[Distel-hackers] First "refactoring" command

[Luke G. <lu...@bl...>]

Hello everyone, welcome to the year 2003 :-)

I just checked in a refactoring command in CVS, called
erl-refactor-subfunction, and bound to "C-c C-d f".

Suppose we have a function like this:

  eval_expression(S) ->
      case parse_expr(S) of
          {ok, Parse} ->
              case catch erl_eval:exprs(Parse, []) of
                  {value, V, _} ->
                      {ok, flatten(io_lib:format("~p", [V]))};
                  {'EXIT', Reason} ->
                      {error, Reason}
              end;
          {error, {_, erl_parse, Err}} ->
              {error, Err}
      end.

Futher suppose that we want to tidy up by making the 'case' expression
into a separate function. We can do this automatically, by first
selecting the region from 'case' to 'end', and then running
erl-refactor-subfunction. It will prompt us for for the name of our
new function, and we can enter "try_evaluation". It then replaces the
'case' expression with a call to our new function, passing in any
variable(s) it needs, so we end up with:

  eval_expression(S) ->
      case parse_expr(S) of
	  {ok, Parse} ->
	      try_evaluation(Parse);
	  {error, {_, erl_parse, Err}} ->
	      {error, Err}
      end.

Which is all good and well, but we still need the actual function
definition. That gets put on the kill ring, so that we can put it
where we want manually. So, the next time we "yank" with C-y, we will
get:

  try_evaluation(Parse) ->
      case catch erl_eval:exprs(Parse, []) of
	  {value, V, _} ->
	      {ok, flatten(io_lib:format("~p", [V]))};
	  {'EXIT', Reason} ->
	      {error, Reason}
      end.

And then our program works again!

One caveat: any variable bindings created in the new function will
not get exported back out, so it's possibly to break a program with
this command if you use it recklessly :-)

Thanks to Richard Carlsson for doing all the work! And for
demonstrating how bloody easy it is to use his syntax_tools package
:-)

P.S.: You have to download syntax_tools 1.2 and stick it in your load
path (e.g. using the ~/.erlang file) for this to work. You can
download it from erlang.org's contributions page.

(Sorry about the delay in implementing this, Richard. I needed a
while to write enough sufficiently ugly code to motivate it :-))

Cheers,
Luke