PyPy, like any large project, has developed a jargon of its own.  This
document gives brief definition of some of these terms and provides
links to more information.

**abstract interpretation**
    The technique of interpreting the bytecode of a user program with
    an interpreter that handles abstract objects instead of concrete ones.
    It can be used to check the bytecode or see what it does, without
    actually executing it with concrete values.  See Theory_.

.. _annotator:

**annotator**
    The component of the translator_\ 's toolchain_ that performs a form
    of `type inference`_ on the flow graph. See the `annotator pass`_
    in the documentation.

.. _`application level`:

**application level**
    applevel_ code is normal Python code running on top of the PyPy or
    CPython_ interpreter (see `interpreter level`_)

.. _backend:

**backend**
    Code generator that converts an `RPython
    <coding-guide.html#restricted-python>`__ program to a `target
    language`_ using the PyPy toolchain_. A backend uses either the
    lltypesystem_ or the ootypesystem_.

.. _`compile-time`:

**compile-time**
    In the context of the JIT_, compile time is when the JIT is
    generating machine code "just in time".

.. _CPython:

**CPython**
    The "default" implementation of Python, written in C and
    distributed by the PSF_ on http://www.python.org.

.. _`external function`:

**external function**
    Functions that we don't want to implement in Python for various
    reasons (e.g. they need to make calls into the OS) and whose
    implementation will be provided by the backend.

.. _`garbage collection framework`:

**garbage collection framework**
    Code that makes it possible to write `PyPy's garbage collectors`_
    in Python itself.

.. _`interpreter level`:

**interpreter level**
    Code running at this level is part of the implementation of the
    PyPy interpreter and cannot interact normally with `application
    level`_ code; it typically provides implementation for an object
    space and its builtins.

.. _`jit`:

**jit**
  `just in time compiler`_.

.. _llinterpreter:

**llinterpreter**
   Piece of code that is able to interpret flow graphs.  This is very
   useful for testing purposes, especially if you work on the RPython_
   Typer.

.. _lltypesystem:

**lltypesystem**
   A `C-like type model <rtyper.html#low-level-types>`__ that contains
   structs and pointers.  A backend_ that uses this type system is also
   called a low-level backend.  The C backend uses this
   typesystem.

.. _`low-level helper`:

**low-level helper**
    A function that the RTyper_ can use a call to as part of implementing
    some operation in terms of the target `type system`_.

.. _`mixed module`:

**mixed module**
  a module that accesses PyPy's `interpreter level`_.  The name comes
  from the fact that the module's implementation can be a mixture of
  `application level`_ and `interpreter level`_ code.

.. _`object space`:

**multimethod**
   A callable object that invokes a different Python function based
   on the type of all its arguments (instead of just the class of the
   first argument, as with normal methods).  See Theory_.

**object space**
   The `object space <objspace.html>`__ (often abbreviated to
   "objspace") creates all objects and knows how to perform operations
   on the objects. You may think of an object space as being a library
   offering a fixed API, a set of operations, with implementations
   that a) correspond to the known semantics of Python objects, b)
   extend or twist these semantics, or c) serve whole-program analysis
   purposes.

.. _ootypesystem:

**ootypesystem**
   An `object oriented type model <rtyper.html#object-oriented-types>`__
   containing classes and instances.  A backend_ that uses this type system
   is also called a high-level backend.  The JVM and CLI backends 
   all use this typesystem.

.. _`prebuilt constant`:

**prebuilt constant**
   In RPython_ module globals are considered constants.  Moreover,
   global (i.e. prebuilt) lists and dictionaries are supposed to be
   immutable ("prebuilt constant" is sometimes abbreviated to "pbc").

.. _`rpython`:

.. _`promotion`:

**promotion**
   JIT_ terminology.  *promotion* is a way of "using" a `run-time`_
   value at `compile-time`_, essentially by deferring compilation
   until the run-time value is known. See if `the jit docs`_ help.

**rpython**
   `Restricted Python`_, a limited subset of the Python_ language.
   The limitations make `type inference`_ possible.
   It is also the language that the PyPy interpreter itself is written
   in.

.. _`rtyper`:

**rtyper**
   Based on the type annotations, the `RPython Typer`_ turns the flow
   graph into one that fits the model of the target platform/backend_
   using either the lltypesystem_ or the ootypesystem_.

.. _`run-time`:

**run-time**
   In the context of the JIT_, run time is when the code the JIT has
   generated is executing.

.. _`specialization`:

**specialization**
   A way of controlling how a specific function is handled by the
   annotator_.  One specialization is to treat calls to a function
   with different argument types as if they were calls to different
   functions with identical source.

.. _`stackless`:

**stackless**
    Technology that enables various forms of non conventional control
    flow, such as coroutines, greenlets and tasklets.  Inspired by
    Christian Tismer's `Stackless Python <http://www.stackless.com>`__.

.. _`standard interpreter`:

**standard interpreter**
   It is the `subsystem implementing the Python language`_, composed
   of the bytecode interpreter and of the standard objectspace.

.. _toolchain:

**timeshifting**
   JIT_ terminology.  *timeshifting* is to do with moving from the
   world where there are only `run-time`_ operations to a world where
   there are both `run-time`_ and `compile-time`_ operations.

**toolchain**
   The `annotator pass`_, `The RPython Typer`_, and various
   `backends`_.

.. _`transformation`:

**transformation**
   Code that modifies flowgraphs to weave in `translation-aspects`_

.. _`translation-time`:

**translation-time**
   In the context of the JIT_, translation time is when the PyPy
   source is being analysed and the JIT itself is being created.

.. _`translator`:

**translator**
  Tool_ based on the PyPy interpreter which can translate
  sufficiently static Python programs into low-level code.

.. _`type system`:

**type system**
    The RTyper can target either the lltypesystem_ or the ootypesystem_.

.. _`type inference`:

**type inference**
   Deduces either partially or fully the type of expressions as
   described in this `type inference article on Wikipedia`_.
   PyPy's tool-chain own flavour of type inference is described
   in the `annotator pass`_ section.

.. _applevel: coding-guide.html#application-level
.. _`target language`: getting-started-dev.html#trying-out-the-translator
.. _`just in time compiler`: jit/index.html
.. _`the jit docs`: jit/index.html
.. _`type inference article on Wikipedia`: http://en.wikipedia.org/wiki/Type_inference
.. _`annotator pass`: translation.html#the-annotation-pass
.. _`The RPython Typer`: translation.html#the-rpython-typer
.. _`backends`: getting-started-dev.html#trying-out-the-translator
.. _Tool: getting-started-dev.html#trying-out-the-translator
.. _`translation-aspects`: translation-aspects.html
.. _`PyPy's garbage collectors`: garbage_collection.html
.. _`Restricted Python`: coding-guide.html#restricted-python
.. _PSF: http://www.python.org/psf/
.. _Python: http://www.python.org
.. _`RPython Typer`: rtyper.html
.. _`subsystem implementing the Python language`: architecture.html#standard-interpreter
.. _Theory: theory.html

.. include:: _ref.txt