Re: Type checking (was: The strengths of FORTH)

"m_l_g3" <m_l_g3@[EMAIL PROTECTED]
> schrieb im Newsbeitrag 
news:b6409894-74ed-4089-a21a-3451cd458581@[EMAIL PROTECTED]
> On Apr 8, 3:22 pm, Jonah Thomas <jethom...@[EMAIL PROTECTED]
> wrote:
>> "Stephan Becher" <stephan.remove-this.bec...@[EMAIL PROTECTED]
> wrote:
>> > "Bernd Paysan" <bernd.pay...@[EMAIL PROTECTED]
> schrieb
....

>> > Furthermore, some words like ?DUP and FIND are simply incompatible
>> > with strong static type checking, because their stack effects are not
>> > known at compile time.
>
> In fact, ?DUP has the stack effect ( x -- x/xx ), and
> IF can be described as ( x/xx -- x ; no jump ) ( x/xx -- ; jump )
> so ?DUP IF would work...

Yes. In the utilities of StrongForth 1.3, three words are provided that 
implement the semantics of
?DUP IF, ?DUP WHILE and ?DUP UNTIL. They are called ?IF, ?WHILE and
?UNTIL, respectively.

> Another awful ANS Forth data type is ( xn ... x1 n ), but it also can
> be resolved.
> IIRC, pointers are parametrized with the data type they point to;
> the same thing may be dome for { x }*n.

That's indeed an awful data type. In order to be able to include
SAVE-INPUT, 
RESTORE-INPUT,
GET-ORDER and SET-ORDER (which all use this data type), I added a special 
data type called
TUPLE that covers a variable number of cells. It is usually used in a 
qualified form like TUPLE -> WID. Operations on TUPLE are NULL TUPLE
(create 
an empty tuple), >T (add a cell), T> (remove a cell), SIZE and DROP. This
is 
sufficent to implement the above mentioned words and it works very well.
The 
only yet unresolved issue is that CATCH cannot be applied to words whose 
stack diagrams contain a tuple, because the size of the tuple cannot be 
evaluated at compile time.

>> It looks like a lot of effort but so far I don't see any gotchas that
>> would keep it from working.
>
> I think, a bit less labor than for a Forth system from scratch,
> comparable to that for a Forth Assembler or a bit more. (Test suites
> and docs not counted).

Stephan