stupid q(2): camlp4

stupid q(2): camlp4

[Anastasia Gornostaeva]

Hello.

Readihg http://martin.jambon.free.fr/extend-ocaml-syntax.html, I
attempt to solve the exercise from chapter 13: 

"Suggested exercise: implement and test a syntax extension which supports a
 where construct. For instance,

 a + b where a = 1 and b = 2

 means

 let a = 1 and b = 2 in a + b

 We decide that

 let a = 1 in a where a = 2

 should be read as

 let a = 1 in (a where a = 2) (* returns 2 *)

 and not

 (let a = 1 in a) where a = 2 (* returns 1 *)

 Also, the where construct is right-associative:

 x + y where x = y where y = 1

 means

 x + y where x = (y where y = 1) (* depends on an external y *)

 and not

 (x + y where x = y) where y = 1 (* returns 2 *)"

I wrote (for old camlp4/camlp5):

EXTEND
expr: LEVEL "expr1"
  [ RIGHTA
    [ x = SELF; "where"; lb = V (LIST1 let_binding SEP "and") ->
      <:expr< let $_list:lb$ in $x$ >> ]
  ];
END

but it does not satisfy the second suggestion. How can I have true RIGHTA
associative?

Thanks!

ermine

Re: [Caml-list] stupid q(2): camlp4

[Richard Jones]

On Wed, Nov 12, 2008 at 04:13:00PM +0300, Anastasia Gornostaeva wrote:
> Hello.
> 
> Readihg http://martin.jambon.free.fr/extend-ocaml-syntax.html, I
> attempt to solve the exercise from chapter 13: 
> 
> "Suggested exercise: implement and test a syntax extension which supports a
>  where construct. For instance,
> 
>  a + b where a = 1 and b = 2
> 
>  means
> 
>  let a = 1 and b = 2 in a + b

You could cheat and have a look at pa_where ...

http://bluestorm.info/camlp4/pa_where/list.php
http://bluestorm.info/camlp4/pa_where/pa_where.ml.html

(Is bluestorm running a gopher server?)

Rich.

-- 
Richard Jones
Red Hat

Re: [Caml-list] stupid q(2): camlp4

[Anastasia Gornostaeva]

On Wed, Nov 12, 2008 at 10:49:34PM +0000, Richard Jones wrote:

[...]
> 
> You could cheat and have a look at pa_where ...
> 
> http://bluestorm.info/camlp4/pa_where/list.php
> http://bluestorm.info/camlp4/pa_where/pa_where.ml.html

It does not explain why RIGHTA in my code does not work as expected...
and the implementation for let_binding in that pa_where is too complex for
too simple task.

ermine

Re: [Caml-list] stupid q(2): camlp4

[Anastasia Gornostaeva]

On Wed, Nov 12, 2008 at 10:49:34PM +0000, Richard Jones wrote:

[...]

> You could cheat and have a look at pa_where ...
> 
> http://bluestorm.info/camlp4/pa_where/list.php
> http://bluestorm.info/camlp4/pa_where/pa_where.ml.html

Ouch, I got it after reading 
http://brion.inria.fr/gallium/index.php/Syntax_extension_tutorial
- it depends not only associative but even on level of adding the rule!
Big thanks for excellent tutorials. :)

ermine