Propsal: NoDatatypeContexts

Neil Brown nccb2 at
Mon Jul 19 05:17:41 EDT 2010

On 18/07/10 22:59, Ian Lynagh wrote:
> Hi all,
> H98 and H2010 allow a context to be given for datatypes, e.g. the
> "Eq a" in
>      data Eq a =>  Foo a = Constr a
> I have made a proposal to remove support for that context (ticket #139).
> More details are on the proposal wiki page:
To provide a data point: I was surprised to see CHP on the list of 
packages that didn't compile without data-type contexts, as I didn't 
realise I was using them.  I found one in a source file I haven't 
touched for a while, and removing it made no difference -- the library 
compiled fine.

I'm all for the proposal -- it stops people (like me!) inadvisedly using 
datatype contexts despite them not actually doing anything.



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