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Re: Namespaces

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Albert van der Horst at wrote on 05/07/2013 16:28:

> 
> I've abondaned VOCABULARY and embraced NAMESPACE (since ciforth 5 beta,
> that is already 5 years ago.) :
>     Compile time: create a wid and remember it.
>     Execute: add the wid to the search order.
> This indeed implements what are called namespaces in main stream
> computer science.
> 
> Traditional implementations of VOCABULARY have replace the topmost
> word of the search order, such that each invocation of a VOCABULARY
> is preceeded by ALSO . Not only does this makes no sense, but it also
> serves to confuse an orderly use of namespaces.
> 
There is a problem with the ANS Standard in that the wordlist definitions
have side-effects on the search order.  The Technical Committee indeed
accepted that the implementation of ALSO and ONLY, with their hidden and not
very intuitive effects, was controversial.

My solution has been to put a 'pre-processor' in of font for my own code, if
I want to use a different Forth system.  The basic idea is to separate the
definitions of vocabularies with the words that directly affect the search
order.  

For a VOCULARY (not defined in the Standard),

VOCABULARY ( ³name² -- )
Define a new named wordlist that returns its wid on the stack.

Then
FORTH ( -- wid)
Return the Forth word list.  This is a synonym for FORTH-WORDLIST, which
becomes redundant.

ASSEMBLER ( -- wid)
Returns the assembler word list.  Not used in high-level Forth applications.

These are simple word list definitions.  Definitions that affect the search
order or compilation word list are:

DEFINITIONS ( wid -- )
Set the compilation wordlist to wid.  Add wid to the search order if not
already on the top.

ALSO ( wid -- )
Add the wid argument to the top of the search order.

There are four definitions addition to the above:

VIA (--)
Starts a VIA Š ENDVIA sequence.  Clears the search order.  Expects a list of
vocabulary names in the sequence to be placed on the search stack in the
same order as SET-ORDER and GET-ORDER, i.e. last named first to be searched.

ENDVIA (--)
Terminates a list of VIA names.

There are also a couple useful words used in assembler:

TRANSIENT ( wid -- )
Pushes a transient vocabulary/word-list on top of the search-order.  The
transient is discarded whenever a new definition is added to the dictionary
and only one can be used at a time.

NO-TRANSIENT ( -- )
Removes any transient from on top of the search order.

The is convenient in mixed CODE and colon environments.  If a CODE
definition includes ASSEMBLER TRANSIENT, adds assembler to the top of the
search-order to whatever else is needed for the search (assembler search
first) but removes the assembler when a new definition is added to the
dictionary (which may be a colon definition).  In mixed colon and assembler
code, the assembler search can be discarded in a colon segment with
NO-TRANSIENT.

ONLY is no longer needed and is a pretty obscure definition any way.

As an example, my Pascal parser uses 12 vocabularies - they are best held in
the Forth vocabulary.

In line in execute mode

SCAN-CONTROLS DEFINITIONS
    VIA  SCAN-CONTROLS FORTH  ENDVIA       \ Need FORTH for building defns.
        -- FORTH searched first so that ( : and ; are seen as FORTH versions

This searches Forth first as the SCAN-CONTROLS need to use Forth versions or
( : and ;
    On the other hand, when we actually want the list of token definitions
we search FORTH last.  Note that VIA...ENDVIA in this case is held inside a
colon definition.

    \ Starting macros and compound tokens in token definition-list
: TokenDefinitions
    SCAN-CONTROLS DEFINITIONS              \ Compile to SCAN-CONTROLS vocab
    VIA  FORTH CHARACTER-CLASSES SCAN-CONTROLS  ENDVIA ;
        \ Search scan controls, character classes & FORTH last

Usually, all the vocabularies are held in Forth it self, so any named
vocabulary can be included in a VIA...ENDVIA sequence.  Hidden vocabularies
can still be used if the relevant vocabularies are all made visible.

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Re: Namespaces Ian van Breda <igvb@btopenworld.com> - 2013-08-06 14:25 +0100

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