Re: [Caml-list] infix precedence

[dengping zhu <zhudp@cs.bu.edu>]

Hi, Daniel, I have to raise some questions about infix declaration in
camlp4 again.

Now I defined some infix as follows:
------------------------------------
let add_infix lev op = 
  EXTEND
      GLOBAL: Pcaml.expr;
          Pcaml.expr: LEVEL $lev$    
	      [ [ x = SELF; $op$; y = SELF -> <:expr< $lid:op$ $x$ $y$
	      >> ] ];   
	        END;; 

let _ = add_infix "*" ">>*"
let _ = add_infix "<" "wth"
let _ = add_infix "||" "|||"
------------------------------------

Then I have a following function:

  let f = number ||| literal '-' >>* number wth (fun x -> -x)

(where number and literal are some function I defined before.)

According to the infix definition above, this function should 
work as:

  let f = number ||| (literal '-' >>* number wth (fun x -> -x))

because the precedence of 'wth' is higher than that of '|||'.
But, it turns out to evaluate as:

  let f = (number ||| literal '-' >>* number) wth (fun x -> -x)

So, I have to add parenthesis so that it can work properly.
Can you help me to figure out this problem because I want to get rid of
the parenthesis so that my code is more readable? 

Thanks a lot!
Dengping


On Tue, 28 May 2002, dengping zhu wrote:

>Hi, Daniel, it works very well.
>Thanks a lot!
>
>Dengping
>
>
>
>
>On Wed, 29 May 2002, Daniel de Rauglaudre wrote:
>
>>Hi,
>>
>>On Tue, May 28, 2002 at 02:48:42PM -0400, dengping zhu wrote:
>>> 
>>> I tried camlp4 before. I got the example from the camlp4 tutorial and
>>> modified a little bit. 
>>
>>Your code cannot work: you are defining a new entry, you are not using
>>the entry of OCaml expressions, which is Pcaml.expr.
>>
>>  $ cat foo.ml
>>  let add_infix lev op =
>>  EXTEND
>>    GLOBAL: Pcaml.expr;
>>    Pcaml.expr: LEVEL $lev$
>>      [ [ x = SELF; $op$; y = SELF -> <:expr< $lid:op$ $x$ $y$ >> ] ];
>>  END;;
>>  $ ocaml
>>	  Objective Caml version 3.04+11 (2002-05-16)
>>  
>>  # #load "camlp4o.cma";;
>>	  Camlp4s Parsing version 3.04+11
>>  
>>  # #load "pa_extend.cmo";;    
>>  # #load "q_MLast.cmo";;  
>>  # #use "foo.ml";;
>>  val add_infix : string -> string -> unit = <fun>
>>
>>Type:
>>   Grammar.Entry.print Pcaml.expr;;
>>to see the current entry of expressions.
>>
>>The available levels are "top", "expr1", ":=", "||", "&&", "<", "^",
>>"+", "*", "**", "unary minus", "apply", "label", ".", "~-", "simple".
>>They are the one you can use as first parameter of add_infix:
>>
>>  # add_infix "*" "op1";;
>>
>>If you type
>>   Grammar.Entry.print Pcaml.expr;;
>>then you see that the rule with "op1" has been added in the level "*".
>>
>>  # let op1 x y = x + y + 1;;
>>  Toplevel input:
>>  # let op1 x y = x + y + 1;;
>>	^^^
>>  Parse error: 'module' uppercase identifier expected after 'let' (in
>>    [str_item])
>>
>>Normal, since "op1" is now a keyword. Mmmm... the normal form should be:
>>   let (op1) x y = x + y + 1;;
>>But it does not work... this is a bug in Camlp4 that I am going to fix.
>>
>>A solution should be to define it before the "add_infix"...
>>
>>But, in the meantime, this works:
>>   # let \op1 x y = x + y + 1;;
>>   val op1 : int -> int -> int = <fun>
>>   # 3 op1 4;;
>>   - : int = 8
>>
>>-- 
>>Daniel de RAUGLAUDRE
>>daniel.de_rauglaudre@inria.fr
>>http://cristal.inria.fr/~ddr/
>>-------------------
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>
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