Re: Libraries Digest, Vol 93, Issue 21

23 May 2011

      ...
Message: 3
Date: Sun, 22 May 2011 06:52:49 -0400
From: "Edward Z. Yang" 
Subject: Re: Proposal: Value strict versions of containers
To: Milan Straka 
Cc: libraries 
Message-ID: <1306061483-sup-1713@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