_                 _  ______  ___   _____ _____ _____ 
| |               | | | ___ \/ _ \ /  ___|_   _/  __ \
| |__   ___   ___ | |_| |_/ / /_\ \\ `--.  | | | /  \/
| '_ \ / _ \ / _ \| __| ___ \  _  | `--. \ | | | |    
| |_) | (_) | (_) | |_| |_/ / | | |/\__/ /_| |_| \__/\
|_.__/ \___/ \___/ \__\____/\_| |_/\____/ \___/ \____/

bootBASIC interpreter in 512 bytes (boot sector, ROM BIOS or COM file)
by Oscar Toledo G. Jul/22/2019

http://nanochess.org
https://github.com/nanochess

This is an integer BASIC language interpreter.

It's compatible with the 8088 processor (the original IBM PC). 

If you want to assemble it, you must download the Netwide Assembler
(nasm) from www.nasm.us

Use this command line:

  nasm -f bin basic.asm -Dcom_file -o basic.com
  nasm -f bin basic.asm -Dbootsect -o basic.img

To create a ROM image, you need to calculate the checksum. To do this,
there is a program addchecksum. It can be compiled with the gcc
compiler. As a result, the assembly of the ROM image will look
like this:

  gcc addchecksum.c -o addchecksum
  nasm -f bin basic.asm -Dbootrom -o basic.rom
  ./addchecksum basic.rom || rm basic.rom

Tested with VirtualBox for Mac OS X running Windows XP running this
interpreter, it also works with DosBox and probably with qemu:

  qemu-system-x86_64 -fda basic.img

or

  qemu-system-i386  -net none -option-rom basic.rom

for ROM BIOS.

Enjoy it!


 _   _             _      __  __                    _ 
| | | |___ ___ _ _( )___ |  \/  |__ _ _ _ _  _ __ _| |
| |_| (_-</ -_) '_|/(_-< | |\/| / _` | ' \ || / _` | |
 \___//__/\___|_|   /__/ |_|  |_\__,_|_||_\_,_\__,_|_|

        
Line entry is done with keyboard, finish the line with Enter.
Only 19 characters per line as maximum.
        
Backspace can be used, don't be fooled by the fact
that screen isn't deleted (it's all right in the buffer).
        
All statements must be in lowercase.

Line numbers can be 1 to 999.

26 variables are available (a-z)

Numbers (0-65535) can be entered and display as unsigned.
       
To enter new program lines:
  10 print "Hello, world!"
        
To erase program lines:
  10
        
To test statements directly (interactive syntax):
  print "Hello, world!"
        
To erase the current program:
  new
        
To run the current program:
  run
        
To list the current program:
  list
        
To exit to command-line:
  system
        
Statements:
  var=expr        Assign expr value to var (a-z)
        
  print expr      Print expression value, new line
  print expr;     Print expression value, continue
  print "hello"   Print string, new line
  print "hello";  Print string, continue
        
  input var       Input value into variable (a-z)
        
  goto expr       Goto to indicated line in program
        
  if expr1 goto expr2
              If expr1 is non-zero then go to line,
              else go to following line.
        
Examples of if:
        
  if c-5 goto 20  If c isn't 5, go to line 20
        
Expressions:
        
  The operators +, -, / and * are available with
  common precedence rules and signed operation.
  Integer-only arithmetic.
        
  You can also use parentheses:
        
     5+6*(10/2)
        
  Variables and numbers can be used in expressions.

  The rnd function (without arguments) returns a
  value between 0 and 255.
        
Sample program (counting 1 to 10):
        
10 a=1
20 print a
30 a=a+1
40 if a-11 goto 20
        
Sample program (Pascal's triangle, each number is the sum
of the two over it):
        
10 input n
20 i=1
30 c=1
40 j=0
50 t=n-i
60 if j-t goto 80
70 goto 110
80 print " ";
90 j=j+1
100 goto 50
110 k=1
120 if k-i-1 goto 140
130 goto 190
140 print c;
150 c=c*(i-k)/k
160 print " ";
170 k=k+1
180 goto 120
190 print
200 i=i+1
210 if i-n-1 goto 30

Sample program of guessing the dice:

10 print "choose ";
20 print "a number ";
30 print "(1-6)"
40 input a
50 b=rnd
60 b=b-b/6*6
70 b=b+1
80 if a-b goto 110
90 print "good"
100 goto 120
110 print "miss"
120 print b


>> LINKS <<

Taisuke Fukuno made a 64-bit version of bootBASIC for
Mac OS X, a small article about it is available at:

    https://fukuno.jig.jp/2853

  Source code:
    https://github.com/taisukef/bootBASIC_64bit


>> ATTENTION <<        

Do you would like more details on the inner workings? This program
is fully commented in my new book Programming Boot Sector Games
and you'll also find a 8086/8088 crash course!

Now available from Lulu:

  Soft-cover
    http://www.lulu.com/shop/oscar-toledo-gutierrez/programming-boot-sector-games/paperback/product-24188564.html

  Hard-cover
    http://www.lulu.com/shop/oscar-toledo-gutierrez/programming-boot-sector-games/hardcover/product-24188530.html

  eBook
    https://nanochess.org/store.html

These are some of the example programs documented profusely
in the book:

  * Guess the number.
  * Tic-Tac-Toe game.
  * Text graphics.
  * Mandelbrot set.
  * F-Bird game.
  * Invaders game.
  * Pillman game.
  * Toledo Atomchess.
  * bootBASIC language.