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bh=wY7UqlYxxvxecTm4ZXMhfA46hl74lIUzzv9BYJ3373k=; b=hqe4T6XEtD169YKL3lKIu4fUIRWS5f9yA4DzscBZ7KXyCKGWvWybLykNVQjAyzs3P5 QDNjLFNymVQQFV/INjC8RCf7VQ6WcJHfpG5UsQ4E7aQ/E+Yl3o7wxxjth5aT4IkBxzAP mVyvkM2HakoHGKNaNh4xQzdeRW7N9BTtwmX7Bn00edyIJuBQZveIB/xB3lUxfY8dnTKo iNFRVvxmHlolvEYkefxXZjL1R3p//98u8YHUElkOH107GR712vNAF0Y/hoZ9AAFQfR3O kti1/hO4Fn5V5AIQKaG/mnrXwCDIuix3UnRmUeqXKoAgWXaG60SYd863hnVv5VeDSPLb 0ILg== X-Gm-Message-State: AJaThX6HFgwFmMscEOrznosOyCWcRxgx9kV0ySUO9XrOEuUDIEDHtcgV oYyOhGWEqwh7ezT4uphVIsopO4X/6ewfD99DoZw= X-Google-Smtp-Source: ABhQp+RqOpwbv+28evyL7aKhVECKVZijC9xH3f7NSr8Z30l9BDD5rKWNxMl8NAo7cmM8A/QtQTunxhDNF89xezog3pk= X-Received: by 10.157.74.55 with SMTP id h52mr6119641otf.6.1509817971558; Sat, 04 Nov 2017 10:52:51 -0700 (PDT) MIME-Version: 1.0 Received: by 10.157.34.77 with HTTP; Sat, 4 Nov 2017 10:52:30 -0700 (PDT) In-Reply-To: <20171101071609.GA1448@Magus.localnet> References: <20171101071609.GA1448@Magus.localnet> From: Philippe Veber Date: Sat, 4 Nov 2017 18:52:30 +0100 Message-ID: To: Oleg , Philippe Veber , caml users , "Richard W.M. Jones" , nick.palladinos@gmail.com Content-Type: multipart/alternative; boundary="001a114f0512decc77055d2be35e" X-Validation-by: philippe.veber@gmail.com Subject: Re: [Caml-list] What if exn was not an open type? --001a114f0512decc77055d2be35e Content-Type: text/plain; charset="UTF-8" Thanks a lot Leo and Oleg for all this very exciting material! 2017-11-01 8:16 GMT+01:00 Oleg : > > > > I thought one big selling argument of monads was also that the type of > > the functions shows which effect it performs. As I understand it, it > > is not the case for effects, at least not in existing implementations > > like multicore ocaml. ... Also, would you know a reference that shows > > that effects compose indeed a lot more easily than monads? > > How expressive are the types of effectful computations pretty much > depends on a particular type system in use. Let me cite from the message > that I received from Nick Palladinos (CCed) the other week, who implemented > extensible effects in F#, a rather close relative of OCaml. You can > write the code as below > > let example () = > eff { > do! put 1 > let! x = get () > let! y = ask () > return x + y > } > > (Here, `eff' is a tag of so-called computational expressions of F#, a > very handy feature). > > The *inferred* type is as follows > val example : unit -> Eff<'U,int> when 'U :> Reader and 'U :> > State > > clearly stating that example is an effectful expression that uses at > least Reader and State effects. The example also illustrates > composability, your second question: put/get and ask are operations of two > distinct effects (State and Reader, resp). You can combine them freely > within the same program. > > (I hope Nick will write a paper explaining his implementation so that > we can all learn from it.) > > To give more references (in addition to Leo's work), I should point to Koka > https://koka-lang.github.io/koka/doc/kokaspec.html > > which is an OCaml-like language based on effects and > effect-typing. The language is mature enough to write a web server in > it (as Daan Leijen described in his talk at the ML Family workshop > this year). > > Other references are the recent Effekt library in Scala > http://b-studios.de/scala-effekt/ > and extensible-effect library > http://okmij.org/ftp/Haskell/extensible/ > which, although being first proposed for Haskell has also been ported > to Scala (and now F#). Purescript's extensible effects are also > similar. > > > --001a114f0512decc77055d2be35e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Thanks a lot Leo and Oleg for all this very exciting mater= ial!

201= 7-11-01 8:16 GMT+01:00 Oleg <oleg@okmij.org>:


> I thought one big selling argument of monads was also that the type of=
> the functions shows which effect it performs. As I understand it, it > is not the case for effects, at least not in existing implementations<= br> > like multicore ocaml. ... Also, would you know a reference that= shows
> that effects compose indeed a lot more easily than mo= nads?

How expressive are the types of effectful computations pretty much depends on a particular type system in use. Let me cite from the message
that I received from Nick Palladinos (CCed) the other week, who implemented=
extensible effects in F#, a rather close relative of OCaml. You can
write the code as below

let example () =3D
=C2=A0 =C2=A0 eff {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 do! put 1
=C2=A0 =C2=A0 =C2=A0 =C2=A0 let! x =3D get ()
=C2=A0 =C2=A0 =C2=A0 =C2=A0 let! y =3D ask ()
=C2=A0 =C2=A0 =C2=A0 =C2=A0 return x + y
=C2=A0 =C2=A0 }

(Here, `eff' is a tag of so-called computational expressions of F#, a very handy feature).

The *inferred* type is as follows
=C2=A0 val example : unit -> Eff<'U,int> when 'U :> Rea= der<int> and 'U :> State<int>

clearly stating that example is an effectful expression that uses at
least Reader and State effects. The example also illustrates
composability, your second question: put/get and ask are operations of two<= br> distinct effects (State and Reader, resp). You can combine them freely
within the same program.

(I hope Nick will write a paper explaining his implementation so that
we can all learn from it.)

To give more references (in addition to Leo's work), I should point to = Koka
=C2=A0 =C2=A0 =C2=A0 =C2=A0 https://koka-lang.gith= ub.io/koka/doc/kokaspec.html

which is an OCaml-like language based on effects and
effect-typing. The language is mature enough to write a web server in
it (as Daan Leijen described in his talk at the ML Family workshop
this year).

=C2=A0 =C2=A0 =C2=A0 =C2=A0 Other references are the recent Effekt library = in Scala
=C2=A0 =C2=A0 =C2=A0 =C2=A0 http://b-studios.de/scala-effekt/<= /a>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 and extensible-effect library
=C2=A0 =C2=A0 =C2=A0 =C2=A0 http://okmij.org/ftp/Haskell/extensible/
which, although being first proposed for Haskell has also been ported
to Scala (and now F#). Purescript's extensible effects are also
similar.



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