want better error msg with Class Read

[Alastair Reid]

> Why not just define your own function, much like `read`, that
> produces a more suitable error message?

readsPrec (i.e., the class method) doesn't report how far it got when
it reports failure.

One could change that but this requires a change to the report and to
the code compilers derive when you type 'deriving Read' and the code
in the prelude and any libraries you use.  This is worthwhile but is
quite a large change.

--
Alastair Reid                 alastair@reid-consulting-uk.ltd.uk  
Reid Consulting (UK) Limited  http://www.reid-consulting-uk.ltd.uk/alastair/