list match (last N character match) - erlang

Question

I am writing hg(mercurial)'s client now. For tags commands, the reponse is as follows:
<<"adding a\na\ncommitted changeset
0:44108598f0ec643e7d90e9f18a2b6740401a510a\ntip
1:ce4daf41b6ae\nmy tags
0:44108598f0ec\ntest tag 0:44108598f0ec
local\n">>.
The python's related code is as follows:
t = []
for line in out.splitlines():
taglocal = line.endswith(' local')
if taglocal:
line = line[:-6]
name, rev = line.rsplit(' ', 1)
rev, node = rev.split(':')
t.append((name.rstrip(), int(rev), node, taglocal))
return t
I have to check everyline for "local" postfix, but the compiler give syntax error. How to write correctly and elegant.
error message:
src/emercurial_client.erl:763: illegal pattern
Code
process_tags(List)->
process_tags(List,[]).
process_tags([],Result)->
lists:reverse(Result);
process_tags([Line|Rest],Result) ->
B = binary_to_list(Line),
A = process_tags_line(B),
process_tags(Rest,[A|Result]).
process_tags_line(New_list ++"local")-> %%<-----error here
process_tags_line(New_list);
process_tags_line(New_list)->
%% case List of
%% Data ++ " local" -> %%<-----also match error
%% New_list = Data;
%% _ ->
%% New_list = List
%% end,
[Name,Part2] = string:tokens(Data," "),
[Rev,Node] = string:tokens(Part2,":"),
{trim(Name),love_misc:to_integer(Rev),
node,New_list}.
After modification, it is follows:
process_tags(List)->
List_b = binary:split(List,<<$\n>>,[global]),
Result = process_tags(List_b,[]),
%% error_logger:info_report([client_process_tags,Result]),
Result.
process_tags([],Result)->
lists:reverse(Result);
process_tags([<<>>],Result)->
lists:reverse(Result);
process_tags([Line|Rest],Result) ->
B = binary_to_list(Line),
A = process_tags_line(B),
process_tags(Rest,[A|Result]).
process_tags_line(List) ->
%% error_logger:info_report([client_tags_line_1,List]),
case lists:suffix(" local",List) of
true ->
New_list = lists:sublist(List,1,length(List)-7);
_ ->
New_list = List
end,
{Name,Part2} = rsplit(New_list,$\s),
{Rev,Node} =
rsplit(Part2,$:),
Rev_a = string:substr(Rev,1,length(Rev)-1),
{love_misc:trim(Name),love_misc:to_integer(Rev_a),Node,New_list}.
rsplit(A,Char)->
Index = string:rchr(A,Char),
lists:split(Index,A).

Answer 1

As pointed in documentation, you can match only prefixes in similar way (which in fact just a syntactic sugar).
I'd suggest you to use function lists:suffix
So, you can rewrite your code in such way:
New_list =
case lists:suffix(" local", List) of
true ->
Data;
false ->
List
end
Note, that case expressions returns values, so you can bind variable New_List only once - with result of case expression, instead of binding in each branch of case expression

Answer 2

I think you cannot use this pattern matching because of the underlying structure of a list ([A|[B|[....|[]...]]).
The reverse works so you can do something like
process_tags_line(List) ->
process_tags_line_1(lists:reverse(List)).
process_tags_line1(" lacol"++L) -> process_tags_line1(L);
process_tags_line1(L) ->
New_list = lists:reverse(L),
[Name,Part2] = string:tokens(Data," "),
[Rev,Node] = string:tokens(Part2,":"),
{trim(Name),love_misc:to_integer(Rev),node,New_list}.
But the simplest thing may be to use lists:suffix(L1,L2)...