$CPU 8086                 ' program works on any CPU
$OPTIMIZE SIZE            ' make smallest possible executable
 $COMPILE UNIT            ' compile to an EXE
'$COMPILE EXE             ' compile to an EXE

$DEBUG MAP OFF            ' turn off map file generation
$DEBUG PBDEBUG OFF        ' don't include pbdebug support in our executable


$COM    0                 ' set communications buffer to nothing
$STRING 16                ' set largest string size at 16k
$STACK  2048              ' let's use a 2k stack
$SOUND  1                 ' smallest music buffer possible

$DIM ARRAY                ' force arrays to be pre-dimensioned before they can
                          ' be used
$DYNAMIC                  ' all arrays will be dynamic by default

DEFINT A-Z                ' default all variables to integers for maximum
                          ' speed and minimum size

'Evaluate - Evaluates a given expression and returns answer
'-------------------------------------------------------------------------
' EVAL(STRING$,ERRCODE%)
'     Evaluate math formula.
'     Returns a double precision number calculated from STRING$.  If an
'     error occurs, ERRCODE% will be greater than 0.
'     EXAMPLE:  T# = EVAL("2*(3*3)",E)     18
'-------------------------------------------------------------------------
FUNCTION EVAL(BYVAL Expr$,ErrCode AS INTEGER) PUBLIC AS DOUBLE

  Expr$ = UCASE$(Expr$)

  'Tokenize the multi-charactor operators
  REPLACE "[" WITH "(" IN Expr$           'parenthesis
  REPLACE "]" WITH ")" IN Expr$           'parenthesis
  REPLACE "{" WITH "(" IN Expr$           'parenthesis
  REPLACE "}" WITH ")" IN Expr$           'parenthesis
  REPLACE "X" WITH "*" IN Expr$           'multiplication
  REPLACE "#"  WITH "!" IN Expr$          'not equal
  REPLACE "<>" WITH "!" IN Expr$          'not equal
  REPLACE ">=" WITH ";" IN Expr$          'greater than or equal
  REPLACE "=>" WITH ";" IN Expr$          'greater than or equal
  REPLACE "<=" WITH ":" IN Expr$          'less than or equal
  REPLACE "=<" WITH ":" IN Expr$          'less than or equal
  REPLACE "**" WITH "^" IN Expr$          'to the power of
  REPLACE "AND" WITH "&" IN Expr$         'AND
  REPLACE "XOR" WITH "$" IN Expr$         'XOR
  REPLACE "OR"  WITH "|" IN Expr$         'OR
  REPLACE "MOD" WITH "%" IN Expr$         'MOD
  REPLACE "-+" WITH "-" IN Expr$          'remove positive sign in subtraction

  Expr$ = REMOVE$(Expr$, " ")

  X = TALLY(Expr$,"(")
  Y = TALLY(Expr$,")")
  IF X<>Y THEN
    ErrCode = 1   'non-matching parenthesis
    EXIT FUNCTION
  END IF

  IF TALLY(Expr$,ANY "0123456789.()*/\%+-&|!$^=<>;:HODBACEF")<>LEN(Expr$) THEN
    ErrCode = 2   'invalid charactors
    EXIT FUNCTION
  END IF

  IF Y > 0 THEN
    X = INSTR(Expr$, ")")
    WHILE X > 0
      IF INSTR(Expr$, "()") THEN
        ErrCode = 3  'mismatched parenthesis
        EXIT FUNCTION
      END IF
      FOR I = X  TO 1 STEP -1
        IF MID$(Expr$, I, 1) = "(" THEN
          EXIT FOR
        END IF
      NEXT I
      IF I = 0 THEN
        ErrCode = 3  'mismatched parenthesis
        EXIT FUNCTION
      END IF
      Tmp$ = MID$(Expr$, I+1, X-(I+1))
      Ans$ = Answer$(Tmp$, ErrCode)
      IF ErrCode THEN
        EXIT FUNCTION
      END IF
      REPLACE "("+Tmp$+")" WITH Ans$ IN Expr$
      X = INSTR(Expr$, ")")
    WEND
  END IF

