BAS (I)                      1/15/73                      BAS (I)

NAME            bas -- basic

SYNOPSIS        bas [ file ]

DESCRIPTION     bas is a dialect of basic [1].  If a file argu-

                ment is provided, the file is used for input be-

                fore the console is read.

                bas accepts lines of the form:


                   integer statement

                Integer numbered statements (known as internal

                statements) are stored for later execution.  They

                are stored in sorted ascending order.  Non-

                numbered statements are immediately executed.

                The result of an immediate expression statement

                (that does not have '=' as its highest operator)

                is printed.

                Statements have the following syntax:


                      The expression is executed for its side ef-

                      fects (assignment or function call) or for

                      printing as described above.


                      Return to system level.

                   draw expression expression expression

                      A line is drawn on the Tektronix 611 dis-

                      play (/dev/vt0) from the current display

                      position to the XY co-ordinates specified

                      by the first two expressions.  (The scale

                      is zero to one in both X and Y directions)

                      If the third expression is zero, the line

                      is invisible.  The current display position

                      is set to the end point.

                   display list

                      The list of expressions and strings is con-

                      catenated and displayed (i.e. printed) on

                      the 611 starting at the current display po-

                      sition.  The current display position is

                      not changed.


                      The 611 screen is erased.

                   for name = expression expression statement

                   for name = expression expression



                      The for statement repetitively executes a

                      statement (first form) or a group of state-

                      ments (second form) under control of a

                      named variable.  The variable takes on the

                      value of the first expression, then is in-

                      cremented by one on each loop, not to ex-

                      ceed the value of the second expression.

                   goto expression

                      The expression is evaluated, truncated to

                      an integer and execution goes to the corre-

                      sponding integer numbered statment.  If ex-

                      ecuted from immediate mode, the internal

                      statements are compiled first.

                   if expression statement

                      The statement is executed if the expression

                      evaluates to non-zero.

                   list [expression [expression]]

                      list is used to print out the stored inter-

                      nal statements.  If no arguments are given,

                      all internal statements are printed.  If

                      one argument is given, only that internal

                      statement is listed.  If two arguments are

                      given, all internal statements inclusively

                      between the arguments are printed.

                   print list

                      The list of expressions and strings are

                      concatenated and printed.  (A string is de-

                      limited by " characters.)

                   return [expression]

                      The expression is evaluated and the result

                      is passed back as the value of a function

                      call.  If no expression is given, zero is



                      The internal statements are compiled.  The

                      symbol table is re-initialized.  The random

                      number generator is re-set.  Control is

                      passed to the lowest numbered internal


                Expressions have the following syntax:


                      A name is used to specify a variable.

                      Names are composed of a letter ('a' - 'z')

                      followed by letters and digits.  The first

                      four characters of a name are significant.


                      A number is used to represent a constant

                      value.  A number is composed of digits, at

                      most one decimal point ('.')  and possibly

                      a scale factor of the form e digits or e-


                   ( expression )

                      Parentheses are used to alter normal order

                      of evaluation.

                   expression operator expression

                      Common functions of two arguments are ab-

                      breviated by the two arguments separated by

                      an operator denoting the function.  A com-

                      plete list of operators is given below.

                   expression ( [expression [, expression ...]] )

                      Functions of an arbitrary number of argu-

                      ments can be called by an expression fol-

                      lowed by the arguments in parentheses sepa-

                      rated by commas.  The expression evaluates

                      to the line number of the entry of the

                      function in the internally stored state-

                      ments.  This causes the internal statements

                      to be compiled.  If the expression evalu-

                      ates negative, a builtin function is

                      called.  The list of builtin functions ap-

                      pears below.

                   name [ expression [, expression ...] ]

                      Each expression is truncated to an integer

                      and used as a specifier for the name.  The

                      result is syntactically identical to a

                      name.  a[1,2] is the same as a[1][2].  The

                      truncated expressions are restricted to

                      values between 0 and 32767.

                The following is the list of operators:


                      = is the assignment operator.  The left

                      operand must be a name or an array element.

                      The result is the right operand.  Assign-

                      ment binds right to left, all other opera-

                      tors bind left to right.

                   & |

                      & (logical and) has result zero if either

                      of its arguments are zero.  It has result

                      one if both its arguments are non-zero.  |

                      (logical or) has result zero if both of its

                      arguments are zero.  It has result one if

                      either of its arguments are non-zero.

                   < <= > >= == <>

                      The relational operators (< less than, <=

                      less than or equal, > greater than, >=

                      greater than or equal, == equal to, <> not

                      equal to) return one if their arguments are

                      in the specified relation.  They return

                      zero otherwise.  Relational operators at

                      the same level extend as follows: a>b>c is

                      the same as a>b&b>c.

                   + -

                      Add and subtract.

                   * /

                      Multiply and divide.



                The following is a list of builtin functions:


                      Arg(i) is the value of the ith actual pa-

                      rameter on the current level of function



                      Exp(x) is the exponential function of x.


                      Log(x) is the logarithm base e of x.


                      Sin(x) is the sine of x (radians).


                      Cos(x) is the cosine of x (radians).


                      Atn(x) is the arctangent of x.


                      Rnd() is a uniformly distributed random

                      number between zero and one.


                      Expr() is the only form of program input.

                      A line is read from the input and evaluated

                      as an expression.  The resultant value is



                      Int(x) returns x truncated to an integer.

FILES           /tmp/btm?       temporary

SEE ALSO        [1] DEC-11-AJPB-D

DIAGNOSTICS     Syntax errors cause the incorrect line to be

                typed with an underscore where the parse failed.

                All other diagnostics are self explanatory.

BUGS            --