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Diffstat (limited to 'AMSB.txt')
| -rw-r--r-- | AMSB.txt | 81 |
1 files changed, 79 insertions, 2 deletions
@@ -5,12 +5,20 @@ AMSB is actually a pretty cool BASIC for the Atari 8-bit. I never got the chance to use it 'back in the day' because it was expensive, required a floppy drive and at least 32K of RAM (my poor 400 had a tape drive for the first few years), and then later on, there was -Turbo BASIC XL, which was just as cool as AMSB, but freeware. +Turbo BASIC XL, which was cooler than AMSB, and also freeware. This file is a collection of notes I made to myself while developing listamsb. The information here might be useful (e.g. if you're trying to repair a damaged AMSB file) and hopefully is interesting. Enjoy! +This file is part of the bw-atari8-utils source. You can get the +latest version of the source from: + +https://slackware.uk/~urchlay/repos/bw-atari8-tools + +...which you can either view with a web browser or use with the 'git +clone' command. + -- B. Watson <urchlay@slackware.uk> @@ -75,6 +83,73 @@ depending on what version of AMSB you have, what DOS you boot, whether or not you have the R: device driver loaded, etc etc). +Redundant Tokens +---------------- + +There are two separate tokens each for PRINT and AT: + +token | text +------+----------------------- + $ab | "PRINT " + $ac | "PRINT" + $df | "AT(" + $e0 | "AT " + +When tokenizing a line, AMSB will actually use the $ab token if +there's a space after PRINT (or ?), otherwise it will use the +$ac token. These lines actually get tokenized differently: + +10 PRINT "HELLO" +10 PRINT"HELLO" + +Same applies to the $df and $e0 AT tokens: if the user entered +"AT(X,Y)", $df is used. Otherwise, with "AT (X,Y)", $e0 is used +(followed by an ASCII left parenthesis). + +3 tokens include the opening parenthesis: + +token | text +------+----------------------- + $d2 | "TAB(" + $d6 | "SPC(" + $df | "AT(" + +Normally in AMSB, it's OK to leave a space between a function name +and the left-paren. PEEK (123) and SIN (1) are both valid. However, +for SPC and TAB, no space is allowed, because the ( is part of the +token. AT would be the same way, except there's a separate token $e0 +that *includes* the space. Weird, huh? A side effect of this is +that "SPC (10)" or "TAB (10)" won't be treated as a function call. +Instead, the SPC or TAB is treated as a variable name. If you write: + +PRINT TAB (10);"HELLO" + +...it'll print " 0 HELLO" at the start of the line[*], instead of "HELLO" +in the 10th column as you might have expected. It also means that AT, +TAB, and SPC are valid variable names in AMSB, which is an exception +to the rule that keywords can't be used as variable names (e.g. SIN=1 +or STRING$="HELLO" are invalid). + +[*] Unless you've assigned another value to TAB, of couse. + + +Unused Tokens +------------- + +If you look at the token list in amsbtok.h (or in a hex dump +of the AMSB executable or cartridge image), you'll see a lot of +double-quotes mixed in with the list. AMSB doesn't actually tokenize +the " character (it's stored as $22, its ASCII value), so these seem +to be placeholders, either because some tokens were deleted from the +language during its development, or else they're intended for some +future version of AMSB that never happened. + +The weird quote tokens are $99, $c8 to $d0, $d5, and $e7 to $ed. If +you hexedit a program to replace a regular double-quote with one of +these tokens, it will list as either "" or just one ", but it will +cause a syntax error at runtime. + + LOADing Untokenized Files ------------------------- @@ -90,7 +165,9 @@ happen if a LISTed file somehow got truncated. While on the subject... the manual doesn't mention it, but if you LOAD a text file without line numbers, the code gets executed in direct mode during the load (like Atari BASIC's ENTER command does). This -means you could write scripts (batch files) for AMSB. +means you could write scripts (batch files) for AMSB... though you'd +be better off using MERGE, rather than LOAD (MERGE is basically the +same thing as Atari BASIC's ENTER). Program Length Header Mismatch |