
%% 	    no
%%     end.

%% match(Prefix, Alts, Extra) ->
%%     Matches = match1(Prefix, Alts),
%%     case longest_common_head([N || {N,_} <- Matches]) of
%% 	{partial, []} ->
%% 	    print_matches(Matches),
%% 	    no;
%% 	{partial, Str} ->
%% 	    case lists:nthtail(length(Prefix), Str) of
%% 		[] ->
%% 		    print_matches(Matches),
%% 		    {yes, []};
%% 		Remain ->
%% 		    {yes, Remain}
%% 	    end;
%% 	{complete, Str} ->
%% 	    {yes, lists:nthtail(length(Prefix), Str) ++ Extra};
%% 	no ->
%% 	    no
%%     end.

%% %% Print the list of names L in multiple columns.
%% print_matches(L) ->
%%     io:nl(),
%%     col_print(lists:sort(L)),
%%     ok.

%% col_print([]) -> ok;
%% col_print(L)  -> col_print(L, field_width(L), 0).

%% col_print(X, Width, Len) when Width + Len > 79 ->
%%     io:nl(),
%%     col_print(X, Width, 0);
%% col_print([{H0,A}|T], Width, Len) ->
%%     H = if
%% 	    %% If the second element is an integer, we assume it's an
%% 	    %% arity, and meant to be printed.
%% 	    integer(A) ->
%% 		H0 ++ "/" ++ integer_to_list(A);
%% 	    true ->
%% 		H0
%% 	end,
%%     io:format("~-*s",[Width,H]),
%%     col_print(T, Width, Len+Width);
%% col_print([], _, _) ->
%%     io:nl().

%% field_width([{H,_}|T]) -> field_width(T, length(H)).

%% field_width([{H,_}|T], W) ->
%%     case length(H) of
%% 	L when L > W -> field_width(T, L);
%% 	_ -> field_width(T, W)
%%     end;
%% field_width([], W) when W < 40 ->
%%     W + 4;
%% field_width([], _) ->
%%     40.

%% match1(Prefix, Alts) ->
%%     match1(Prefix, Alts, []).

%% match1(Prefix, [{H,A}|T], L) ->
%%     case prefix(Prefix, Str = atom_to_list(H)) of
%% 	true ->
%% 	    match1(Prefix, T, [{Str,A}|L]);
%% 	false ->
%% 	    match1(Prefix, T, L)
%%     end;
%% match1(_, [], L) ->
%%     L.

%% longest_common_head([]) ->
%%     no;
%% longest_common_head(LL) ->
%%     longest_common_head(LL, []).

%% longest_common_head([[]|_], L) ->
%%     {partial, reverse(L)};
%% longest_common_head(LL, L) ->
%%     case same_head(LL) of
%% 	true ->
%% 	    [[H|_]|_] = LL,
%% 	    LL1 = all_tails(LL),
%% 	    case all_nil(LL1) of
%% 		false ->
%% 		    longest_common_head(LL1, [H|L]);
%% 		true ->
%% 		    {complete, reverse([H|L])}
%% 	    end;
%% 	false ->
%% 	    {partial, reverse(L)}
%%     end.

%% same_head([[H|_]|T1]) -> same_head(H, T1).

%% same_head(H, [[H|_]|T]) -> same_head(H, T);
%% same_head(_, [])        -> true;
%% same_head(_, _)         -> false.

%% all_tails(LL) -> all_tails(LL, []).

%% all_tails([[_|T]|T1], L) -> all_tails(T1, [T|L]);
%% all_tails([], L)         -> L.

%% all_nil([]) -> true;
%% all_nil([[] | Rest]) -> all_nil(Rest);
%% all_nil(_) -> false.
