General pattern bindings

[Stefan O'Rear]

On Sat, Apr 14, 2007 at 03:43:03AM +0200, Twan van Laarhoven wrote:
> In the interest of removing things from the standard, I found this in 
> the Haskell 98 report (section 4.4.3.2):
> 
> > The general form of a pattern binding is p match, where a match is the
> > same structure as for function bindings above; in other words, a
> > pattern binding is:
> >
> > p 	| g1 	= e1
> >	| g2 	= e2
> >	...
> >	| gm 	= em
> >	where { decls }
> 
> I did not even know these things existed, is there anyone who actually 
> uses general pattern bindings?
> 
> If not, the question becomes whether removing these bindings would 
> improve the language. It can be argued that it makes the language less 
> consistent. Declarations would change from
> 
> > decl   ->    (funlhs | pat0) rhs
> > rhs    ->    = exp [where decls]
> >        |     gdrhs [where decls]
> 
> to something like
> 
> > decl   ->    funlhs rhs
> >        |     pat0 srhs
> > srhs   ->    = exp [where decls]
> > rhs    ->    srhs
> >        |     gdrhs [where decls]
> 
> On the other hand, we can remove most of section 4.3.2.2.
> 
> Any opinions?

At one point vty defined the standard colors using the following wonderfully elegant code:

[black, red, green, yellow, blue, magenta, cyan, white] = map Color [0..7]

Unfortunately ghc generated hideous code for this, so I had to inline
it manually.  So it goes.  (yow, what got into me there?)

I'm pretty sure I've seen this once or twice:

(x,y) | someCondition = x y z
      | otherwise     = b a r

Stefan