When experimenting in the Erlang shell I have often felt the need to
grab history entries and rewrite them. Unfortunately, the Erlang history
command h() only gives you a printout of the history.

So yesterday I wrote this function:

hist() ->
  {links, [Shell|_]} = hd(process_info(self(), [links])),
  Shell ! {shell_req, self(), get_cmd},
  receive 
   {shell_rep, Shell, R} -> R 
  end.

Which (from the shell) returns the shell history as an Erlang term.

I also wrote a function to just get the commands:

get_command_hist() ->
  H = hist(),
  lists:sort([{N,Cmd} || {{command, N}, Cmd} <- H]).

And a function to format them “nicely”:

%% @doc Pretty prints an enumerated list
%%      of commands from the history,
list() ->
  CommandHist = get_command_hist(),
  [case Trees of 
    [] -> ok;
    [T] -> 
      io:format("~w: ~s.~n",
                [N, erl_prettypr:format(T)]);
    [T|Ts] ->
      io:format("~w: ~s~s.~n",
                [N, erl_prettypr:format(T), 
                [", "++erl_prettypr:format(Tree)
                 || Tree <- Ts]])
   end || {N, Trees} <- CommandHist],
  ok.

Well, ok now I am back where I started with only a printout…
but by using hist instead of list I can do interesting things, like
grabbing a pice of history and turn it into a function:

-spec grab(Start::integer(), Stop::integer(),
           Exclude::[integer()], Name::atom())
          -> syntax_tools:syntax_tree().
%% @doc Creates a syntax tree for a function called Name from
%%      the commands in the history between Start and Stop,
%%      excluding the history lines enumerated in Exclude.
grab(Start, Stop, Exclude, Name) ->
    CommandHist = get_command_hist(),
    ListOfTrees = filter_range(CommandHist, Start,
                               Stop, Exclude),
    Tree = lists:append(ListOfTrees),
    Args = get_free_variables(Tree),
    Clause = [erl_syntax:clause(Args,[],Tree)],
    erl_syntax:function(erl_syntax:atom(Name), Clause).

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