* [Caml-list] polymorphic parameters
@ 2012-09-06 9:20 Dan Bensen
2012-09-06 9:35 ` Philippe Wang
0 siblings, 1 reply; 6+ messages in thread
From: Dan Bensen @ 2012-09-06 9:20 UTC (permalink / raw)
To: caml-list
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How do you indicate that a function parameter is a polymorphic function?
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Caml-list] polymorphic parameters
2012-09-06 9:20 [Caml-list] polymorphic parameters Dan Bensen
@ 2012-09-06 9:35 ` Philippe Wang
2012-09-06 9:49 ` David House
2012-09-06 9:55 ` Gabriel Scherer
0 siblings, 2 replies; 6+ messages in thread
From: Philippe Wang @ 2012-09-06 9:35 UTC (permalink / raw)
To: Dan Bensen; +Cc: caml-list
On Thu, Sep 6, 2012 at 11:20 AM, Dan Bensen <danbensen@att.net> wrote:
> How do you indicate that a function parameter is a polymorphic function?
I hope these 2 lines will answer your question:
let f g x = g x
let f (g: 'a -> 'b) x = g x
--
Philippe Wang
mail@philippewang.info
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Caml-list] polymorphic parameters
2012-09-06 9:35 ` Philippe Wang
@ 2012-09-06 9:49 ` David House
2012-09-06 13:19 ` Philippe Wang
2012-09-06 9:55 ` Gabriel Scherer
1 sibling, 1 reply; 6+ messages in thread
From: David House @ 2012-09-06 9:49 UTC (permalink / raw)
To: Philippe Wang; +Cc: Dan Bensen, caml-list
Careful: that doesn't actually ensure polymorphism. See:
https://ocaml.janestreet.com/?q=node/79
On Thu, Sep 6, 2012 at 10:35 AM, Philippe Wang <mail@philippewang.info> wrote:
> On Thu, Sep 6, 2012 at 11:20 AM, Dan Bensen <danbensen@att.net> wrote:
>> How do you indicate that a function parameter is a polymorphic function?
>
> I hope these 2 lines will answer your question:
>
> let f g x = g x
>
> let f (g: 'a -> 'b) x = g x
>
> --
> Philippe Wang
> mail@philippewang.info
>
> --
> Caml-list mailing list. Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Caml-list] polymorphic parameters
2012-09-06 9:35 ` Philippe Wang
2012-09-06 9:49 ` David House
@ 2012-09-06 9:55 ` Gabriel Scherer
2012-09-06 9:59 ` Gabriel Scherer
1 sibling, 1 reply; 6+ messages in thread
From: Gabriel Scherer @ 2012-09-06 9:55 UTC (permalink / raw)
To: Philippe Wang; +Cc: Dan Bensen, caml-list
Philippe, the function parameter is not really polymorphic in your
example: it's the whole function type that is.
`f` is given the type (('a -> 'b) -> 'a -> 'b) by the OCaml
type-checker, but this is syntactic sugar for (forall 'a 'b. ('a ->
'b) -> 'a -> 'b).
Note how the universal quantifiers are at the beginning of the type,
and not inside the function parameter.
One could expect to be able to express the type forall 'a . (forall 'b
. 'a -> 'b) -> 'a -> int for example.
See the following FAQ item for a short answer to this question:
http://caml.inria.fr/resources/doc/faq/core.en.html#polymorphic-arguments
On Thu, Sep 6, 2012 at 11:35 AM, Philippe Wang <mail@philippewang.info> wrote:
> On Thu, Sep 6, 2012 at 11:20 AM, Dan Bensen <danbensen@att.net> wrote:
>> How do you indicate that a function parameter is a polymorphic function?
