Libraries Digest, Vol 93, Issue 21

[John Lato]

>
>
> Message: 3
> Date: Sun, 22 May 2011 06:52:49 -0400
> From: "Edward Z. Yang" <ezyang at MIT.EDU>
> Subject: Re: Proposal: Value strict versions of containers
> To: Milan Straka <fox at ucw.cz>
> Cc: libraries <libraries at haskell.org>
> Message-ID: <1306061483-sup-1713 at ezyang>
> Content-Type: text/plain; charset=UTF-8
>
> Excerpts from Milan Straka's message of Sun May 22 06:50:07 -0400 2011:
> > - the types Data.IntMap.IntMap, Data.IntMap.Lazy.IntMap and
> >   Data.IntMap.Strict.IntMap should be equal -- so I can use strict
> >   methods on IntMap someone else created with lazy methods. That is
> >   simple in absence of type classes.
>
> Comment: This would mean you would get no static assurances against
> mixing up a strict IntMap with a lazy IntMap; for all intents and purposes,
> this is equivalent to implementing strict versions of all functions on top
> of a lazy data type.
>

Another consequence to this design is that, should someone want to have

> class MapC m key value | m -> key, m -> value where

it becomes impossible to directly write

> instance MapC (Data.IntMap.Strict.IntMap Int a) Int a where
>
> instance MapC (Data.IntMap.Lazy.IntMap Int a) Int a where

because the two instances are the same.

Regardless, +1 for Milan's proposal either with one type or separate types
for strict and lazy.

John Lato
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