Subj : Something strange going on.
To   : All
From : Janne Johansson
Date : Fri Apr 13 2018 09:53:58

On 2018-04-11 02:33, Shaun Bebbington : All wrote:
> Hi,
>
> I found something odd today in the powerful CBM BASIC v2.0.
>
> Having worked with Sinclair BASIC quite a lot recently, I use GOTO X
> where X is a valid line number (i.e., LET X = 100). But I know that's
> not possible with Microsoft BASIC. Of course there is the ON X GO TO
> 100,200 ...
>
> So I thought "I know, I'll try and use a function, could CBM BASIC use
> this as a look up table". The following, I expected to go to the value
> in the function A() which returns 10, but...
>
> 0 DEF FN A(X) = 10
> 1 PRINT FN A(0)
> 2 GO TO FN A(0)
> 3 PRINT "END GRACEFULLY"
> 4 END
> 10 PRINT "STOP"
> 11 STOP
>
> Try it for yourself. What's going on here?

BTW, I got reminded of someone devising a way to make selfmodifying
BASIC on C64, by printing out the line you wanted to have, then moving
the cursor to that line on the screen, adding "RETURN" and R, U, N and
"RETURN" into the keyboard input buffer and telling the system the
buffer has 5 CHARS in it, then ending the program, whereupon the system
will enter that line you generated and then re-ran your program.

Of course you have to write it so it can restart nicely on the second
and upcoming runs, but with such a scheme, you could make a
10 GOTO <runtimegenerated line here>
thing actually work, at the cost of losing more or less all variables
and state of course.

But it was a nice trick.

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