= vs ->
Fri, 12 Oct 2001 17:56:32 +1000
On 10-Oct-2001, D. Tweed <email@example.com> wrote:
> On Wed, 10 Oct 2001, Mark Carroll wrote:
> > On 10 Oct 2001, Ketil Malde wrote:
> > (snip)
> > > function definitions. Perhaps one could have had a syntax like
> > >
> > > z a =
> > > | a == 1 -> 1
> > > | a == 2 -> 3
> > >
> > > instead, as it'd make it more consisten with the case, but I suppose
> > > there's a reason for it being the way it is. The case statement is an
> > (snip)
> > Ah, yes - it was this 'discrepancy' that was one of the sources of my
> > confusion, as "a == 1" obviously doesn't 'equal' "1".
> I think this comes about from history; in the functional languages like
> Miranda & Orwell that preceded Haskell an extended version of the function
> above would have been written
> z a = 1 if a==1
> = 2 if a==2
> = 3 otherwise
> which looks a lot like traditional mathematics and where the equals makes
> sense. I'm not sure why anymore but Haskell changed the `if clause after
> the value' to `pattern guard | before =', so I agree it now looks as if
> it's stating that the pattern guard is equal to the rhs.
I've heard that the company which trademarked "Miranda" also obtained
a design patent on using syntax like that in a programming language.
The enforcibility of such a design patent is IMHO legally dubious,
and the application of design patents to programming languages has
never been tested in court as far as I am aware. But nevertheless
the mere existence of such a design patent was probably a significant
disincentive to using that syntax.
Fergus Henderson <firstname.lastname@example.org> | "... it seems to me that 15 years of
The University of Melbourne | email is plenty for one lifetime."
WWW: <http://www.cs.mu.oz.au/~fjh> | -- Prof. Donald E. Knuth