>
> I hope these 2 lines will answer your question:
>
> let f g x = g x
>
> let f (g: 'a -> 'b) x = g x
>
> --
> Philippe Wang
> mail@philippewang.info
>
> --
> Caml-list mailing list. Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Caml-list] polymorphic parameters
2012-09-06 9:55 ` Gabriel Scherer
@ 2012-09-06 9:59 ` Gabriel Scherer
0 siblings, 0 replies; 6+ messages in thread
From: Gabriel Scherer @ 2012-09-06 9:59 UTC (permalink / raw)
To: Philippe Wang; +Cc: Dan Bensen, caml-list
PS: the use of the wording "syntactic sugar" here is inappropriate:
"forall 'a ..." is not valid OCaml syntax. I meant that the formal
type this notation is referring to is quantified in this way. For
concrete syntax to denote polymorphism, ('a . foo) is used by
polymorphic field and methods or polymorphic recursion, and the blog
post David House linked discusses another syntax -- and there is yet
something different, a fusion of these two, for GADTs; unfortunately
this aspect of OCaml syntax is getting a bit crowded.
On Thu, Sep 6, 2012 at 11:55 AM, Gabriel Scherer
<gabriel.scherer@gmail.com> wrote:
> Philippe, the function parameter is not really polymorphic in your
> example: it's the whole function type that is.
> `f` is given the type (('a -> 'b) -> 'a -> 'b) by the OCaml
> type-checker, but this is syntactic sugar for (forall 'a 'b. ('a ->
> 'b) -> 'a -> 'b).
>
> Note how the universal quantifiers are at the beginning of the type,
> and not inside the function parameter.
> One could expect to be able to express the type forall 'a . (forall 'b
> . 'a -> 'b) -> 'a -> int for example.
>
> See the following FAQ item for a short answer to this question:
> http://caml.inria.fr/resources/doc/faq/core.en.html#polymorphic-arguments
>
> On Thu, Sep 6, 2012 at 11:35 AM, Philippe Wang <mail@philippewang.info> wrote:
>> On Thu, Sep 6, 2012 at 11:20 AM, Dan Bensen <danbensen@att.net> wrote:
>>> How do you indicate that a function parameter is a polymorphic function?
>>
>> I hope these 2 lines will answer your question:
>>
>> let f g x = g x
>>
>> let f (g: 'a -> 'b) x = g x
>>
>> --
>> Philippe Wang
>> mail@philippewang.info
>>
>> --
>> Caml-list mailing list. Subscription management and archives:
>> https://sympa-roc.inria.fr/wws/info/caml-list
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Caml-list] polymorphic parameters
2012-09-06 9:49 ` David House
@ 2012-09-06 13:19 ` Philippe Wang
0 siblings, 0 replies; 6+ messages in thread
From: Philippe Wang @ 2012-09-06 13:19 UTC (permalink / raw)
To: David House; +Cc: Dan Bensen, caml-list
You're right, I misread the question!
(I missed one word, which changed the semantics of the question)
On Thu, Sep 6, 2012 at 11:49 AM, David House <dhouse@janestreet.com> wrote:
> Careful: that doesn't actually ensure polymorphism. See:
>
> https://ocaml.janestreet.com/?q=node/79
>
> On Thu, Sep 6, 2012 at 10:35 AM, Philippe Wang <mail@philippewang.info> wrote:
>> On Thu, Sep 6, 2012 at 11:20 AM, Dan Bensen <danbensen@att.net> wrote:
>>> How do you indicate that a function parameter is a polymorphic function?
>>
>> I hope these 2 lines will answer your question:
>>
>> let f g x = g x
>>
>> let f (g: 'a -> 'b) x = g x
>>
>> --
>> Philippe Wang
>> mail@philippewang.info
>>
>> --
>> Caml-list mailing list. Subscription management and archives:
>> https://sympa-roc.inria.fr/wws/info/caml-list
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>>
--
Philippe Wang
mail@philippewang.info
^ permalink raw reply [flat|nested] 6+ messages in thread
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2012-09-06 9:20 [Caml-list] polymorphic parameters Dan Bensen
2012-09-06 9:35 ` Philippe Wang
2012-09-06 9:49 ` David House
2012-09-06 13:19 ` Philippe Wang
2012-09-06 9:55 ` Gabriel Scherer
2012-09-06 9:59 ` Gabriel Scherer
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