update from Peter Harris

pep-0309.txt

@@ -1,5 +1,5 @@
 PEP: 309
-Title: Built-in Curry Type
+Title: Function Currying
 Version: $Revision$
 Last-Modified: $Date$
 Author: Peter Harris <scav@blueyonder.co.uk>
@@ -14,13 +14,13 @@ Post-History: 10-Feb-2003, 27-Feb-2003
 Abstract
 ========
 
-This proposal is for a standard curry type for Python that
+This proposal is for a curry constructor for Python that
 allows a new callable to be constructed from a callable and a
 partial argument list (including positional and keyword arguments).
 
 Note: after feedback on comp.lang.python, I am persuaded that the most
-accurate term for this is a 'curry' rather than a 'closure', so the
-terminology has been amended since the first version of this PEP.
+accurate term for this is a 'curry', so the terminology has been
+amended since the first version of this PEP.
 
 I propose a standard library module called "functional", to hold useful
 higher-order functions, including the curry() class.
@@ -40,11 +40,10 @@ In general, languages like that are strongly typed, so the compiler
 always knows the number of arguments expected and can do the right
 thing when presented with a functor and less arguments than expected.
 
-Python has more flexible argument-passing, and so curries cannot be
-implicit in the same way.  Instead of using them, a Python programmer
+Python has more flexible argument-passing, and so function currying cannot
+be implicit in the same way.  Instead, a Python programmer
 will probably either define another named function or use a lambda.
-But lambda syntax is horrible, especially when you want to do
-something complex.
+But lambda syntax is not to everyone's taste, to say the least.
 
 We need something better.
 
@@ -52,22 +51,25 @@ We need something better.
 Rationale
 =========
 
-Here is one way to do a curry in Python::
+Here is one way to do a create a curried callable in Python. The
+implementation below is based on improvements provided by Scott David
+Daniels::
 
     class curry(object):
 
-        def __init__(self, fn, *args, **kw):
-            self.fn, self.args, self.kw = (fn, args, kw)
+        def __init__(*args, **kw):
+            self = args[0]
+            self.fn, self.args, self.kw = (args[1], args[2:], kw)
 
         def __call__(self, *args, **kw):
-            if self.kw:
+            if kw and self.kw:
                 d = self.kw.copy()
                 d.update(kw)
             else:
-                d = kw
+                d = kw or self.kw
             return self.fn(*(self.args + args), **d)
 
-Note that when the curry is called, positional arguments are
+Note that when the curried function is called, positional arguments are
 appended to those provided to the constructor, and keyword arguments
 override and augment those provided to the constructor.
 
@@ -75,8 +77,8 @@ So ``curry(operator.add, 1)`` is a bit like ``(lambda x: 1 + x)``, and
 ``curry(Tkinter.Label, fg='blue')`` is a callable like the Tkinter
 Label class, but with a blue foreground by default.
 
-I think a built-in type called ``curry``, that behaves the same way
-but maybe implemented more efficiently, would be very useful.
+I think a built-in class called ``curry`` that behaves the same way
+would be very useful.
 
 Update: a recipe almost exactly like this has been in the Python
 Cookbook for quite some time, at
@@ -122,7 +124,7 @@ Convenience functions ::
 
     nextarg = sys.argv.pop@(0)
 
-It has not been well-received, so I am not pursuing this as a serious
+It has not been well-received, so I withdraw this part of the
 proposal.
 
 
@@ -201,27 +203,23 @@ I also coded the class in Pyrex::
 
 The performance gain in Pyrex is less than 100% over the nested function
 implementation, since to be fully general it has to operate by Python API
-calls.  Any C implementation will be unlikely to be much faster, so the
-case for a builtin coded in C is not very strong.
-
+calls.  For the same reason, a C implementation will be unlikely to be much
+faster, so the case for a built-in coded in C is not very strong.
 
 
 Summary
 =======
 
-I prefer that curry should be a built-in, with the semantics as
-described, whether as a function or a class. However, it should do its
-apprenticeship in the standard library first.
+I prefer that some means to curry functions should be a built-in, with the
+semantics as described, whether as a function or a callable class. However,
+it should do its apprenticeship in the standard library first.
 
 The standard library module ``functional`` should contain ``curry`` and
 ``rightcurry`` classes, and any other higher-order functions the community
-want. These other functions fall outside this PEP though.
+want. Other functions that might belong there fall outside this PEP though.
 
 The @ syntax proposal is withdrawn.
 
-Since this proposal is now much less ambitious, I'd like to aim for
-inclusion in Python 2.3.
-
 
 Copyright
 =========