design problem
 Pietro Abate
[
Home
]
[ Index:
by date

by threads
]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
[ Message by date: previous  next ] [ Message in thread: previous  next ] [ Thread: previous  next ]
Date:  20061101 (05:39) 
From:  Pietro Abate <Pietro.Abate@a...> 
Subject:  design problem 
Hi all, I've the following code to write types and functions in an extensible way, so to reuse my code a bit. Everything seems working fine. I've two questions:  Is there a better way of achieving a similar result ? Here I'm using polymorphic variants, but I'm wondering if somebody already cooked something together by using variants and camlp4 extensions...  At the moment type errors are pretty horrible. How can I coerce these functions to give prettier errors ? I've tried to coerce the function f in the *_aux functions below, but of course this is not possible as it needs to be polymorphic by design ... thanks :) p (* my basic data type *) type 'a termpc = [`And of 'a * 'a `Or of 'a * 'a `Not of 'a `Atom of string ] ;; (* a simple normal form function *) let nnfpc_aux f = function `Not ( `Not x ) > f x `Not ( `And(x,y) ) > `Or (f (`Not x), f (`Not y) ) `Not ( `Or (x,y) ) > `And (f (`Not x), f (`Not y) ) `And (x,y) > `And (f x, f y) `Or (x,y) > `Or (f x, f y) `Not ( `Atom _) as x > x `Atom _ as x > x _ > failwith "impossible pc" ;; let rec nnfpc t = nnfpc_aux nnfpc t;; (* extension of the basic data type *) type 'a termk = [`Dia of 'a `Box of 'a 'a termpc ] ;; let nnfk_aux f = function `Not (`Dia x ) > `Box (f (`Not x)) `Not (`Box x ) > `Dia (f (`Not x)) `Dia x > `Dia (f x) `Box x > `Box (f x) #termpc as x > nnfpc_aux f x _ > failwith "impossible k" ;; let rec nnfk t = nnfk_aux nnfk t;; (* an other extension on top of termk *) type 'a termlck = [`CDia of 'a `CBox of 'a 'a termk ] ;; let rec nnflck_aux f = function `Not (`CDia x ) > `CBox (f (`Not x)) `Not (`CBox x ) > `CDia (f (`Not x)) `CDia x > `CDia (f x) `CBox x > `CBox (f x) #termk as x > nnfk_aux f x _ > failwith "impossible lck" ;; let rec nnflck t = nnflck_aux nnflck t;; let a = `Not (`Not (`Not (`Dia (`CDia (`Atom "a")))));; let b = nnflck a;;  ++ Blog: http://blog.rsise.anu.edu.au/?q=pietro ++ ++ "All great truths begin as blasphemies." George Bernard Shaw ++ Please avoid sending me Word or PowerPoint attachments. See http://www.fsf.org/philosophy/nowordattachments.html