calc/help/eval

NAME
    eval - evaluate a string

SYNOPSIS
    eval(str)

TYPES
    str		string

    return	any

DESCRIPTION
   For eval(str), the value of str is to be a string that could be the body
   of the definition of a function f().  This string may declare local
   variables and include keywords (while, for, ...) other than the
   reserved keywords (define, show, help, read, write, show, cd) intended
   for interactive use or for reading from a file.

   If str is the empty string "", eval(str) returns the null value.

   The call to eval(str) may return a value by explicit use of a return
   statement: "return;" returns the null value, "return expr;" returns the
   value of expr.  If execution reaches the end of str and the
   value on the execution stack is not null, eval(str) returns that value;
   otherwise eval(str) returns the most recently saved value.

   Each time eval(str) is called, a temporary function is compiled from
   the commands in str, and if there are no syntax errors, this function
   is then evaluated.  If str contains syntax errors, eval(str) displays
   the scanerror messages and returns the value error(49).

EXAMPLE
   > str1 = "2 + 3"; print eval(str1);
   5

   > i = 10; str2 = "local i = 0; 7; while (i++ < 5) print i^2,:;"
   > print i, eval(str2), i
   10 1 4 9 16 25 7 10

   (The print statements in str2 return the null value, so execution of
   eval(str2) ends by returning the saved value 7.  The global variable
   i is unchanged.)

   > eval("2 + ");
   Missing expression
	49

LIMITS
   The string str in eval(str) should not include a call to itself as in

	str = "2 + eval(str)"

   For this str, eval(str) causes an "Evaluation stack depth exceeded" error.
   Similarly, if str1 = "2 + eval(str2)", str2 should not include a call
   to eval(str1), etc.

LIBRARY
   none

SEE ALSO
    command, expression, define, prompt