Re: A possible alternative to dot notation for record access
6 even: foo :: (Maybe :: * -> *) Foo -> Bar foo (fromMaybe def -> x) = \x -> case x of Foo x -> x->y->z On Mon, Jul 1, 2013 at 4:27 PM, John Wiegley wrote: > > Edward Kmett writes: > > > If you really want to hunt for unused syntax and we wind up needing a (.) > > analogue then (->) is currently a reserved operator, so opening it up for > > use at the term level could be made to work, and there is a precedent > with > > c/c++ pointer dereferencing. > > Imagine this possible code: > > foo :: Maybe Foo -> Bar > foo (fromMaybe def -> x) = \x -> case x of > Foo x -> x->y->z > > I think it might get a bit ugly to give it a 5th meaning. > > -- > John Wiegley > FP Complete Haskell tools, training and consulting > http://fpcomplete.com johnw on #haskell/irc.freenode.net > > ___ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: A possible alternative to dot notation for record access
Sure. I'd rather have nothing, but at least unlike the (.) proposals it doesn't break existing code. That said I don't think we need either. On Jul 1, 2013, at 2:27 AM, "John Wiegley" wrote: >> Edward Kmett writes: > >> If you really want to hunt for unused syntax and we wind up needing a (.) >> analogue then (->) is currently a reserved operator, so opening it up for >> use at the term level could be made to work, and there is a precedent with >> c/c++ pointer dereferencing. > > Imagine this possible code: > >foo :: Maybe Foo -> Bar >foo (fromMaybe def -> x) = \x -> case x of >Foo x -> x->y->z > > I think it might get a bit ugly to give it a 5th meaning. > > -- > John Wiegley > FP Complete Haskell tools, training and consulting > http://fpcomplete.com johnw on #haskell/irc.freenode.net > > ___ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: A possible alternative to dot notation for record access
> Edward Kmett writes: > If you really want to hunt for unused syntax and we wind up needing a (.) > analogue then (->) is currently a reserved operator, so opening it up for > use at the term level could be made to work, and there is a precedent with > c/c++ pointer dereferencing. Imagine this possible code: foo :: Maybe Foo -> Bar foo (fromMaybe def -> x) = \x -> case x of Foo x -> x->y->z I think it might get a bit ugly to give it a 5th meaning. -- John Wiegley FP Complete Haskell tools, training and consulting http://fpcomplete.com johnw on #haskell/irc.freenode.net ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: A possible alternative to dot notation for record access
If you really want to hunt for unused syntax and we wind up needing a (.)
analogue then (->) is currently a reserved operator, so opening it up for
use at the term level could be made to work, and there is a precedent with
c/c++ pointer dereferencing.
-Edward
On Mon, Jul 1, 2013 at 1:10 AM, Edward Kmett wrote:
> (#) is a legal operator today and is used in a number of libraries.
>
>
> On Sun, Jun 30, 2013 at 11:38 PM, wrote:
>
>> As long as we're bikeshedding...
>>
>> Possibly '#' is unused syntax -- Erlang uses it for its records too, so
>> we wouldn't be pulling it out of thin air. E.g. "person#firstName"
>>
>> Tom
>>
>>
>> El Jun 30, 2013, a las 22:59, AntC
>> escribió:
>>
>> >> Carter Schonwald gmail.com> writes:
>> >>
>> >> indeed, this relates / augments record puns syntax already in
>> > GHC http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-
>> > extns.html#record-puns.
>> >
>> > Uh-oh. That documentation gives an example, and it exactly explains the
>> > weird type-level error I got when I tried to use the proposed syntax
>> > myself:
>> >
>> >Note that:
>> >
>> >* Record punning can also be used in an expression, writing, for
>> > example,
>> >
>> >let a = 1 in C {a}-- !!!
>> >
>> >instead of
>> >
>> >let a = 1 in C {a = a}
>> >
>> >The expansion is purely syntactic, so the expanded right-hand
>> side
>> > expression refers to the nearest enclosing variable that is spelled the
>> > same as the field name.
>> >
>> > IOW the proposal _does_ conflict with existing syntax. (And I guess I
>> can
>> > see a use for the example. Note that outside of that let binding, `a`
>> > would be a field selector function generated from the data decl in which
>> > field `a` appears -- that's the weirdity I got.)
>> >
>> > I suppose the existing syntax has a data constructor in front of the
>> > braces, whereas the proposal wants a term. But of course a data
>> > constructor is a term.
>> >
>> > So the proposal would be a breaking change. Rats! Is anybody using that
>> > feature?
