[Caml-list] naming parts of optional arguments?

[Caml-list] naming parts of optional arguments?

[Chris Hecker]

Is there a way to name the components of an optional argument?

# let f ((x,y) as xy) = xy;;
val f : 'a * 'b -> 'a * 'b = <fun>
# let f ?xy () = xy;;
val f : ?xy:'a -> unit -> 'a option = <fun>
# let f ?((x,y) as xy) () = xy;;
Characters 8-9:
   let f ?((x,y) as xy) () = xy;;
           ^
Syntax error

Chris

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Re: [Caml-list] naming parts of optional arguments?

[Chris Hecker]

Before someone comments that the optional argument is an 'a option and not 
an 'a, what I really wanted to do is this:

# let f ?(((x,y) as xy) = 0.0,0.0) () = xy;;
Characters 8-9:
   let f ?(((x,y) as xy) = 0.0,0.0) () = xy;;
           ^
Syntax error

Which also doesn't work but there's no 'a option involved, so it 
"should".  I was trying to create the shortest example but took it a bit 
too far.

Chris

At 17:05 3/27/2003 -0800, Chris Hecker wrote:

>Is there a way to name the components of an optional argument?
>
># let f ((x,y) as xy) = xy;;
>val f : 'a * 'b -> 'a * 'b = <fun>
># let f ?xy () = xy;;
>val f : ?xy:'a -> unit -> 'a option = <fun>
># let f ?((x,y) as xy) () = xy;;
>Characters 8-9:
>   let f ?((x,y) as xy) () = xy;;
>           ^
>Syntax error
>
>Chris
>
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Re: [Caml-list] naming parts of optional arguments?

[Max Kirillov]

On Thu, Mar 27, 2003 at 05:05:17PM -0800, Chris Hecker wrote:
> 
> Is there a way to name the components of an optional argument?

# let f ?xy:((x,y)=0,0) () = x+y;; 
val f : ?xy:int * int -> unit -> int = <fun>
# f ();;                           
- : int = 0
# f ~xy:(1,2) ();;
- : int = 3

-- 
Max

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Re: [Caml-list] naming parts of optional arguments?

[Chris Hecker]

James replied off list, but I thought the others might like to see it:

At 17:35 3/27/2003 -0800, james woodyatt wrote:
># let f ?xy:(x,y as xy = 0.0,0.0) () = xy;;
>val f : ?xy:float * float -> unit -> float * float = <fun>

Ah, that's what I wanted, thanks!  It looks like you can just do ?xy:(x,y = 
0,0) and skip the "as xy" too.  Wacky syntax...it looks like I should have 
looked in the pseudo-bnf before posting since it looks like this is in there.

Thanks,
Chris


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Re: [Caml-list] naming parts of optional arguments?

[Chris Hecker]

[old thread resurrected]

Actually, I spoke too soon below, you have to have the "as xy" on there to 
be able to reference the tuple by xy.  Doesn't that seem redundant given 
the ?xy: specification (which doesn't seem to be used)?

# let f ?xy:((x,y)=(0,0)) () = x + y;;
val f : ?xy:int * int -> unit -> int = <fun>
# let f ?xy:((x,y)=(0,0)) () = xy;;
Characters 29-31:
   let f ?xy:((x,y)=(0,0)) () = xy;;
                                ^^
Unbound value xy
# let f ?xy:((x,y) as xy =(0,0)) () = xy;;
val f : ?xy:int * int -> unit -> int * int = <fun>
# let f ?xy:((x,y) as blah =(0,0)) () = blah;;
val f : ?xy:int * int -> unit -> int * int = <fun>
#

Chris



At 18:11 3/27/2003 -0800, Chris Hecker wrote:

>James replied off list, but I thought the others might like to see it:
>
>At 17:35 3/27/2003 -0800, james woodyatt wrote:
>># let f ?xy:(x,y as xy = 0.0,0.0) () = xy;;
>>val f : ?xy:float * float -> unit -> float * float = <fun>
>
>Ah, that's what I wanted, thanks!  It looks like you can just do ?xy:(x,y 
>= 0,0) and skip the "as xy" too.  Wacky syntax...it looks like I should 
>have looked in the pseudo-bnf before posting since it looks like this is 
>in there.
>
>Thanks,
>Chris
>
>
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Re: [Caml-list] naming parts of optional arguments?

