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version 2230, Sun Sep 3 15:57:44 2006 UTC version 2234, Sun Sep 3 19:31:05 2006 UTC
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 the work needed to transform tree-like structures into linear bytecode  the work needed to transform tree-like structures into linear bytecode
 instructions, and includes the ability to do compile-time constant folding.  instructions, and includes the ability to do compile-time constant folding.
   
   Changes since version 0.2:
   
   * The ``repr()`` of AST nodes doesn't include a trailing comma for 1-argument
     node types any more.
   
   * Added a ``Pass`` symbol that generates no code, a ``Compare()`` node type
     that does n-way comparisons, and ``And()`` and ``Or()`` node types for doing
     logical operations.
   
   * The ``COMPARE_OP()`` method now accepts operator strings like ``"<="``,
     ``"not in"``, ``"exception match"``, and so on, as well as numeric opcodes.
     See the standard library's ``opcode`` module for a complete list of the
     strings accepted (in the ``cmp_op`` tuple).  ``"<>"`` is also accepted as an
     alias for ``"!="``.
   
 Changes since version 0.1:  Changes since version 0.1:
   
 * Constant handling has been fixed so that it doesn't confuse equal values of  * Constant handling has been fixed so that it doesn't confuse equal values of
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     >>> c.LOAD_CONST(None)  # in real code, this'd be a Python code constant      >>> c.LOAD_CONST(None)  # in real code, this'd be a Python code constant
     >>> c.MAKE_CLOSURE(0,2) # no defaults, 2 free vars in the new function      >>> c.MAKE_CLOSURE(0,2) # no defaults, 2 free vars in the new function
   
   The ``COMPARE_OP`` method takes an argument which can be a valid comparison
   integer constant, or a string containing a Python operator, e.g.::
   
       >>> c = Code()
       >>> c.LOAD_CONST(1)
       >>> c.LOAD_CONST(2)
       >>> c.COMPARE_OP('not in')
       >>> dis(c.code())
         0           0 LOAD_CONST               1 (1)
                     3 LOAD_CONST               2 (2)
                     6 COMPARE_OP               7 (not in)
   
   The full list of valid operator strings can be found in the standard library's
   ``opcode`` module.  ``"<>"`` is also accepted as an alias for ``"!="``::
   
       >>> c.LOAD_CONST(3)
       >>> c.COMPARE_OP('<>')
       >>> dis(c.code())
         0           0 LOAD_CONST               1 (1)
                     3 LOAD_CONST               2 (2)
                     6 COMPARE_OP               7 (not in)
                     9 LOAD_CONST               3 (3)
                    12 COMPARE_OP               3 (!=)
   
   
 High-Level Code Generation  High-Level Code Generation
 ==========================  ==========================
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     AssertionError: Label previously defined      AssertionError: Label previously defined
   
   
   N-Way Comparisons
   -----------------
   
   You can generate N-way comparisons using the ``Compare()`` node type::
   
       >>> from peak.util.assembler import Compare
   
       >>> c = Code()
       >>> c(Compare(Local('a'), [('<', Local('b'))]))
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (a)
                     3 LOAD_FAST                1 (b)
                     6 COMPARE_OP               0 (<)
   
   3-way comparisons generate code that's a bit more complex.  Here's a three-way
   comparison (``a<b<c``)::
   
       >>> c = Code()
       >>> c.return_(Compare(Local('a'), [('<', Local('b')), ('<', Local('c'))]))
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (a)
                     3 LOAD_FAST                1 (b)
                     6 DUP_TOP
                     7 ROT_THREE
                     8 COMPARE_OP               0 (<)
                    11 JUMP_IF_FALSE           10 (to 24)
                    14 POP_TOP
                    15 LOAD_FAST                2 (c)
                    18 COMPARE_OP               0 (<)
                    21 JUMP_FORWARD             2 (to 26)
               >>   24 ROT_TWO
                    25 POP_TOP
               >>   26 RETURN_VALUE
   
   And a four-way (``a<b>c!=d``)::
   
