Documentation for @.COM
                  ~~~~~~~~~~~~~~~~~~~~~~~

     @.COM   is  an online expression evaluator  for  CP/M`s 
CCP.  I never had a calculator handy when I needed one  most 
,so  threw together this program and saved it on each of  my 
working disks.

     It  acts  as  a calculator in the same  manner  as  the 
calculator or immediate mode of BASIC. The expression may be 
included  in  the  command line or input  from  the  program 
itself.

     The expression evaluator package originally came in raw 
form from October 1978 Dr.  Dobb`s Journal - page 34 by Mike 
Gabrielson. It now requires CP/M to run (developed under CP/M 
2.2 on a DISCUS 2D/B).

     This  is  useful for machine language programming  with 
its  HEX arithmatic and Boolean operators.  The answers  are 
both in deciaml and hex.

     This demonstates evaluating an expression from  command 
level. After completion, the program returns control to CPM.

Ex-   A>@ #F-5    

      10(D)    000A(H) --->> program outputs this answer

      A> 
 
     But  if  we  just  enter  `@`  at  command  level,  the 
evaluator  will be brought up and expressions will be  input 
through a built in mini-editor. 

     Unlike entering the expression at command level ,  this 
alternative  allows you to remain in the evalutor to do many 
calcultions.

     To return to CP/M, type '^C' or just hit 'RETURN'.

Ex-   A>@

      (`?` for info.) --->> 1+2+3+4

      10(D)     0000A(H)

      (`?` for info.) --->>         -- note it doesnt return
                                       to CPM.
     
     A  short command summary is provided in the program  if 
you press `?` as the first character of the expression line. 
This will not work from the command level.

         Ex-  (`?` for info,) ?
              ---- instructions printed ----

Operators:
=-=-=-=-=

(    - precedence bracket (for expression nesting)
&    dyadic and
*    dyadic multiply
+    dyadic add or monadic plus
-    dyadic subtract or monadic negate (two`s complement)
/    dyadic divide
//   dyadic remainder
<    dyadic less than
>    dyadic greater than
<=   dyadic less then or equal
==   dyadic equal
>=   dyadic greater than or equal
<<   dyadic or monadic rotate left
>>   dyadic or monadic rotate right
|    dyadic inclusive OR
||   dyadic exclusive OR
~    monadic one`s complement
~=   dyadic not equal

Constants
=-=-=-=-=

     All constants are evaluated as 16 bit unsigned integers 
with overflow ignored.  The values may range from 0 to 65535 
decimal  or  0  to #FFFF hex and may be one or  all  of  the 
following types:

1) Decimals    - 12635
2) Hexadecimal - #F23D
3) Strings     - 'ABC'

Relational Operators
=-=-=-=-=-=-=-=-=-=-

     The  dyadic operators: == ~= <= >= < > are used to form 
expressions  that  evaluate to either zero or  one.  If  the 
relation is true,  the operators produce a result of one.  A 
false comparison results in zero:

      Expression       Evaluated result

 Ex-  5 == 5           1
      3+(2~=6)         4
      (1<=2)<=3        1
      #FFFF<0          0

     The  operators  <<  and >> can be  used  as  dyadic  or 
monadic  operators  to rotate (not shift) 16  bit  operands. 
Rotation  implies  wraparound  of  bits.   Shifting  can  be 
accomplished  with the multiply and divide  operators.  When 
used as monadic operators operands are rotated one bit. When 
used  as dyadic operators,  the first operand specifies  the 
number of bits to rotate.

 Ex-  <<2              4
      >>3              #8001
      >>(<<2)          2
      3>>#f0           #1E

String Operations
=-=-=-=-=-=-=-=-=

     If  a  string  constant appears in an  expression  with 
operators,  the value of the string is the ASCII code of the 
string`s first character.  An exception to this rule  occurs 
when  two strings appear with a relational operator: then  a 
character  by  character comparision of the two  strings  is 
performed, using the ASCII code to determine relative order. 
If  the two strings are of unequal length,  the  shorter  is 
padded on the right with blanks.

 Ex-   'A'+1            #42
       'ABC'&#FF        #41
       'CAT'<'dog'      1
       'PAD'=='PAD '    1
       '123'==#31       1

Closing
=-=-=-=

     This  is  a  hacked together program and has  not  been 
thoroughly tested.  If you find any bugs please pass them on 
to me via a `BBS` or other channel.

                                   Robert Lansdale