[Caml-list] Associativity precedence for the user-defined operator.

[Caml-list] Associativity precedence for the user-defined operator.

[Claudio Trento]

Hi,

I've defined a set of new operetors, for instance:

let ( /+/ ) = add_num   (where add_num is a function that added two sometype 
			elements.) 

but I don't know if I can set associativity precedence for this operator,
writing: el1 ( /+/ ) el2 ( /+/ ) el3 without parenthesis, what happens?



Cheers,

Claudio 


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Re: [Caml-list] Associativity precedence for the user-defined operator.

[Richard Jones]

On Fri, Jul 23, 2004 at 04:27:06PM +0200, Claudio Trento wrote:
> 
> Hi,
> 
> I've defined a set of new operetors, for instance:
> 
> let ( /+/ ) = add_num   (where add_num is a function that added two sometype 
> 			elements.) 
> 
> but I don't know if I can set associativity precedence for this operator,
> writing: el1 ( /+/ ) el2 ( /+/ ) el3 without parenthesis, what happens?

The easiest way to control associativity and precedence seems to be to
write a Camlp4 extension.  For example here is a Camlp4 extension I
wrote to create some left-associative ('LEFTA') ops:

open Pcaml

EXTEND
   expr: AFTER "apply"
   [ LEFTA
       [ e1 = expr; "map_with"; e2 = expr ->
           <:expr< List.map $e2$ $e1$ >>
       | e1 = expr; "iter_with"; e2 = expr ->
           <:expr< List.iter $e2$ $e1$ >>
       | e1 = expr; "filter_with"; e2 = expr ->
           <:expr< List.filter $e2$ $e1$ >>
       | e1 = expr; "concat_with"; e2 = expr ->
           <:expr< List.concat (List.map $e2$ $e1$) >>
       | e1 = expr; "apply_with"; e2 = expr ->
           <:expr< $e2$ $e1$ >>
       ]
   ];
END

Rich.

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Re: [Caml-list] Associativity precedence for the user-defined operator.

[Jean-Baptiste Rouquier]

Claudio Trento wrote:

>Hi,
>
>I've defined a set of new operetors, for instance:
>
>let ( /+/ ) = add_num   (where add_num is a function that added two sometype 
>			elements.) 
>
>but I don't know if I can set associativity precedence for this operator,
>writing: el1 ( /+/ ) el2 ( /+/ ) el3 without parenthesis, what happens?
>
The manual says that here you have left associativity. See 
http://caml.inria.fr/ocaml/htmlman/manual015.html.

# let ( /+/ ) a b =
  Printf.printf "a=%i, b=%i\n%!" a b;
  a + b;;
    val ( /+/ ) : int -> int -> int = <fun>
# let _ = 1 /+/ 2 /+/ 39;;
a=1, b=2
a=3, b=39
- : int = 42


Cheers,
Jean-Baptiste.

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Re: [Caml-list] Associativity precedence for the user-defined operator.

[John Prevost]

In general, the associativity and precedence of an operator (unless
you go out to camlp4 or something) is based on the operator's first
character.  For example +/ would act like +, */ would act like *, and
so on.  For this reason, you'll often see O'Caml operators defined as
"basic operator followed by some strange symbol."  In your add_num
case, +/ and friends would probably mesh well.  Then you also get the
expected interaction when mixing +/ and */.

John.

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