

Elm 0.15: Asynchrony with Tasks - jwmerrill
http://elm-lang.org/blog/announce/0.15.elm

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taylorfausak
The decisions the Elm team make continue to impress me. I like that they are
willing to break from tradition in order to create a better programming
environment. In particular, changing the head function to be total is a great
move.

    
    
        head : List a -> Maybe a
    

Compare that with the same function in Haskell.

    
    
        head :: [a] -> a
    

To me, the Elm version makes more sense. (It also avoids having to explain
that "[a]" means "list of 'a's".)

~~~
lisperforlife
In addition to the lexical change, the result now returns a Maybe instead of
the actual element. This was done to avoid runtime crashes when head
encounters an empty list. However, this means that everytime you have to use
head, you will have to pattern match on Just x/Nothing to consume it. However,
you can still use the (x::xs) pattern matching syntax to obtain head and tail
and pattern match on [] for empty lists.

Absence of applicatives or monads mean that you have to explicitly pattern
match on Just/Nothing everytime. There is a proposal to add `?` as an operator
to obtain the head of the list without the Maybe and provide a default value
if it is Nothing. Also there is another proposal to allow `unsafe` for the
program to crash if the result is Nothing.

~~~
dragonwriter
> Absence of applicatives or monads mean that you have to explicitly pattern
> match on Just/Nothing everytime.

It seems to me that most real uses can probably be solved by map, and
withDefault if you really need to get out of the Maybe monad for some reason
(though map should make it so that you don't have to for most things.)

> There is a proposal to add `?` as an operator to obtain the head of the list
> without the Maybe and provide a default value if it is Nothing.

Since elm supports user-defined operators, can't you just do that yourself.
Something like:

    
    
      list ? default = withDefault default (head list)

~~~
rtfeldman
Yep! The proposal is to add that to the core libraries, and is basically just
waiting to see how much people actually want to use withDefault that way in
practice.

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thomasweiser
Release of new version of Elm (A functional reactive language for interactive
applications)

"This release introduces tasks, a way to define complex asynchronous
operations. Similar to C#’s tasks and JavaScript’s promises, tasks make it
simple to describe long-running effects and keep things responsive. They also
provide a way to wrap up tons of browser APIs in Elm."

~~~
rudi-c
This is awesome. Dealing with HTTP requests used to be a pain since they were
all signals even when they were used only once, which was not intuitive. This
should make the language much more usable.

~~~
nijiko
I prefer the backcalls of LiveScript to any implementation I have seen thus
far, coupled with do, you can do some pretty complex things

~~~
johnpmayer
There's probably going to be something like do-notation in Elm 0.16.

------
kailuowang
Congratulations to the Elm team! As a side note scala-js provides an
interesting alternative. In the new Principles of Reactive Programming,
[https://class.coursera.org/reactive-002/assignment](https://class.coursera.org/reactive-002/assignment),
a decent RFP example using scalajs was given.

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habitue
Who isn't a fan of Elm? This language keeps impressing me.

~~~
toomim
Lots of people don't get it, and thus aren't fans.

It seems like lots of people in the functional community are fans.

I spent some time trying to get it, and I got part of it, but I'm not yet a
fan.

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moomin
Elm is lovely, but it really needs typeclasses.

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ams6110
That page is really tough to read on a phone.

