From: Jacques Carette <carette@mcmaster.ca>
To: David Allsopp <dra-news@metastack.com>
Cc: "'OCaml List'" <caml-list@yquem.inria.fr>
Subject: Re: [Caml-list] Re: Polymorphic variants question
Date: Fri, 01 Sep 2006 16:40:42 -0400 [thread overview]
Message-ID: <44F89ACA.2000202@mcmaster.ca> (raw)
In-Reply-To: <015101c6ce00$d47c36f0$6a7ba8c0@treble>
David Allsopp wrote:
> Incidentally, if I use an annotation free version
>
> let f x = if x = `A then (true, `B) else (false, (x : [< `A | `C] :> [> `A |
> `C]))
>
> then the inferred type of x is [< `A | `C > `A ] ... what does that mean?
>
This is a "point free" notation for what mathematicians would have written
`A <= x <= `A | `C
In other words, x is strictly bounded above and below by those 2 types.
Translated into english, this means that the type from which x comes
*must* contain an `A and *may* contain a `C and *must not* contain
anything else.
For example, trying
let g x = f (snd (f x))
would not type.
Jacques
next prev parent reply other threads:[~2006-09-01 20:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-01 17:31 David Allsopp
2006-09-01 18:33 ` Chris King
2006-09-01 19:00 ` [Caml-list] " skaller
2006-09-01 19:57 ` David Allsopp
2006-09-01 20:40 ` Jacques Carette [this message]
2006-09-01 18:40 ` [Caml-list] " Olivier Andrieu
2006-09-01 19:26 ` Jon Harrop
2006-09-01 19:29 ` skaller
2006-09-01 20:49 ` Andres Varon
2006-09-02 11:16 ` Jacques Garrigue
2006-09-03 1:22 ` Andres Varon
2006-09-03 9:08 ` Jacques Garrigue
2006-09-03 15:00 ` Andres Varon
2006-09-03 23:18 ` Jacques Garrigue
2006-09-03 0:48 ` [Caml-list] Polymorphic variants problem skaller
2006-09-03 1:12 ` Andres Varon
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