[Caml-list] Pattern matching missing (or brain damage?)

[Caml-list] Pattern matching missing (or brain damage?)

[Alessandro Baretta]

I believe I remember a pattern matching construct where an 
expression could be associated with multiple patterns.

match <expr> with
| A(_) | B(_) | C(_) -> foo
| C(_) | D(_) | E(_) -> bar

Neither does the compiler accept such code, nor does the 
manual mention such construct. Has it been removed from the 
language or am I suffering severe brain damage from too much 
O'Caml coding?

Alex

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Re: [Caml-list] Pattern matching missing (or brain damage?)

[Michael Vanier]

# type ex = A of int | B of int | C of int | D of int | E of int;;
type ex = A of int | B of int | C of int | D of int | E of int
# let a = A 1000;;
val a : ex = A 1000
# match a with
     A(_) | B(_) | C(_) -> "foo"
  |  C(_) | D(_) | E(_) -> "bar";;
- : string = "foo"

You put in an extra | before the A(_).

Mike


> Date: Fri, 19 Jul 2002 00:22:44 +0200
> From: Alessandro Baretta <alex@baretta.com>
> 
> I believe I remember a pattern matching construct where an 
> expression could be associated with multiple patterns.
> 
> match <expr> with
> | A(_) | B(_) | C(_) -> foo
> | C(_) | D(_) | E(_) -> bar
> 
> Neither does the compiler accept such code, nor does the 
> manual mention such construct. Has it been removed from the 
> language or am I suffering severe brain damage from too much 
> O'Caml coding?
> 
> Alex
> 
> -------------------
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Re: [Caml-list] Pattern matching missing (or brain damage?)

[William Lovas]

On Fri, Jul 19, 2002 at 12:22:44AM +0200, Alessandro Baretta wrote:
> I believe I remember a pattern matching construct where an 
> expression could be associated with multiple patterns.
> 
> match <expr> with
> | A(_) | B(_) | C(_) -> foo
> | C(_) | D(_) | E(_) -> bar
> 
> Neither does the compiler accept such code, nor does the 
> manual mention such construct. Has it been removed from the 
> language or am I suffering severe brain damage from too much 
> O'Caml coding?

This is legal.  It's covered in the Chapter 6 of the manual, under
Patterns, sub-heading ``Or'' patterns:

    http://caml.inria.fr/ocaml/htmlman/manual014.html

You might be having trouble if your subpatterns don't bind exactly 
the same variables...

William
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Re: [Caml-list] Pattern matching missing (or brain damage?)

[Alessandro Baretta]

William Lovas wrote:
> 
> This is legal.  It's covered in the Chapter 6 of the manual, under
> Patterns, sub-heading ``Or'' patterns:
> 
>     http://caml.inria.fr/ocaml/htmlman/manual014.html
> 
> You might be having trouble if your subpatterns don't bind exactly 
> the same variables...

Many thanks to both William and Michael.

No, I was not having trouble with the bindings, since I was 
only checking the variant tag. The problem is that I'm still 
writing code at 3 in the morning. But at last I got it to 
compile, yeah! Tomorrow, debugging...

Alex

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Re: [Caml-list] Pattern matching missing (or brain damage?)

[Oleg]

On Thursday 18 July 2002 06:36 pm, Michael Vanier wrote:
> # match a with
>      A(_) | B(_) | C(_) -> "foo"
>   |  C(_) | D(_) | E(_) -> "bar";;
> - : string = "foo"
>
> You put in an extra | before the A(_).

It's optional

Regards,
Oleg
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