[Jacques Garrigue]

From: Chris Hecker <checker@d6.com>
Date: Sun, 27 Jul 2003 20:41:57 -0700

> [old thread resurrected]

Very old indeed.

> Actually, I spoke too soon below, you have to have the "as xy" on there to 
> be able to reference the tuple by xy.  Doesn't that seem redundant given 
> the ?xy: specification (which doesn't seem to be used)?
> 
> # let f ?xy:((x,y)=(0,0)) () = x + y;;
> val f : ?xy:int * int -> unit -> int = <fun>
> # let f ?xy:((x,y)=(0,0)) () = xy;;
> Characters 29-31:
>    let f ?xy:((x,y)=(0,0)) () = xy;;
>                                 ^^
> Unbound value xy
> # let f ?xy:((x,y) as xy =(0,0)) () = xy;;
> val f : ?xy:int * int -> unit -> int * int = <fun>
> # let f ?xy:((x,y) as blah =(0,0)) () = blah;;
> val f : ?xy:int * int -> unit -> int * int = <fun>

No contradiction at all: ?xy: is a label, not a variable name.
If you care about length, you can still write:

  let f ?(xy=(0,0)) () = xy

The distinction between label and variable is useful to avoid masking
the environment.

  let x = ref 3
  let f ?x:(x' = !x + 1) () = x := x'

Jacques Garrigue

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Re: [Caml-list] naming parts of optional arguments?

[Chris Hecker]

>No contradiction at all: ?xy: is a label, not a variable name.

Well, except for in this case, of course, when it is a variable name:

# let f ?xy () = xy;;
val f : ?xy:'a -> unit -> 'a option = <fun>

>If you care about length, you can still write:
>   let f ?(xy=(0,0)) () = xy

No, because I need to break out the parts of the tuple and name the whole 
tuple, which was the point of the thread, so the only way to do that I can 
see is this beautiful expression:

# let f ?xy:((x,y) as xy = 0,0) () = xy,x,y;;
val f : ?xy:int * int -> unit -> (int * int) * int * int = <fun>

All I'm saying is that having the first example above work leads one to 
believe the xy is usable inside the function body in general.

On the whole, the syntax for defining default parameters is nonintuitive 
and inconsistent, because you need the parenthesis sometimes, you need the 
"as xy" sometimes, you need the ?label: sometimes, etc.

Chris

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Re: [Caml-list] naming parts of optional arguments?

[Jacques Garrigue]

From: Chris Hecker <checker@d6.com>
Subject: Re: [Caml-list] naming parts of optional arguments?
Date: Mon, 28 Jul 2003 09:35:15 -0700

> 
> >No contradiction at all: ?xy: is a label, not a variable name.
> 
> Well, except for in this case, of course, when it is a variable name:
> 
> # let f ?xy () = xy;;
> val f : ?xy:'a -> unit -> 'a option = <fun>

Where do you see a ?xy: in the above source code?
?xy is a shorthand for ?xy:xy, as explained in the manual.
xy is the variable, not ?xy:.

Jacques Garrigue

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Re: [Caml-list] naming parts of optional arguments?

[Chris Hecker]

>Where do you see a ?xy: in the above source code?
>?xy is a shorthand for ?xy:xy, as explained in the manual.
>xy is the variable, not ?xy:.

Ah, my mistake.  Although, you must admit, it's pretty subtle.  That still 
doesn't answer why the "as" doesn't work without the label.

Chris

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Re: [Caml-list] naming parts of optional arguments?

[Matt Gushee]

On 27 Mar 2003 at 17:05, Chris Hecker wrote:
 
> Is there a way to name the components of an optional argument?

Are you sure that's what you need to do? Your examples don't show you 
using the x and y values separately.

> # let f ((x,y) as xy) = xy;;
> val f : 'a * 'b -> 'a * 'b = <fun>
> # let f ?xy () = xy;;
> val f : ?xy:'a -> unit -> 'a option = <fun>
> # let f ?((x,y) as xy) () = xy;;
> Characters 8-9:
>    let f ?((x,y) as xy) () = xy;;

At any rate, this works for me:

  # let f ?(xy = 0.0, 0.0) () = xy;;
  val f : ?xy:float * float -> unit -> float * float = <fun>

Now you know xy is a pair of floats, and it's simple to extract the 
separate values if you need to. Or do you need something else that 
I've missed?

-- 
Matt Gushee
Englewood, CO USA

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