[Cython] Lisp inspired transforms

[Martin C. Martin]

Hi all,

I've been doing some thinking and prototyping of a transform system 
inspired by Common Lisp macros.  You can see the results as the newest CEP:

http://wiki.cython.org/enhancements/metaprogramming

Briefly, it allows you to define a transform in the Cython source code. 
  The transform runs at compile time, and takes the *parse trees* of its 
arguments.  In the examples, I define a simple symbolic differentiator
"deriv" which means you can write:

def eggs(a, b):
    return deriv(5*a+b, a)

and it is translated at compile time to:

def eggs(a, b):
    return (((5 * 1) + (0 * a)) + 0)

You can use this, for example, with numerical optimization techniques 
like Newton's method.  An example which differentiates 5 * x**3 - 10 and 
finds it's root is given on the above wiki page, here's the output:

 >>> TestTrans.myfunct(10.0)
(4990.0, 1500.0)
 >>> TestTrans.newtons(TestTrans.myfunct, 10.0)
f( 10.0 ) = 4990.0 , f'( 10.0 ) = 1500.0
f( 6.67333333333 ) = 1475.93037185 , f'( 6.67333333333 ) = 668.000666667
f( 4.46385893383 ) = 434.735082042 , f'( 4.46385893383 ) = 298.890548717
f( 3.00936301916 ) = 126.267956666 , f'( 3.00936301916 ) = 135.843986716
f( 2.07985587115 ) = 34.9852072625 , f'( 2.07985587115 ) = 64.8870066716
f( 1.54068464016 ) = 8.28568621842 , f'( 1.54068464016 ) = 35.6056374064
f( 1.3079774954 ) = 1.18847303518 , f'( 1.3079774954 ) = 25.6620769269
f( 1.26166506953 ) = 0.0415843883547 , f'( 1.26166506953 ) = 23.8769812152
f( 1.25992345957 ) = 5.73769235945e-05 , f'( 1.25992345957 ) = 23.8111068596
f( 1.2599210499 ) = 1.09734443754e-10 , f'( 1.2599210499 ) = 23.8110157797
f( 1.25992104989 ) = 0.0 , f'( 1.25992104989 ) = 23.8110157795
1.2599210498948732

It's also useful for moving computation from run time to compile time, 
and makes it easy for the programmer to specify what should happen where.

There are many other use cases as well.

I'm attaching a patch that implements the examples.  It's very 
proof-of-concept, which means its really rough.  :)  I also implemented 
the bar minimum to get the examples working, but it gives you an idea.

Best,
Martin
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