[Python-ideas] Backtick expression: similar to a shorter lambda syntax

[Bruce Leban]

On Sun, Jan 20, 2019 at 6:43 PM James Lu <jamtlu at gmail.com> wrote:

> Backtick expressions work exactly like lambdas, except that they are bound
> to the instance they are created in every time that class is used to create
> one. To illustrate, ...


First, if there is a useful procedure I am strongly against using backticks
because (1) it's been used in the past with an entirely different meaning
and (2) it looks ugly and is not visually suggestive at all of what it
does, especially not the subtle difference between other function
definitions.

Second, I don't understand exactly what this difference or why it would be
useful. It would help for you to give examples comparing lambda and this
variation.

Third, you mention using ^ in "explicit" expressions to refer to parameters
of the "created function" and I do not know what function you are referring
to or what the exact semantics of this are. Again, a comparison of two
expressions with and without that ^ would help. An expression is not a
function and not all expressions are written inside functions. (And as to
the specific proposed syntax, there already is the ^ xor operator and the
most expected meaning of ^value is ~value. just as the unary + and -
operators corresponds to the binary operators.

The only thing that I can think of is that you want `foo + ^bar` to be
another way of writing lambda bar: foo + bar with some under-specified behavior
for evaluating foo and different under-specified behavior for evaluating bar
.

Finally, if there is some other useful semantics for references inside a
function definition, then I would think the best way to do that is to
implement that, not add a new function difference. For example,

lambda foo: foo + $bar

def sample(foo):

    return foo + $foo


where I'm arbitrarily using $ to represent the new semantics whatever they
are (no point in bikeshedding syntax when semantics are yet to be defined).

--- Bruce
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