COAET" • r

APPLESOFT PROGRAM FORMATTING LISTER
by David H. Bartley
If I = 1 A
PRlNT
11 IF A' T$ GOSIJB 4075 I
One of the handiest utilities for any language system is a
formatting lister, or "pretty-print" routine. Having been
spoiled by a good commercial Pascal pretty-printer on the
job, I decided that I had to write one for use with Applesoft
on the Apple at home. The built-in LIST command gives me
the information I need, but it sure doesn't go out of its way to
make it easy to read!
Most pretty-printers I'm familiar with are designed for
printer output. I wanted mine to create nice hard-copy listings,
but I also wanted to make it easier to display parts of a
program in the Apple's screen in a more readable form. The
Assembly language program in Listing 1 is the result of my
efforts to do just that.
Program Features
My pretty-print routine for Applesoft programs was
deveby loped adding the features listed below to the algorithm
used by BASIC. (The original code may be found by
disassembling from $D6A5 to $D765 in the ROM.)
1. The pretty-printer is easily initialized by typing "BRUN
A/5 LISTER" Formatted listings are then generated by
typing any of the LIST commands, preceded by an ampersand
( & ). The standard arguments (one line number, or two
separated by a comma, or dash), are allowed. The word
"LIST' may be abbreviated to "L." Output may be to the
printer, to the screen, or both.
2. All program line numbers are displayed right-adjusted
in the first five output columns. All program statements
begin in Column 7.
3. Each statement separator(:) appearing past Column
12 causes a line break. The ":" is displayed in Column 4 of
the following output line.
4. Lines usually extend to Column 38 instead of 33. The
continuation of a long line is indented three extra spaces.
5. Each output line is indented an extra two spaces for
each level of nested FOR. .. NEXT and IF. .. THEN statements.
To avoid squeezing too closely against the right margin,
indentation stops at Column 30.
6. A space is listed after every comma or semicolon
(except those in REMs and quoted strings).
7. The output line is broken and continued whenever a
space, comma, or semicolon appears past Column 33.
8. No extra blanks are displayed around the " *" and ()
tokens.
9. A blank is not listed before a keyword if the previous
character is a blank or left parenthesis.
10. A blank is not listed after a keyword ending with a
parenthesis (such as "TAB('', for example).
11. Non-printing control characters are listed as letters
enclosed within square brackets.
12. The listing can be temporarily stopped and then
resumed by hitting any key. Control-C may be used to
cancel the listing.
Operational Requirements
There are a few things you need to be aware of, however.
A/S LISTER must be used under DOS with Applesoft in
ROM (or at the same locations in RAM card). It is not hidden
above HIMEM, so it may be wiped out if your program or its
data requires too much space. Another point: the"&" vector
is used to enable RENUMBER; if you're using that utility
while coding, you can't use the Lister, and vice versa.
There is one known bug: it doesn't realize that "NEXT J,J"
ends two FOR. .. NEXT loops instead of one; the indentation
will be slightly off. Since it's better programming practice to
use "NEXT I: NEXT J," I haven't made provision for the
sloppier form.
The Assembly language program in Listing 1 should be
assembled and placed in the binary file "A/ S LISTER."
BRUNning that file loads the program in the Apple's
memory at location $6000 Uust above Hi-Res Page 2), and
sets up the ampersand vector. (Obviously, the ampersand
vector can't be used for more than one purpose at a time.)
Once loaded and initialized with BRUN, the program may
be invoked with " & LIST' any number of times.
36 Apple Orchard