Add back table<R>

[jclark]

Table is supposed to be iterable in its rows. This means the lang.table module needs an iterator function.

We previously allowed table<R> as a shorthand. With this we can write iterator like this:

@typeParam
private type Type = anydata|error;

public function iterator(table<Type> tbl) returns abstract object {
    public next() returns record {|
        Type value;
    |}?;
} = external;

Without this we would need to invent something else.

I am 90% sure we will want this anyway and it is still in the implementation. We can leave the semantics a bit vague until we fix issue #47.

[sanjiva]

So table<R> == table { *R; } right? So its a lightweight table without keys.

+1 for this.

[jclark]

Right, at least when R is closed.

[jclark]

We previous removed this for two reasons:

• mutation: mutating the values you get from an iterator does not affect the table, as it would do for map and T[]
• the record type has to be sealed, but it would be annoying to always require users to write the !...

But both of these can be dealt with:

• I believe tables should contain only frozen values, which means the record returned from an iterator can also be frozen
• open table types actually make sense and are useful, provided they are not used as inherent type