[Python-Dev] thunks

[Guido van Rossum]

I still don't have time to read this thread :-(, but I had a new idea
that I'd like to fly here.

If we want to support thunks that blend into the scope of their
environment as well as thunks that introduce a new local scope, here's
one possible way to do it:

Thunk blending in:

  [<variable> =] <expression>:
    <block>

Thunk introducing a new local scope:

  [<variable> =] <expression> lambda:
     <block>

(Never mind the ugly things I've said about lambda in the past. :-)

I'm confident that the parser can distinguish these, and I'm confident
that the scope blending can be implemented using nested-scope cells.

Adding formal parameters to the second case would go like this:

  [<variable> =] <expression> lambda <arguments>:
     <block>

One concern I have in both cases: I think there are use cases for
wanting more than one block.  Glyph's example wants to define various
callbacks for a remote call, and this would need multiple blocks.  I
think the syntax for this would have to use some kind of keyword-based
continuation, e.g.

  [<variable> =] <expression> lambda:
    <block>
  and <expression> lambda:
    <block>
  ...

Disclaimer: this is a half-baked idea.

--Guido van Rossum (home page: http://www.python.org/~guido/)