  X = TALLY(Expr$, ANY "*/\%+-&|!$^=<>;:XHODBACEF")
  WHILE X > 0
    IF (X = 1) AND (LEFT$(Expr$, 1) = "-") THEN
      EXIT DO
    END IF
    Expr$ = Answer$(Expr$, ErrCode)
    IF ErrCode THEN
      EXIT FUNCTION
    END IF
    X = TALLY(Expr$, ANY "*/\%+-&|!$^=<>;:XHODBACEF")
  WEND

  FUNCTION = VAL(Expr$)

END FUNCTION


FUNCTION Answer$(BYVAL Expr$, ErrCode AS INTEGER) PRIVATE

  X = TALLY(Expr$, ANY "*/\%+-&|!$^=<>;:XHODBACEF")
  WHILE X > 0
    Rp$ = ""
    IF (X = 1) AND (LEFT$(Expr$, 1) = "-") THEN
      EXIT DO
    END IF
    IF INSTR(Expr$, ANY "HODB") THEN
      T = INSTR(Expr$, ANY "HODB")
      Tmp$ = MID$(Expr$, T)
      T$ = EXTRACT$(Tmp$, ANY "*/\%+-()&|!^;:<>=")
      T = ASCII(T$)
      IF T = 72 OR T = 79 OR T = 66 THEN
        Rp$ = LTRIM$( STR$( VAL("&"+T$) ) )
      ELSEIF T = 68 THEN
        Rp$=MID$(T$,2)
      END IF
      REPLACE T$ WITH Rp$ IN Expr$
      Sign$ = ""
    ELSEIF INSTR(Expr$,"*") THEN
      Sign$ = "*"
    ELSEIF INSTR(Expr$,"/") THEN
      Sign$ = "/"
    ELSEIF INSTR(Expr$,"\") THEN
      Sign$ = "\"
    ELSEIF INSTR(Expr$,"%") THEN
      Sign$ = "%"
    ELSEIF INSTR(Expr$,"^") THEN
      Sign$ = "^"
    ELSEIF INSTR(Expr$,"+") THEN
      Sign$ = "+"
    ELSEIF INSTR(Expr$,"-")>1 THEN
      Sign$ = "-"
    ELSEIF INSTR(Expr$,"&") THEN
      Sign$ = "&"
    ELSEIF INSTR(Expr$,"|") THEN
      Sign$ = "|"
    ELSEIF INSTR(Expr$,"!") THEN
      Sign$ = "!"
    ELSE
      ErrCode = 4  'Error
      EXIT FUNCTION
    END IF
    IF ErrCode > 0 THEN
      EXIT FUNCTION
    END IF
    IF LEN(Sign$) > 0 THEN
      Tmp$ = GetValues(Expr$, Sign$, Number1#, Number2#, ErrCode)
      Rp$ = Result$(Sign$, Number1#, Number2#)
      REPLACE Tmp$ WITH Rp$ IN Expr$
    END IF
    X = TALLY(Expr$, ANY "*/\%+-&|!$^=<>;:XHODBACEF")
  WEND

  Answer$ = Expr$

END FUNCTION


FUNCTION GetValues$(BYVAL Expr$, BYVAL Sign$, Number1#, Number2#, ErrCode AS INTEGER)
  Position = INSTR(Expr$, Sign$)
  IF Position = 1 THEN
    IF INSTR("+-", Sign$) = 0 THEN
      ErrCode = 5  'expression error
      EXIT FUNCTION
    END IF
    Position = INSTR(2, Expr$, Sign$)
  END IF

  Tmp1$ = LEFT$(Expr$, Position - 1)
  Tmp2$ = MID$(Expr$, Position + 1)
  IF INSTR(Tmp2$, ANY "+-") = 1 THEN
    Position = 2
  ELSE
    Position = 1
  END IF

  FOR I = LEN(Tmp1$) TO 1 STEP -1
    IF INSTR(MID$(Tmp1$, I, 1), ANY"1234567890.") = 0 THEN
      EXIT FOR
    END IF
  NEXT I

  IF I = LEN(Tmp1$) THEN
    ErrCode = 5  'expression error
    EXIT FUNCTION
  END IF