>> >
>> >>
>> >> On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
>> > gmail.com> wrote:
>> >>
>> >> Unlike dot notation, this is unambiguous and doesn't conflict with any
>> > existing syntax (AFAIK). ...
>> >
>> >
>> > ___
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>> > Glasgow-haskell-users@haskell.org
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>>
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>>
>
>
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Re: A possible alternative to dot notation for record access
(#) is a legal operator today and is used in a number of libraries.
On Sun, Jun 30, 2013 at 11:38 PM, wrote:
> As long as we're bikeshedding...
>
> Possibly '#' is unused syntax -- Erlang uses it for its records too, so we
> wouldn't be pulling it out of thin air. E.g. "person#firstName"
>
> Tom
>
>
> El Jun 30, 2013, a las 22:59, AntC
> escribió:
>
> >> Carter Schonwald gmail.com> writes:
> >>
> >> indeed, this relates / augments record puns syntax already in
> > GHC http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-
> > extns.html#record-puns.
> >
> > Uh-oh. That documentation gives an example, and it exactly explains the
> > weird type-level error I got when I tried to use the proposed syntax
> > myself:
> >
> >Note that:
> >
> >* Record punning can also be used in an expression, writing, for
> > example,
> >
> >let a = 1 in C {a}-- !!!
> >
> >instead of
> >
> >let a = 1 in C {a = a}
> >
> >The expansion is purely syntactic, so the expanded right-hand side
> > expression refers to the nearest enclosing variable that is spelled the
> > same as the field name.
> >
> > IOW the proposal _does_ conflict with existing syntax. (And I guess I can
> > see a use for the example. Note that outside of that let binding, `a`
> > would be a field selector function generated from the data decl in which
> > field `a` appears -- that's the weirdity I got.)
> >
> > I suppose the existing syntax has a data constructor in front of the
> > braces, whereas the proposal wants a term. But of course a data
> > constructor is a term.
> >
> > So the proposal would be a breaking change. Rats! Is anybody using that
> > feature?
> >
> >>
> >> On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
> > gmail.com> wrote:
> >>
> >> Unlike dot notation, this is unambiguous and doesn't conflict with any
> > existing syntax (AFAIK). ...
> >
> >
> > ___
> > Glasgow-haskell-users mailing list
> > Glasgow-haskell-users@haskell.org
> > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
> ___
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> Glasgow-haskell-users@haskell.org
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Re: A possible alternative to dot notation for record access
As long as we're bikeshedding...
Possibly '#' is unused syntax -- Erlang uses it for its records too, so we
wouldn't be pulling it out of thin air. E.g. "person#firstName"
Tom
El Jun 30, 2013, a las 22:59, AntC escribió:
>> Carter Schonwald gmail.com> writes:
>>
>> indeed, this relates / augments record puns syntax already in
> GHC http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-
> extns.html#record-puns.
>
> Uh-oh. That documentation gives an example, and it exactly explains the
> weird type-level error I got when I tried to use the proposed syntax
> myself:
>
>Note that:
>
>* Record punning can also be used in an expression, writing, for
> example,
>
>let a = 1 in C {a}-- !!!
>
>instead of
>
>let a = 1 in C {a = a}
>
>The expansion is purely syntactic, so the expanded right-hand side
> expression refers to the nearest enclosing variable that is spelled the
> same as the field name.
>
> IOW the proposal _does_ conflict with existing syntax. (And I guess I can
> see a use for the example. Note that outside of that let binding, `a`
> would be a field selector function generated from the data decl in which
> field `a` appears -- that's the weirdity I got.)
>
> I suppose the existing syntax has a data constructor in front of the
> braces, whereas the proposal wants a term. But of course a data
> constructor is a term.
>
> So the proposal would be a breaking change. Rats! Is anybody using that
> feature?
>
>>
>> On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
> gmail.com> wrote:
>>
>> Unlike dot notation, this is unambiguous and doesn't conflict with any
> existing syntax (AFAIK). ...
>
>
> ___
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users@haskell.org
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
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Re: A possible alternative to dot notation for record access
> Carter Schonwald gmail.com> writes:
>
> indeed, this relates / augments record puns syntax already in
GHC http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-
extns.html#record-puns.
>
Uh-oh. That documentation gives an example, and it exactly explains the
weird type-level error I got when I tried to use the proposed syntax
myself:
Note that:
* Record punning can also be used in an expression, writing, for
example,
let a = 1 in C {a}-- !!!
instead of
let a = 1 in C {a = a}
The expansion is purely syntactic, so the expanded right-hand side
expression refers to the nearest enclosing variable that is spelled the
same as the field name.
IOW the proposal _does_ conflict with existing syntax. (And I guess I can
see a use for the example. Note that outside of that let binding, `a`
would be a field selector function generated from the data decl in which
field `a` appears -- that's the weirdity I got.)
