YAUS ( Yet Another Useless Stuff )

YAUS is a very limited BASIC like interactive interpreter.

Note that the syntax of this language is fairly rigid. Extra white spaces are not allowed.
For example: "if a<b print a" is a valid expression, but "if a < b print a" or " if a<b  print  a" is not.
There is no relevant error checking because of the 512b limitation.

Variables:
==========
      All variable name must be one lowercase character from 'a' to 'z'.

      For example:
          a=123

      The variables are initialized to zero.

Types:
======
      This language supports only unsigned - one byte - integers. (Range: 0..255)

Operators:
==========

          =         assignment
          +         addition
          -         subtraction

Usage:
          variable1=variable2
          variable1=integer

          variable1+variable2
          variable1+integer

          variable1-variable2
          variable1-integer

          Note that 'a+b' means '+=' and 'a-b' means '-='.
          So the result will be stored in the first operand.

Exampe:
          a=12
          b=2
          a-b
          a+10  (a will be 20)

I/O commands:
=========
          print <variable>


Condition:
==========

          Syntax:
                  if <variable1><relation><variable2> <expression>
                  Valid relations are: <, >, =

          Examples:
                  if a>b print a
                  if a<b print a
                  if a=b print a

          Note:
                  Constants are not allowed in conditions: "if a>123" is invalid.
                  You have to store the value 123 in a second variable.

                  >=, <=, != are not implemented

Goto:
=====

          Syntax:
                  goto <rownumber>
          Example:
                  goto 105


Examples:

100 a=0
101 b=5
102 print a
103 a+1
104 if a<b goto 102

Output:
       1

       2

       3

       4


Calculate 3*4

100 a=3
101 b=4
102 c=0
103 e+a
104 b-1
105 if b>c goto 103

    print e           12

Note: Scrolling is not implemented because of the 512b limitation. If you run out of the display, reset the computer.