On Wed, Dec 01, 2021 at 12:26:33PM +0000, Matt del Valle wrote:
Steven gave the following example of a function signature that would be difficult to visually parse if this proposal and arrow lambdas were accepted:
And while I agree that it does sort of stop you in your tracks when you see this, I think there are a couple of reasons why this is not as big of a problem as it appears.
I totally agree with you that, for even moderately experienced Pythonistas, it is possible to parse that. It's not literally ambiguous syntax that cannot be resolved. I am confident that the parser will be able to work it out just fine :-)
I care more about the poor reader who may not be a moderately experienced Pythonista, and will be trying to work out why there are two different arrow symbols with four different meanings:
* function return annotation * typing.Callable type annotation * lambda alternative syntax * late-bound defaults
I'm sure that people will learn the many uses of the arrow symbols. After all, people learn Perl and APL :-) Closer to home, we also learn all the many different uses of the star symbol `*`.
Yes, spaces will help the reader *parse* the pieces of the function signature. But spaces doesn't help the reader decipher and remember the different meanings of the arrows. Also the use of extra spaces goes against the usual style guides that we *don't* use spaces between the colon and the annotation, or the equals sign and the default.
For the sake of discussion, I've been using Chris' arrow symbol, but that doesn't mean I've warmed to it. Aside from the other issues, it is the wrong way around:
parameter => expression
implies moving the parameter into the expression, which is the wrong way around. The expression moves into the parameter.
E.g. in R, you can write assignment with an equals sign, or an arrow, but the arrow points from the value to the variable:
> x <- 1 > 2 -> y > c(x, y)  1 2
I've never seen a language or pseudo-code that does assignment with the arrow pointing from the variable to the value. Does anyone know of any?