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[Caml-list] naming parts of optional arguments?
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 Date: -- (:) From: Jacques Garrigue Subject: Re: [Caml-list] naming parts of optional arguments?
```From: Chris Hecker <checker@d6.com>
Date: Sun, 27 Jul 2003 20:41:57 -0700

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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