Syntax for union types

P T Withington ptw at pobox.com
Sat Nov 10 13:02:33 PST 2007


+1 for |

On 2007-11-09, at 13:21 EST, Brendan Eich wrote:

> As Lars suggested, we have bigger fish to fry, but we settled on
> union syntax quickly and were content to stay there. I'm not against
> | instead of , and if enough people think it's the right user
> interface, we could consider it again. I'm not saying it's a good use
> of time to fuss over this, but it's "fixable" if (T, U, ...) is not
> as good as (T | U | ...).
>
> Recall that ES4 and indeed JavaScript do not have tuples, so we want
> to use [T, U] for the array structural type describing a tuple of at
> least index 0 of type T and index 1 of type U. If we ever did add
> tuples, then Yuh-Ruey has a point I think: we might rather use (T |
> U) for union of T and U, and (T, U) -- or possibly (T, U,) to match
> expression syntax (which would have to be (e1, e2,) to avoid
> ambiguity with comma expression) for tuple type.
>
> /be



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