       >>> c = Code()
       >>> c.return_(
       ...     Compare( Local('a'), [
       ...         ('<', Local('b')), ('>', Local('c')), ('!=', Local('d'))
       ...     ])
       ... )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (a)
                     3 LOAD_FAST                1 (b)
                     6 DUP_TOP
                     7 ROT_THREE
                     8 COMPARE_OP               0 (<)
                    11 JUMP_IF_FALSE           22 (to 36)
                    14 POP_TOP
                    15 LOAD_FAST                2 (c)
                    18 DUP_TOP
                    19 ROT_THREE
                    20 COMPARE_OP               4 (>)
                    23 JUMP_IF_FALSE           10 (to 36)
                    26 POP_TOP
                    27 LOAD_FAST                3 (d)
                    30 COMPARE_OP               3 (!=)
                    33 JUMP_FORWARD             2 (to 38)
               >>   36 ROT_TWO
                    37 POP_TOP
               >>   38 RETURN_VALUE
   
   
 Constant Detection and Folding  Constant Detection and Folding
 ==============================  ==============================
   
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 ``globals()``, in other words.  ``globals()``, in other words.
   
   
   Logical And/Or
   --------------
   
   You can evaluate logical and/or expressions using the ``And`` and ``Or`` node
   types::
   
       >>> from peak.util.assembler import And, Or
   
       >>> c = Code()
       >>> c.return_( And([Local('x'), Local('y')]) )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (x)
                     3 JUMP_IF_FALSE            4 (to 10)
                     6 POP_TOP
                     7 LOAD_FAST                1 (y)
               >>   10 RETURN_VALUE
   
       >>> c = Code()
       >>> c.return_( Or([Local('x'), Local('y')]) )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (x)
                     3 JUMP_IF_TRUE             4 (to 10)
                     6 POP_TOP
                     7 LOAD_FAST                1 (y)
               >>   10 RETURN_VALUE
   
   
   True or false constants are folded automatically, avoiding code generation
   for intermediate values that will never be used in the result::
   
       >>> c = Code()
       >>> c.return_( And([1, 2, Local('y')]) )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (y)
                     3 RETURN_VALUE
   
       >>> c = Code()
       >>> c.return_( And([1, 2, Local('y'), 0]) )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (y)
                     3 JUMP_IF_FALSE            4 (to 10)
                     6 POP_TOP
                     7 LOAD_CONST               1 (0)
               >>   10 RETURN_VALUE
   
       >>> c = Code()
       >>> c.return_( Or([1, 2, Local('y')]) )
       >>> dis(c.code())
         0           0 LOAD_CONST               1 (1)
                     3 RETURN_VALUE
   
       >>> c = Code()
       >>> c.return_( Or([False, Local('y'), 3]) )
       >>> dis(c.code())
         0           0 LOAD_FAST                0 (y)
                     3 JUMP_IF_TRUE             4 (to 10)
                     6 POP_TOP
                     7 LOAD_CONST               1 (3)
               >>   10 RETURN_VALUE
   
   
 Custom Code Generation  Custom Code Generation
 ======================  ======================
   
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 If you want to incorporate constant-folding into your AST nodes, you can do  If you want to incorporate constant-folding into your AST nodes, you can do
 so by checking for constant values and folding them at either construction  so by checking for constant values and folding them at either construction
 or code generation time.  For example, this ``And`` node type folds constants  or code generation time.  For example, this ``And`` node type (a simpler
 during code generation, by not generating unnecessary branches when it can  version of the one included in ``peak.util.assembler``) folds constants during
   code generation, by not generating unnecessary branches when it can
 prove which way a branch will go::  prove which way a branch will go::
   
     >>> from peak.util.assembler import NotAConstant      >>> from peak.util.assembler import NotAConstant
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 code that might be unreachable.  For example, consider this ``If``  code that might be unreachable.  For example, consider this ``If``
 implementation::  implementation::
   
     >>> def Pass(code=None):      >>> from peak.util.assembler import Pass
     ...     if code is None:  
     ...         return Pass  
   
     >>> def If(cond, then, else_=Pass, code=None):      >>> def If(cond, then, else_=Pass, code=None):
     ...     if code is None:      ...     if code is None:
     ...         return cond, then, else_      ...         return cond, then, else_

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