Re: [Caml-list] ocaml and named constants

[John Max Skaller <skaller@ozemail.com.au>]

Andreas Rossberg wrote:

> >         Is there any semantic reason why
> > one cannot use variables, or even expressions? Apart from
> > the obvious syntactic problem.
> 
> If you allow arbitrary (dynamically determined) values to be matched
> against, then pattern matching has unbound cost.

> OTOH, with the current
> form, the cost of pattern matching is always linear in the syntactic
> size of the match. 

	Unless you use a 'when' construct .. which already
provides what I was asking for. The case when this is most
annoying is for 'manifest constants':

	let c1 = 1
	and c2 = 2
	in match expr with
	| x when x = c1 -> ..
	| x when x = c2 -> ..

where the 'match' construction is still arguably cleaner than
an if/then/else chain

	let x = expr in
	if x = c1 then ..
	else if x = c2 then ..

especially if you're actually matching as well:

	match expr with
	| (x,y) when x = c1 -> ...

-- 
John (Max) Skaller, mailto:skaller@maxtal.com.au
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
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