  IF I = 1 THEN
    DECR I
  ELSEIF I > 1 THEN
    IF INSTR("+-", MID$(Tmp1$, I))>0 THEN
      IF INSTR("1234567890.", MID$(Tmp1$, I-1))=0 THEN
        DECR I
      END IF
    END IF
  END IF
  Tmp1$ = MID$(Tmp1$, I+1)

  FOR I = 1 TO LEN(Tmp2$)
    IF INSTR(MID$(Tmp2$, I, 1), ANY "1234567890.") = 0 THEN
      EXIT FOR
    END IF
  NEXT I
  IF I = 1 THEN
    ErrCode = 5  'expression error
    EXIT FUNCTION
  END IF
  Tmp2$ = LEFT$(Tmp2$, I-1)

  Number1# = VAL(Tmp1$)
  Number2# = VAL(Tmp2$)
  GetValues$ = Tmp1$ + Sign$ + Tmp2$

END FUNCTION


FUNCTION Result$(BYVAL Operation$, Number1#, Number2#) PRIVATE
  SELECT CASE Operation$
    CASE "+"
      Temp# = Number1# + Number2#
    CASE "-"
      Temp# = Number1# - Number2#
    CASE "/"
      Temp# = Number1# / Number2#
    CASE "\"
      Temp# = Number1# \ Number2#
    CASE "*", "X"
      Temp# = Number1# * Number2#
    CASE "^"
      Temp# = Number1# ^ Number2#
    CASE "%"
      Temp# = Number1# MOD Number2#
    CASE "&"
      Temp# = Number1# AND Number2#
    CASE "|"
      Temp# = Number1# OR Number2#
    CASE "$"
      Temp# = Number1# XOR Number2#
    CASE "<"
      Temp# = ABS(Number1# < Number2#)
    CASE ">"
      Temp# = ABS(Number1# > Number2#)
    CASE "="
      Temp# = ABS(Number1# > Number2#)
    CASE "!"
      Temp# = ABS(Number1# <> Number2#)
    CASE ";"
      Temp# = ABS(Number1# => Number2#)
    CASE ":"
      Temp# = ABS(Number1# <= Number2#)
    CASE ELSE
      Temp# = 0
  END SELECT

  Result$ = LTRIM$( STR$(Temp#) )

END FUNCTION
'/*-----------------------------------------------------------------
'  PRINT "Eval 1.0á þ Command Line Expression Evaluator"
'  PRINT "Copyright (c) 1994 Dave Navarro, Jr.        All Rights Reserved."
'  PRINT ""
'
'  INPUT EXPR$
'  'Expr$ = Trim$(UCASE$(COMMAND$))
'
'  IF (LEN(Expr$) = 0) OR (INSTR(Expr$,"?") > 0) THEN
'    PRINT "Usage:           EVAL expression"
'    PRINT ""
'    PRINT "         Where expression is a valid mathematical equation"
'    PRINT "         allowing for parenthetical precidence."
'    PRINT ""
'    PRINT "Example:         EVAL 4 + 5 * (4 + 9) / 6"
'    PRINT ""
'    PRINT "Supports:        * / + -     Multiplication, Division, Addition,"
'    PRINT "                             and subtraction."
'    PRINT "                 \ %         Integer Division, Modulus."
'    PRINT "                 ** ^        Raising to the power of."
'    PRINT "                 & | $       Logical AND, OR, and XOR."
'    PRINT "                 =< => <>    Less than or Equal to, Greater than"
'    PRINT "                             or Equal to, and Not Equal to."
'    PRINT "                 < > =       Less than, Greater than, and Equal"
'    PRINT "                             to."
'    END 1
'  END IF
'
'  PRINT EXPR$ + " ="
'
'  TMP# = EVAL(EXPR$, ERRCODE)
'
'  IF ERRCODE = 0 THEN
'    PRINT STR$(TMP#)
'  ELSE
'    PRINT "ERROR "+STR$(ERRCODE)+"!"
'    BEEP
'  END IF
'  INPUT Z
'  END ERRCODE
'