Programming in stack-based languages is notoriously error-prone: it is way
too easy to lose track of where an operand on the stack came from, and
leave too many or too few operands for an operation.

GXScript <https://bitbucket.org/ldo17/gxscript> defines operators “</” (which I call “stackbegin”) and “/>” (which I call “stackend”). They are
used as follows:

«n» </

where «n» is a non-negative integer, pops «n» operands off the top of the current operand stack (obviously it must contain at least that many), and
puts these on a new operand stack, which becomes the current stack, while
the previous stack becomes (temporarily) inaccessible, but saved on a
stack of stacks, as it were.

Correspondingly,

«n» />

verifies that the current operand stack contains exactly «n» items; it
pops these off, discards the current operand stack, restores the previous
one, and pushes those values on.

The stack of stacks allows these </ ... /> sequences to be nested to any desired depth.

The “;” operator is quite simple: it asserts that the current operand
stack is currently empty, raising an error if not.

Simple, even trivial, example:

/try
{
2 </
add
1 />
}
ddef

2 3 try = ;

prints

5

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On 12/29/2024 8:49 PM, Lawrence D'Oliveiro wrote:

Programming in stack-based languages is notoriously error-prone: it is way too easy to lose track of where an operand on the stack came from, and
leave too many or too few operands for an operation.

gforth allows the use of "locals" in cases like this: https://gforth.org/manual/Local-Variables-Tutorial.html

Of course many on comp.lang.forth believe if you are having trouble
keeping track of your stack operands, you should break up your function
(aka Forth word) into multiple smaller words. So some say that losing
track of stack operands is a Forth language feature that tells you that
you are not writing your Forth program correctly.

BTW, I really applaud the work you are doing. I would use PostScript
more than I already do if it had double precision floating point math capabilities. I've always toyed with the idea of including the math
needed to compute an engineering equation and a graph/figure to
illustrate it in a single unified program. I haven't pursed it on
PostScript because of the precision issue.

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On Fri, 3 Jan 2025 08:53:44 -0800, Buzz McCool wrote:

On 12/29/2024 8:49 PM, Lawrence D'Oliveiro wrote:

Programming in stack-based languages is notoriously error-prone: it is
way too easy to lose track of where an operand on the stack came from,
and leave too many or too few operands for an operation.

gforth allows the use of "locals" in cases like this: https://gforth.org/manual/Local-Variables-Tutorial.html

I have local variables, too. With lexical binding and full reentrancy. I
think I posted an example of that previously; shall I do it again?

I would use PostScript more than I already do if it had double precision floating point math capabilities.

Since my implementation is in Python, I use Python floats, which are
double precision.

I've always toyed with the idea of including the math
needed to compute an engineering equation and a graph/figure to
illustrate it in a single unified program.

I would recommend using Cairo graphics to do that -- it offers a more
modern graphics API than PostScript <https://www.cairographics.org/>.

There are several Python bindings for this. Here is mine <https://gitlab.com/ldo/qahirah>.

For convenient presentation of information in rich-output form, might I
suggest using Jupyter notebooks <https://jupyter.org/>.

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On 1/3/2025 1:23 PM, Lawrence D'Oliveiro wrote:

I have local variables, too. With lexical binding and full reentrancy. I think I posted an example of that previously; shall I do it again?

Sure.

I think you should archive your GXScript postings somewhere like on your bitbucket site. My news server doesn't keep articles very long.

I would use PostScript more than I already do if it had double precision
floating point math capabilities.

Since my implementation is in Python, I use Python floats, which are
double precision.

Great

I've always toyed with the idea of including the math
needed to compute an engineering equation and a graph/figure to
illustrate it in a single unified program.

I would recommend using Cairo graphics to do that -- it offers a more
modern graphics API than PostScript <https://www.cairographics.org/>.

There are several Python bindings for this. Here is mine <https://gitlab.com/ldo/qahirah>.

For convenient presentation of information in rich-output form, might I suggest using Jupyter notebooks <https://jupyter.org/>.

Thank you for the information. I still think I'm looking for something
more like PostScript with double precision math.

Also, GXScript could use a better name (especially if you don't have the GX/graphics part working yet). MostScript? BoastScript?

Good Luck with your endeavor!

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On Mon, 6 Jan 2025 08:03:44 -0800, Buzz McCool wrote:

On 1/3/2025 1:23 PM, Lawrence D'Oliveiro wrote:

I have local variables, too. With lexical binding and full reentrancy.
I think I posted an example of that previously; shall I do it again?

Sure.

Examples from Language.txt in the repo:

/Count 99 ddef

/metatry
{ # provides context for nonlocals
dup
/Name exch ldef
/Count 0 ldef
{ # actual proc
/Count dup lload 1 add lstore
/Count dup dload 1 add dstore
Name =
(local Count = ) print /Count lload =
(global Count = ) print /Count dload =
(whichever Count = ) print Count =
}
}
ddef

/try1 metatry ddef
/try2 metatry ddef

try1
try2
try1
try2

produces output

try1
local Count = 1
global Count = 100
whichever Count = 1
try2
local Count = 1
global Count = 101
whichever Count = 1
try1
local Count = 2
global Count = 102
whichever Count = 2
try2
local Count = 2
global Count = 103
whichever Count = 2

and

/try1
{
/Count 31 ldef
{ # actual body
/Count Count 1 add lstore
(try1 Count = ) print Count =
}
} exec
ddef

/try3
{
/try1 exch ldef
/Count 5 ldef
/try2
{
/Count Count 1 add lstore
(try2 Count = ) print Count =
}
ldef
try1
try2
try1
try2
}
ddef

/try1 dload try3

produces output

try1 Count = 32
try2 Count = 6
try1 Count = 33
try2 Count = 7

For convenient presentation of information in rich-output form, might I
suggest using Jupyter notebooks <https://jupyter.org/>.

Thank you for the information. I still think I'm looking for something
more like PostScript with double precision math.

PostScript won’t give you the interactivity and rich output that Jupyter does.

Also, GXScript could use a better name (especially if you don't have the GX/graphics part working yet).

That part is called “ToastScript” <https://bitbucket.org/ldo17/gxscript_extensions/>, and while it is not
yet what I would call complete, parts are working.

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