Haskell report (August release)

Mark Tullsen [email protected]
Thu, 27 Sep 2001 12:34:59 -0700


Simon,

Here's a minor quibble with the organization of the Report and Library,
not with the content.  Sorry if this has been brought up before.

In section 4.3.3, Derived Instances, of the Report there is

  The only classes in the Prelude for which derived instances are
  allowed are Eq, Ord, Enum, Bounded, Show, and Read, all mentioned in
  Figure 5, ...  Classes defined by the standard libraries may also be
  derivable.

In the introduction to the Library Report there is

  Classes defined in libraries may be derivable. This report includes
  the derivation of such classes when appropriate.

Now, unless I missed something, the only class in the Library Report
which is derivable is Ix.

I would argue for bringing the Ix class into the Report for these reasons
 
  * One does not have to search through the Library Report to determine
    what is derivable.

  * I think one would expect that the Libraries contain stuff that could be
    implemented in Haskell by the user.  Until Haskell has the ability 
    to allow for user-defined derivable classes, Ix cannot be
    defined by the user.

- Mark