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Date: Fri, 17 Apr 2009 09:26:28 +0900 (JST)
Message-Id: <20090417.092628.161183757.garrigue@math.nagoya-u.ac.jp>
To: dra-news@metastack.com
Cc: goswin-v-b@web.de, caml-list@inria.fr
Subject: Re: [Caml-list] pattern matching and records vs tuples
From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
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X-Spam: no; 0.00; ocaml:01 tohoku:01 val:01 val:01 compiler:01 sml:01 sml:01 caml-list:01 tuples:01 string:02 garrigue:03 garrigue:03 jacques:03 jacques:03 pattern:04 

From: "David Allsopp" <dra-news@metastack.com>

> The other worry in the back of my mind is that despite having
> considerably more flexible records in SML (you don't have to declare
> the types in advance and label sharing is possible), a function in
> SML still has the restriction of only being over a fixed record
> type... and when SML has odd restrictions, they're usually to do with
> the more "obvious" type system feature being undecideable. For
> example, you can't say in SML:
> 
> fun get_x r = #x r;
> 
> as the equivalent of the OCaml get_x you propose.

You can do this with SML#

http://www.pllab.riec.tohoku.ac.jp/smlsharp/

 # fun f x = #name x;
 val f = fn : ['a, 'b#{name:'a}. 'b -> 'a]
 # f {name = "Joe", age = 21};
 val it = "Joe" : string

But the compiler is rather clever...

Jacques Garrigue