bas - basic
bas [ file ]
Bas is a dialect of Basic. If a file argument is provided, the file is used for input
before the terminal is read. Bas accepts lines of the form:
Integer numbered statements (known as internal statements) are stored for later execution.
They are stored in sorted ascending order. Non-numbered statements are immediately exe-
cuted. The result of an immediate expression statement (that does not have `=' as its
highest operator) is printed. Interrupts suspend computation.
Statements have the following syntax:
The expression is executed for its side effects (assignment or function call) or for
printing as described above.
This statement is ignored. It is used to interject commentary in a program.
Return to system level.
The name and current value of every variable is printed.
The UNIX editor, ed, is invoked with the file argument. After the editor exits, this
file is recompiled.
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 incremented by one on each loop, not to exceed
the value of the second expression.
The expression is evaluated, truncated to an integer and execution goes to the corre-
sponding integer numbered statment. If executed from immediate mode, the internal
statements are compiled first.
if expression statement
The statement (first form) or group of statements (second form) is executed if the
expression evaluates to non-zero. In the second form, an optional else allows for a
group of statements to be executed when the first group is not.
list [expression [expression]]
is used to print out the stored internal statements. If no arguments are given, all
internal statements are printed. If one argument is given, only that internal state-
ment is listed. If two arguments are given, all internal statements inclusively
between the arguments are printed.
The list of expressions and strings are concatenated and printed. (A string is
delimited by " characters.)
Prompt is the same as print except that no newline character is printed.
The expression is evaluated and the result is passed back as the value of a function
call. If no expression is given, zero is returned.
The internal statements are compiled. The symbol table is re-initialized. The ran-
dom number generator is reset. Control is passed to the lowest numbered internal
save [expression [expression]]
Save is like list except that the output is written on the file argument. If no
argument is given on the command, b.out is used.
Expressions have the following syntax:
A name is used to specify a variable. Names are composed of a letter 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 written in Fortran
style, and contains digits, an optional decimal point, and possibly a scale factor
consisting of an e followed by a possibly signed exponent.
( expression )
Parentheses are used to alter normal order of evaluation.
The result is the negation of the expression.
expression operator expression
Common functions of two arguments are abbreviated by the two arguments separated by
an operator denoting the function. A complete list of operators is given below.
expression ( [expression [ , expression] ... ] )
Functions of an arbitrary number of arguments can be called by an expression followed
by the arguments in parentheses separated by commas. The expression evaluates to the
line number of the entry of the function in the internally stored statements. This
causes the internal statements to be compiled. If the expression evaluates negative,
a builtin function is called. The list of builtin functions appears 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. 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. Assignment binds right to left,
& | & (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 i -th actual parameter on the current level of function call.
exp(x) is the exponential function of x.
log(x) is the natural logarithm of x.
sqr(x) is the square root 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. Its value is between -n/2 and n/2.
rnd( ) is a uniformly distributed random number between zero and one.
is the only form of program input. A line is read from the input and evaluated as
an expression. The resultant value is returned.
abs(x) is the absolute value of x.
int(x) returns x truncated (towards 0) to an integer.
b.out save file
/bin/ed for edit
Syntax errors cause the incorrect line to be typed with an underscore where the parse
failed. All other diagnostics are self explanatory.
Has been known to give core images.
Catches interrupts even when they are turned off.