Re: Why does for(x <- c; y = ...) yield {...} become c.map(x => (x, ...)).map((x,y) => {...})

Just to have functoriality? (Otoh, unit and flatmap provide it)
On Jan 24, 2015 11:07 AM, "Haoyi Li" <[email protected]> wrote:

> I've been looking at http://docs.scala-lang.org/tutorials/FAQ/yield.html,
> and found this
>
> for(x <- c; y = ...) yield {...}
>
> is translated into
>
> c.map(x => (x, ...)).map((x,y) => {...})
>
>
> This seems rather odd to me. Why not
>
> for(x <- c; y = ...) yield {...}
>
> is translated into
>
> c.flatMap{ x => val y = ...; {...} }
>
>
> Isn't this basically the same, but much more straightforward?
>
> The reason I bumped into this is that I was trying to implement a bunch of
> custom for-comprehension generators, and it kept asking for *.map*, and I
> couldn't figure out why. These were pretty odd generators, e.g. a TryCatch
> generator which you can put anywhere in your loop and which propagates a
> Seq() back up if it catches an exception, and so don't really have
> meaningful values to pass into *map* or *flatMap*s.
>
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