Getting in to metaprogramming

Eric_Dexter at msn.com Eric_Dexter at msn.com
Mon Dec 15 18:08:30 CET 2008


On Nov 27, 9:56 pm, "Hendrik van Rooyen" <m... at microcorp.co.za> wrote:
>  "Steven D'Aprano" <ste... at REM.com.au>
>
> >GUI designer. You write a program to let the user create code by clicking
> >buttons, dragging objects, drawing lines, etc. The GUI designer may use
> >classes, but the purpose of those classes is to generate source code.
>
> Yikes, this is getting hairy- If "the problem" is to generate source code,
> then you have to generate source code...
>
> >Testing code speed... you might have some functions with a loop, and you
> >want to unroll the loop as an optimization. If you have one function, you
> >can unroll it yourself. If you have a hundred such functions, you might
> >want to write a program to do it. (Yes, I'm stretching...)
>
> Ok this one I'll buy - I can't think of a way to do this dynamically in a
> class and get runnable code back. (but maybe I'm just not trying hard enough.)
>
>
>
> >Don't like that Python doesn't optimize tail-recursion? Then write a
> >source-code analyzer that detects tail-recursion and re-writes the
> >function using a while loop.
>
> This is like TJR's example (I think)
>
>
>
>
>
> >>> Thinking further back, when I was young and programming in Apple's
> >>> Hypercard 4GL, I used to frequently use Hypercard scripts to generate
> >>> new Hypercard scripts. That was to work around the limitations of the
> >>> scripting language.
>
> >> What sort of stuff did you do, and would having had simple OO available
> >> have rendered it unnecessary?
>
> >It's been 20-odd years, and the examples were pretty trivial... I don't
> >really recall exactly, but it would have been something like this:
>
> >* design a GUI involving lots of buttons on screen, each one with quite
> >similar but not identical code;
>
> >* since Hypercard didn't have a layout manager, write a script to
> >generate each button, place it where needed, and set the button's code.
>
> >Hypercard did have a message passing hierarchy (like inheritance for
> >objects), so often you could take the button's code and place it in a
> >higher level of the hierarchy (the card, the background, the stack), but
> >there were odd cases where that wasn't enough.
>
> >Another example: Hypercard had a very limited number of GUI elements
> >(text fields and buttons, basically) but I designed a slider control
> >using a few buttons, each button with a custom script. To avoid needing
> >to create and place the buttons by hand each time I wanted a slider, I
> >had a script that did it for me. The script not only created the buttons,
> >but it created the scripts used by the buttons. This wasn't as difficult
> >as it sounds -- it was basically taking a template and doing some text
> >replacements, then telling the button to use it as a script.
>
> Ok I think I am beginning to get the picture - when you have to do stuff
> that the language does not directly support, then you use the simple
> available elements, and create source code that strings them together
> to make more complex stuff. -in this case its probably not trivial to
> do it at run time.
>
> The "make the source code" then run it, introduces a kind of compiler
> stage.
>
> For an old assembler programmer, this is starting to sound like macros.
>
> So a different meta law would read like:
>
> One uses Code Generation Techniques when the language does not
> have macros.
>
> *ducks*
>
> - Hendrik- Hide quoted text -
>
> - Show quoted text -

I have been converting stuff like
sound 100, 1

exc...  and just writing like
100, 1

for a number of languages and then just loading it into a spreadsheet
so that I can save little pieces of songs exc..  I can even use
different compilers or libraries that way..  I have started doing that
for quickbasic, qbasic, free basic, qb64, c++....  All I do is use
strings and '\n'..  I get to use a large number of older sounds and
effects (for basic) on newer compilers that have aditional options..
It just looks like another music tracker..  I am not sure if that fits
what you are trying to do though.



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