Introduce the ?TYPE macro

It allows explicitly using PropEr's "native types" feature.

This is more powerful than the current automatic parse transform-based inference:
* it can be used outside of `?FORALL` to produce PropEr types & combine
  them with other PropEr or native types.
* it allows using the "native types" feature with the proper parse transform disabled
* it allows expressing more types directly, without creating additional type aliases,
  for example: `?TYPE(atom() | float())`.

The semantics are identical to automatic inference, if the expression was wrapped
in a simple `id` type (when the syntax allows expressing such a type). For example:

```erlang
-record(foo, {}).
-type id(X) :: X.

% semantically equivalent definitions:
?FORALL(X, id(#foo{}), Prop).
?FORALL(X, ?TYPE(#foo{}), Prop).
```

include/proper_common.hrl

@@ -61,6 +61,7 @@
         proper_types:add_constraint(RawType,fun(X) -> Condition end,true)).
 -define(SUCHTHATMAYBE(X,RawType,Condition),
         proper_types:add_constraint(RawType,fun(X) -> Condition end,false)).
+-define(TYPE(X), proper_types:native_type(?MODULE, ??X)).
 
 %%------------------------------------------------------------------------------
 %% Targeted macros

src/proper_typeserver.erl

@@ -27,16 +27,23 @@
 %%%
 %%% PropEr can parse types expressed in Erlang's type language and convert them
 %%% to its own type format. Such expressions can be used instead of regular type
-%%% constructors in the second argument of `?FORALL's. No extra notation is
-%%% required; PropEr will detect which calls correspond to native types by
-%%% applying a parse transform during compilation. This parse transform is
-%%% automatically applied to any module that includes the `proper.hrl' header
-%%% file. You can disable this feature by compiling your modules with
-%%% `-DPROPER_NO_TRANS'. Note that this will currently also disable the
-%%% automatic exporting of properties.
+%%% constructors in the second argument of `?FORALL's. Such types can be expressed
+%%% in two ways:
+%%% <ul>
+%%% <li> directly, with no extra notation required; PropEr will detect which calls
+%%% correspond to native types by applying a parse transform during compilation.
+%%% This parse transform is automatically applied to any module that includes
+%%% the `proper.hrl' header file.</li>
+%%% <li> by leveraging the `?TYPE` macro; This allows urestricted use of Erlang's
+%%% type language and does not require applying the parse transform.</li>
+%%% </ul>
+%%%
+%%% You can disable the parse transform (and automatic detection of native types)
+%%% by compiling your modules with `-DPROPER_NO_TRANS' flag. Note that this will
+%%% currently also disable the automatic exporting of properties.
 %%%
-%%% The use of native types in properties is subject to the following usage
-%%% rules:
+%%% The use of automatically-detected native types in properties is subject
+%%% to the following usage rules:
 %%% <ul>
 %%% <li>Native types cannot be used outside of `?FORALL's.</li>
 %%% <li>Inside `?FORALL's, native types can be combined with other native
@@ -154,6 +161,19 @@
 %%% </li>
 %%% </ul>
 %%%
+%%% The `?TYPE` macro for explicitly taking advantage of PropEr's native type
+%%% support is subject to the following usage rules:
+%%% <ul>
+%%% <li>It is allowed in any position to produce a PropEr type, including
+%%%   outside of `?FORALL`.</li>
+%%% <li>The same restriction on allowed recursive native types as in `?FORALL` apply.</li>
+%%% <li>There's no risk of confusion between expressions and native types,
+%%%   inside `?TYPE` everything is interpreted as a native type, and as such
+%%%   `?TYPE([integer()])` will produce an arbitrary integer list.</li>
+%%% <li>It is not checked for correct syntax - using invalid syntax can produce
+%%%   errors when the property is evaluated, which are hard to understand.</li>
+%%% </ul>
+%%%
 %%% You can use <a href="#index">these</a> functions to try out the type
 %%% translation subsystem.
 %%%

test/no_transforms.erl

@@ -0,0 +1,42 @@
+%%% -*- coding: utf-8 -*-
+%%% -*- erlang-indent-level: 2 -*-
+%%% -------------------------------------------------------------------
+%%% Copyright 2010-2011 Manolis Papadakis <[email protected]>,
+%%%                     Eirini Arvaniti <[email protected]>
+%%%                 and Kostis Sagonas <[email protected]>
+%%%
+%%% This file is part of PropEr.
+%%%
+%%% PropEr is free software: you can redistribute it and/or modify
+%%% it under the terms of the GNU General Public License as published by
+%%% the Free Software Foundation, either version 3 of the License, or
+%%% (at your option) any later version.
+%%%
+%%% PropEr is distributed in the hope that it will be useful,
+%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%%% GNU General Public License for more details.
+%%%
+%%% You should have received a copy of the GNU General Public License
+%%% along with PropEr.  If not, see <http://www.gnu.org/licenses/>.
+
+%%% @copyright 2010-2011 Manolis Papadakis, Eirini Arvaniti and Kostis Sagonas
+%%% @version {@version}
+%%% @doc This module tests whether proper works with parse transforms disabled.
+
+-module(no_transforms).
+-export([prop_1/0, prop_2/0]).
+
+-define(PROPER_NO_TRANS, true).
+
+-include_lib("proper/include/proper.hrl").
+
+-type local_integer() :: integer().
+-type local_float() :: float().
+
+prop_1() -> ?FORALL(X, ?TYPE(local_integer() | local_float()), is_number(X)).
+
+prop_2() -> ?FORALL(X, native_type(), is_integer(X) orelse is_atom(X)).
+
+native_type() ->
+    ?TYPE(local_integer() | atom()).

test/proper_tests.erl

@@ -837,7 +837,9 @@ parse_transform_test_() ->
      ?_assertError(undef, auto_export_test2:prop_1()),
      ?_assertError(undef, no_native_parse_test:prop_1()),
      ?_passes(let_tests:prop_1()),
-     ?_failsWith([3*42], let_tests:prop_2())].
+     ?_failsWith([3*42], let_tests:prop_2()),
+     ?_passes(no_transforms:prop_1()),
+     ?_passes(no_transforms:prop_2())].
 
 native_type_props_test_() ->
     [?_passes(?FORALL({X,Y}, {my_native_type(),my_proper_type()},