readtags: S expression based filter engine like wireshark's display filter

[masatake]

(Request for reviewer: I wonder which is better "filter" or "qualifier" for this feature. filter looks better but it misleads "pipe and filter" of command line interface. Give me advise if you like this feature.)

Examples of input

Make tags(*foo.tags*) with following command line

.. code-block:: console

    $ ./ctags --fields='*' --extra='*' -o foo.tags foo.py

for following input (*foo.py*)

.. code-block:: Python

    class Foo:
    def aq ():
        pass
    def aw ():
        pass
    def ae ():
        pass
    class A:
        pass
    class Bar (Foo):
    def bq ():
        pass
    def bw ():
        pass
    class B:
        pass

    class Baz (Foo):
    def bq ():
        pass
    def bw ():
        pass
    class C:
        pass

Examples of filter expressions

• Print entries ended with "q"

  .. code-block:: console

  $ ./readtags -e -t foo.tags -Q '(suffix? $name "q")' -l
  Bar.bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Bar access:public signature:()
  Baz.bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  Foo.aq foo.py /^ def aq ():$/;" kind:member language:Python scope:class:Foo access:public signature:()
  aq foo.py /^ def aq ():$/;" kind:member language:Python scope:class:Foo access:public signature:()
  bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Bar access:public signature:()
  bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Baz access:public signature:()

• Print members of Baz

  .. code-block:: console

  $ ./readtags -e -t foo.tags -Q '(and (eq? $kind "member") (eq? "Baz" $scope-name))' -l
  Baz.bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  Baz.bw foo.py /^ def bw ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  bw foo.py /^ def bw ():$/;" kind:member language:Python scope:class:Baz access:public signature:()

• Print only full qualified entries (assuming "." is used as the separator)

  .. code-block:: console

  $ ./readtags -e -t foo.tags -Q '(and (eq? $kind "member") (substr? $name "."))' -l
  Bar.bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Bar access:public signature:()
  Bar.bw foo.py /^ def bw ():$/;" kind:member language:Python scope:class:Bar access:public signature:()
  Baz.bq foo.py /^ def bq ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  Baz.bw foo.py /^ def bw ():$/;" kind:member language:Python scope:class:Baz access:public signature:()
  Foo.ae foo.py /^ def ae ():$/;" kind:member language:Python scope:class:Foo access:public signature:()
  Foo.aq foo.py /^ def aq ():$/;" kind:member language:Python scope:class:Foo access:public signature:()
  Foo.aw foo.py /^ def aw ():$/;" kind:member language:Python scope:class:Foo access:public signature:()

• Print only inheriting specified classes

  .. code-block:: console

  $ ./readtags -e -t foo.tags -Q '(and (member "Foo" $inherits) (eq? $kind "class"))' -l
  Bar foo.py /^class Bar (Foo):$/;" kind:class language:Python inherits:Foo access:public
  Baz foo.py /^class Baz (Foo): $/;" kind:class language:Python inherits:Foo access:public

[masatake]

TODO: lambda and map are not there.

Eventually a real interpreter like lua or siod will be needed. I don't know lua so siod is better for me.
We can keep the current syntax proposed in this PR even if we introduce siod(scheme in one defun).

Some work about build script will be needed to introduce siod.
With build-in script language you can write parser, formatter, sorting and filtering rule.