On 07/12/13 20:55, Simon Sapin wrote:
On 07/12/2013 01:14, Huon Wilson wrote:
I personally think a better solution is something like Haskell's do
notation[1], where you can chain several computations that return
Option<..> such that if any intermediate one returns None, the later
ones are not evaluated and the whole expression returns None, which
saves having to call .get()/.unwrap()/.expect() a lot.
We have that, it’s Option’s .and_then() method.
This can work for types like Result too (in fact, the Haskell
implementation of `do` is sugar around some monad functions, so any
monad can be used there; we currently don't have the power to express
the monad typeclass/trait in Rust so the fully general form probably
isn't possible as a syntax extension yet, although a limited version
is).
Yes, that's what my syntax extension[1] (to which Ziad alludes)
desugared to (well, the former name, .chain).
However, even something simple like `foo.and_then(|x| bar.and_then(|y|
baz.map(|z| x + y + z)))` is significantly worse than
do
x <- foo
y <- bar
z <- baz
return $ x + y + z
as it is in Haskell. And more complicated examples with additional
within the closures are significantly worse for the .and_then form
(leading to pyramids of doom, and Rust already has enough of those).
Huon
[1]: https://mail.mozilla.org/pipermail/rust-dev/2013-May/004182.html
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