A New Datatype: Typeset!

This article has been changed from its original posting. The word "typemap" has been changed to "typeset".

In REBOL 3.0, a typeset is essentially a set of datatypes.

For example, when you define a function, you specify the datatypes of arguments in this way:

f: func [arg1 [integer! number!] arg2 [string! url!]] ...

What follows each arg word is a set of accepted datatypes.

REBOL 3.0 adds a new datatype called a typeset! A typeset is simply a compact, high-performance method of storing the datatype sets as a new kind of datatype. Typesets are important because the interpreter uses them to quickly validate function arguments.

The typeset! datatype knows how to convert a block of datatype names such as [integer! decimal! money!] into an internal representation (similar to the bitset datatype). It can also convert the internal format back to a block for output or changes.

The addition of typesets eliminates the need for the special REBOL pseudo-datatypes like series! and number!. These are now implemented as typesets, but you can use them the same way as before. They can be used in function argument specifications:

f: func [arg1 [number!] arg2 [series!]] ...

and also for datatype tests:

if series? value [....]

Note, however, this difference. In REBOL 2.*:

type? series!
datatype!

in REBOL 3.0 becomes:

type? series!
typeset!

For advanced users, REBOL 3.0 will provide a way to create and manage your own custom typesets.

tmp-type: make typeset! [time! money! percent!]

f: func [arg1 [tmp-type]] [...]

I will post more soon about a few issues related to typesets.

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