[ruby-talk:16438] Re: Symbolic Computation III

On Tue, 12 Jun 2001, Mathieu Bouchard wrote:

> > > 	ChoiceType.new foo,bar,baz
> > Reasonable, but I already know it's a Type.
> 
> It's not just a type. It's a class of types. ChoiceType.new foo,bar,baz
> creates a new type containing the three objects foo,bar,baz; you can test
> for membership.

ChoiceTypes?

> Maybe it's best to use "new" when there is a guarantee of returning a new
> object at every call (like Tuple);
> 
> and to use "of" when all returned objects are cached permanently (List
> and Union).

Isn't the caching an implementation detail?

A singleton pattern uses "new", even when subsequent calls will return
the cached object created with the first call.

> Btw I forgot to mention that in RX11 I use "Either" instead of "Union".
> Do you prefer the name "Either" ?

I think I know what you're aiming for. Union is a list of possible parse
paths, and only one of them will be taken?

Perhaps "Grammer", "Rules" or "Context"?

Seeing the example you posted:

> QRegexp = tuple([:pattern,QString|IString],[:flags,String])

makes it clearer how you intend this to be used. My suggestions would
make the above into:

  QRegexp = Tuple[:pattern, Union[QString, IString], [:flags, Union[String]]

Which doesn't look as good.

Perhaps the correct answer is "yes", and all of your proposals are good
ones...

Have the Thing[], Thing.new, Thing.of and Thing() forms... then if I care
about the caching, I can use "of", or if I'm me, I can use "new", or if
I'm Fred, I can use [].

Or if I'm Dave, I can use Thing[].new([*a ||= of]) or some other weird,
yet orthogonal, feature of the language. :)

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