From Newsgroup: comp.lang.forth

On 03-07-2025 18:47, Ruvim wrote:

On 2025-07-03 17:11, albert@spenarnc.xs4all.nl wrote:

In article <1043831$3ggg9$1@dont-email.me>,
Ruvim-a <ruvim.pinka@gmail.com> wrote:

On 2025-07-02 15:37, albert@spenarnc.xs4all.nl wrote:

In article <1042s2o$3d58h$1@dont-email.me>,
Ruvim-a <ruvim.pinka@gmail.com> wrote:

On 2025-06-24 01:03, minforth wrote:
[...]

For me, the small syntax extension is a convenience when working
with longer definitions. A bit contrived (:= synonym for TO):

: SOME-APP { a f: b c | temp == n: flag z: freq }
\ inputs: integer a, floats b c
\ uninitialized: float temp
\ outputs: integer flag, complex freq
-a-a -a<: FUNC < ... calc function ... > ;>

BTW, why do you prefer the special syntax `<: ... ;>`
over an extension to the existing words `:` and `;`

-a-a-a : SOME-APP
-a-a-a-a-a-a [ : FUNC < ... calc function ... > ; ]
-a-a-a-a-a-a < ... >
-a-a-a ;

In this approach the word `:` knows that it's a nested definition and >>>>> behaves accordingly.

Or it has not even know it, if [ is smart enough to compile a jump to
after ].

This can be tricky because the following should work:

-a-a create foo [ 123 , ] [ 456 ,

-a-a : bar-a [ ' foo compile, 123 lit, ] ;

If this bothers you, rename it in [[ ]].

Once we enhance [ ] to do things prohibited by the standard,
(adding nested definitions) I can't be bothered with this too much.

The standard does not prohibit a system from supporting nested
definitions in whichever way that does not violate the standard behavior.

Yes, something like "private[ ... ]private" is a possible approach, and
its implementation seems simpler than adding the smarts to `:` and `;`
(and other defining words, if any).

The advantage of this approach over "<: ... ;>" is that you can define
not only colon-definitions, but also constants, variables, immediate
words, one-time macros, etc.

-a : foo ( F: r.coefficient -- r.result )
-a-a-a private[
-a-a-a-a-a variable cnt
-a-a-a-a-a 0e fvalue k
-a-a-a-a-a : [x] ... ; immediate
-a-a-a ]private
-a-a-a to k-a-a 0 cnt !
-a-a-a ...
-a ;

It's also possible to associated the word list of private words with the containing word xt for debugging purposes.

4tH has always allowed it, since it considered : and ; as branches -
like AHEAD. Since [: and ;] are just :NONAME and ; aliases they work essentially the same.

I never used it, because it would cause portability issues - and I
considered it "bad style".

The same goes for allocation (VARIABLE, VALUE, STRING, ARRAY). These are
in 4tH basically just directives - NOTHING IS ACTUALLY ALLOCATED. That
works just fine.

So the whole shebang would practically work out of the box. But of
course, to follow the complete example, I had to do the FP stuff as well
- and I wanted to do a bit of protecting the words between the tags.

In short, that boils down to this (for FOO):

1018| branch 1036 foo
1019| literal 1020
1020| branch 1030 <== jump after opcode 1030
1021| literal 0 <== mantissa 0
1022| literal 0 <== exponent 0
1023| variable 2 *k_f
1024| call 0 2!
1025| branch 1027 k <== DOES> definition
1026| variable 2 *k_f
1027| branch 7 2@ <== end DOES> def.
1028| branch 1029 [x]
1029| exit 0
1030| exit 0 <== end of "private"
1031| drop 0 <== drop the XT
1032| variable 2 *k_f
1033| call 0 2!
1034| literal 0
1035| to 1 cnt
1036| exit 0

Which is the compilant of this (preprocessor) code:

:macro ... ;
:macro private[ [: ;
:macro ]private ;] drop ;
:macro 0e 0 S>F ;

include lib/fp1.4th
include 4pp/lib/fvalue.4pp

: foo ( F: r.coefficient -- r.result )
private[
variable cnt
0e fvalue k
: [x] ... ; immediate
]private
fto k 0 cnt !
...
;

100 s>f foo k f. cnt ? cr

The weird code generated from 1021 - 1027 is the result of this code (generated by the preprocessor):

0 S>F FLOAT ARRAY k
AKA k *k_f LATEST F! :REDO k F@ ;

1. FP "zero" is thrown on the stack;
2. A variable with the capacity of a "float" is created (FVARIABLE);
3. Copy that symbol in the symbol table;
4. Initialize the FP variable;
5. Create a "DOES>" definition that fetches that value.

But it *does* work as advertised..

Hans Bezemer
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