Non-H98 crusade, contd.

Jon Fairbairn Jon.Fairbairn at
Mon Feb 28 15:39:48 EST 2005

On 2005-02-28 at 20:22GMT Keith Wansbrough wrote:
> > > The reason
> > > was that error messages for beginners' code were rather baffling.
> > > (And pretty baffling for some experts too!)
> > 
> > I don't understand how they could be more baffling than any other type
> > errors involving monads.  Can you give an example?  (I could not find
> > any, only mentions of them.)  Maybe error messages were less clear then?
> > Or maybe understanding of monads was less pervasive?
> Beginners are taught lists and list comprehensions before they are
> taught monads.  The errors they saw involved monads, which they didn't
> yet know about.  Confusion reigned.

True, but it was still the wrong solution to the problem;
Something involving a "beginners prelude" -- which would fit
well with the idea of less in the standard prelude -- would
avoid the annoyance that mplus isn't (++) and so on.

I don't think it's too onerous to tell beginners that "you
have to put

  import Didactic {- or whatever -}

at the front of all Haskell programmes" ... followed several
lectures later by "OK, I lied".


Jón Fairbairn                              Jon.Fairbairn at

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