[Python-3000] 'defop' syntax with no new keywords (original) (raw)

Talin talin at acm.org
Fri Dec 8 11:15:19 CET 2006

Another mini-brainstorm, which is how to represent PJE's 'defop' syntax without adding any keywords:

Alternative 1. Omitting the function name in 'def' statements.

Let us define the behavior of the 'def' statement as follows:

The function name in the 'def' statement is optional - if the

function name is absent, then def behaves exactly as it does now, except that the assignment of the function object to the symbol name is skipped. In particular, any function decorators are still invoked, however the result of those decorators are thrown away.

So to overload the 'len' operator:

class Foo:

@overload(len): def (self): ... compute len( self ) ...

The idea here is that it's up to the decorator to store the function object somewhere - we don't automatically store it if there's no function name supplied.

In this example, the argument to the 'overload' decorator is a reference to the global 'len' generic function. The 'overload' in this case takes the reference to the resulting function and adds it as a method to 'len'. The decorator can extract the type of the function's enclosing class from the various attributes of the function object (i.e. the function still knows what class defined it.)

The expression 'def (args)' is a no-op unless there are decorators.

Alternative 2: Function name in parens:

In a def statement, putting the name of the function in parentheses indicates that the function name is an expression rather than a symbol:

@overload def (len)(self): ...

Decorators that are used in this fashion should expect two arguments rather than one, which are the name-expression and the function object.

-- Talin

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