[Caml-list] [Q] explicit typing again

[Caml-list] [Q] explicit typing again

[fis]

hi,

sorry, but i am really enthusiastic about explicit typing.  i will
probably start to annotate expressions like "3" soon...  (-:

could anybody tell me how i get this one straight?

# let (a: int, b) = (1, 3) in a;;
# let (a, b) : int * int = (1, 3) in a;;

thanks a lot,
matthias

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Re: [Caml-list] [Q] explicit typing again

[Jacques Garrigue]

From: fis@wiwi.hu-berlin.de
> could anybody tell me how i get this one straight?
> 
> # let (a: int, b) = (1, 3) in a;;
> # let (a, b) : int * int = (1, 3) in a;;

# let (a : int), b = (1,3) in a;;
# let (a, b : int * int) = (1,3) in a;;

Pairs do not need parentheses.
Type annotations do (except when defining a single value).

Jacques Garrigue

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Re: [Caml-list] [Q] explicit typing again

[Remi Vanicat]

fis@wiwi.hu-berlin.de writes:

> hi,
>
> sorry, but i am really enthusiastic about explicit typing.  i will
> probably start to annotate expressions like "3" soon...  (-:
>
> could anybody tell me how i get this one straight?
>
> # let (a: int, b) = (1, 3) in a;;

it is  :

let ((a:int),b) = (1, 3) in a;;

> # let (a, b) : int * int = (1, 3) in a;;

there it is :
let ((a, b) : int * int) = (1, 3) in a;;

In fact, often it is enough to add some parenthesis around the
"value : type" to make the parser happy.



-- 
Rémi Vanicat

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Re: [Caml-list] [Q] explicit typing again

[Martin Jambon]

On Mon, 29 Mar 2004 fis@wiwi.hu-berlin.de wrote:

> hi,
>
> sorry, but i am really enthusiastic about explicit typing.  i will
> probably start to annotate expressions like "3" soon...  (-:
>
> could anybody tell me how i get this one straight?
>
> # let (a: int, b) = (1, 3) in a;;
> # let (a, b) : int * int = (1, 3) in a;;

# let (a : int), b = 1, 2;;
val a : int = 1
val b : int = 2

# let (a, b : int * int) = 1, 2;;
val a : int = 1
val b : int = 2

You can add more ( ) around tuples, but here you don't really define
tuples.

In theory, you could find all this information here:
  http://caml.inria.fr/ocaml/htmlman/manual008.html

Martin


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[Caml-list] Polymorphic Variant Error message (CVS version)

[skaller]

Consider:
--------------------------------------
# type t = [`A of t]
  let rec f (x:t) = match x with
  | `A y -> f y
  | `B y -> f y
;; 

Warning: this pattern-matching is not exhaustive.
Here is an example of a value that is not matched:
`AnyExtraTag
Warning: this match case is unused.
type t = [ `A of t ]
val f : t -> 'a = <fun>
------------------------------------------
The first error message is a bit confusing.
There is indeed an extra tag `B in the match.

I think this kind of message only occurs where there
is a covariant type.

The confusion is: it says the pattern matching
is not exhaustive, but from the developers viewpoint
the opposite is true: the match is overconstrained,
rather than underconstrained. I guess the problem arises
becase the type of x is deduced from the match first,
before the annotation restricts it to type t.

Anyhow just curious exactly how this error arises.

--
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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