I suppose the existing syntax has a data constructor in front of the
braces, whereas the proposal wants a term. But of course a data
constructor is a term.
So the proposal would be a breaking change. Rats! Is anybody using that
feature?
>
> On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
gmail.com> wrote:
>
> Unlike dot notation, this is unambiguous and doesn't conflict with any
existing syntax (AFAIK). ...
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Re: A possible alternative to dot notation for record access
Judah Jacobson wrote:
> I had a quick idea about record field syntax as specified in the GSoC
> project plan:
>
http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/Plan
> .
>
> Instead of "f.x" (to access field x of record f), maybe we could write
> "f{x}" as the record selection. That is, we'd reuse the brace notation
> which is already in place for record updates. Unlike dot notation, this
is
> unambiguous and doesn't conflict with any existing syntax (AFAIK). It
> would also generalize to "f{x}{y}{z}" instead of "f.x.y.z".
>
> This proposal would add two new forms of expressions:
>
> f{x} to access field x of data f
> ({x}) = \f -> f{x} as a field access section
>
> Additionally, it seems like record mutation expressions could also have
> sections:
>
> ({x=2}) = \f -> f{x=2}
>
> That actually seems useful by itself, regardless of whether we use dot
> notation for field access.
I think this is a pretty nice idea. (Disclaimer: I haven't spent any time on
checking corner cases; also I firmly belong to the anti-further-overloading-
of-dot faction). In any case it is light-weight enough to be actually
useful, it is readable and suggestive, and (at least conceptually) fits well
in the existing record syntax.
This deserves a fully fleshed-out proposal for Haskell' IMO.
Cheers
--
Ben Franksen
() ascii ribbon campaign - against html e-mail
/\ www.asciiribbon.org - against proprietary attachm€nts
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Re: A possible alternative to dot notation for record access
* Carter Schonwald [2013-06-30 03:26:22-0400]
> Otoh, would there be any ambiguity wrt applying functions to blocks?
>
> eg
> f = (+ 1)
> h= f {let x = 7 in 3*x},
> would that trip up the syntax?
This is not valid Haskell anyway (there's no such thing as "applying
functions to blocks"). You can write
h = f (let {x = 7} in 3*x)
or
h = f $ let {x = 7} in 3*x
Roman
> On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
> wrote:
>
> > Hi all,
> >
> > I had a quick idea about record field syntax as specified in the GSoC
> > project plan:
> > http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/Plan
> > .
> >
> > Instead of "f.x" (to access field x of record f), maybe we could write
> > "f{x}" as the record selection. That is, we'd reuse the brace notation
> > which is already in place for record updates. Unlike dot notation, this is
> > unambiguous and doesn't conflict with any existing syntax (AFAIK). It
> > would also generalize to "f{x}{y}{z}" instead of "f.x.y.z".
> >
> > This proposal would add two new forms of expressions:
> >
> > f{x} to access field x of data f
> > ({x}) = \f -> f{x} as a field access section
> >
> > Additionally, it seems like record mutation expressions could also have
> > sections:
> >
> > ({x=2}) = \f -> f{x=2}
> >
> > That actually seems useful by itself, regardless of whether we use dot
> > notation for field access.
> >
> > Best,
> > -Judah
> >
> > ___
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> > Glasgow-haskell-users@haskell.org
> > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
> >
> >
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Re: A possible alternative to dot notation for record access
indeed, this relates / augments record puns syntax already in GHC
http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#record-puns
.
Otoh, would there be any ambiguity wrt applying functions to blocks?
eg
f = (+ 1)
h= f {let x = 7 in 3*x},
would that trip up the syntax?
On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson wrote:
> Hi all,
>
> I had a quick idea about record field syntax as specified in the GSoC
> project plan:
> http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/Plan
> .
>
> Instead of "f.x" (to access field x of record f), maybe we could write
> "f{x}" as the record selection. That is, we'd reuse the brace notation
> which is already in place for record updates. Unlike dot notation, this is
> unambiguous and doesn't conflict with any existing syntax (AFAIK). It
> would also generalize to "f{x}{y}{z}" instead of "f.x.y.z".
>
> This proposal would add two new forms of expressions:
>
> f{x} to access field x of data f
> ({x}) = \f -> f{x} as a field access section
>
> Additionally, it seems like record mutation expressions could also have
> sections:
>
> ({x=2}) = \f -> f{x=2}
>
> That actually seems useful by itself, regardless of whether we use dot
> notation for field access.
>
> Best,
> -Judah
>
> ___
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users@haskell.org
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
>
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