[Python-ideas] And now for something completely different
jjb5 at cornell.edu
Fri Sep 19 21:46:23 CEST 2008
Cliff Wells wrote:
> So... now, here's my shiny new idea: lazy evaluation of function
> arguments (by some explicit syntactical indicator). Arguments would not
> be evaluated until they are encountered *at runtime* in the function
> body. They could be compiled, but not evaluated.
This is called "pass by name":
Syntactically you need some parameter annotation that says you want
pass-by-name semantics, then add a "thunk" layer when those parameters
are used in the code.
Note that in languages that support pass-by-name, I happen to be
familiar with ALGOL, it operates on both the left and right hand side of
assignment statements. Perhaps something like this:
>>> def foo(arg : __byname__):
... print arg
... arg = (arg * 3) + 1
... print arg
>>> x = 2
>>> print x
> I think this would have appeal outside of my particular desire (lazy
> evaluation is a useful feature in-and-of itself) but would also solve my
> particular issue (I could implement functional versions of any control
> structure I like, and even implement new ones).
I'm with you, I think there are quite effective uses for this
functionality, but nothing that will combat the wave of "why this is
fundamentally wrong" or "there's a better way to do it" arguments.
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