extend ComputationExpression builders with Map : m<'a> * ('a -> 'b) -> m<'b>

[baronfel]

Submitted by Georg Haaser on 1/31/2016 12:00:00 AM
8 votes on UserVoice prior to migration

In many scenarios computation expressions could be executed way more efficiently when having just a little more information. The typical use-case for that would be something like

    async {
        let! a = something
        return 2*a
    }

which currently gets translated to:

    async.Bind(something, fun a -> async.Return(2*a))

By monad laws (borrowed from haskell here) this must be equal to:

    async.Map(something, fun a -> 2*a)

In many scenarios the latter can be implemented with a lot less overhead, so in my opinion it would be profitable to allow users to provide this "shortcut".

Original UserVoice Submission
Archived Uservoice Comments

[dsyme]

Going over old issues: just to say that I agree this is a reasonable suggestion.

[rmunn]

Just a note that the conversion from UserVoice glitched on this issue: the two occurrences of 2_a in the sample code should have both been 2*a. There's no special meaning attached to the underscore here; the intended sample code is just "multiply a by 2".

[dsyme]

@rmunn Thanks, fixed.

[Rickasaurus]

Yes please. This is partly why the continuation monad is so crazy expensive right?

[jwosty]

@dsyme needs-rfc tag can be removed