detab

#!/usr/bin/env escript

%% settabs -- set initial tab stops
%%
%% We can't generate a list/array because we don't have a MAXLINE.
%% settabs returns the TabSpace value instead.
settabs() ->
    TabSpace = 4,
    TabSpace.

%% tabpos -- return true if col is a tab stop
%%
%% Doesn't make sense in using MAXLINE since Erlang handle
%% the EOF and buffer size for us, unless we're using
%% io:get_chars/2 because the second parameter of the said
%% function is exactly a limiter.
tabpos(Col) ->
    TabSpace = settabs(),
    TabSpace - Col rem TabSpace.

%% detab - convert tabs to blanks
%%
%% It doesn't work exactely as the Pascal version.
%% See settabs/0 and tappos/1 for details.
%%
%% BUGS
%% Special characters other than 9, 10, 32 might transform
%% the return string in numbers and screw everything.
detab() ->
    Input = ststd:getf(),
    detab(Input, 0, []).

detab([], _, Acc) ->
    ststd:putf("~p~n", [Acc]);
detab([9|T], Col, Acc) ->
    Feed = tabpos(Col),
    Blanks = lists:map(fun(_) -> 32 end, lists:seq(1, Feed)),
    detab(T, Col+Feed, lists:concat([Acc, Blanks]));
detab([H|T], Col, Acc) ->
    detab(T, Col+1, lists:concat([Acc, [H]])).


main([]) ->
    detab();
main(Arg) ->
    {ok, Bin} = file:read_file(Arg),
    File = erlang:binary_to_list(Bin),
    detab(File, 0, []).