    CALC:  Simple calculator program.

    The calc program computes the value of an arithmetic expression, and
    prints it on standard output.  Although this program may be useful, it
    was mostly written as a test of the formula module (see formula.doc).

    Usage:

        calc { var=formula } formula

    The value of the final formula is computed and printed.  This formula
    may contain references to variables that were assigned values in the
    earlier arguments.  These assignments are performed in order; the
    formulas they contain may reference variables that were assigned
    values earlier.  A variable name may be a single lower-case letter, or
    a lower-case letter followed by a single digit.

    For the syntax of formulas, see formula.doc.

    Some examples:

       > calc "3+5"
       8

       > calc "p=0.913" "100p(1-p)"
       7.9431

       > calc "x1=8.9E5" "x2=1.2E6" "Sqrt(x1*x2)"
       1.03344E+06

       > calc "x=4.8" "y=x+1.9" "z=y-3.1" "Exp { - (x^2+y^2+z^2) / 2 }"
       2.72245E-18

       > calc "s=3" "i=2" "n=10" "sin(4)"
       240

       Note that "sin(4)" is interpreted as "s*i*n*(4)"!
       "Sin(4)" would evaluate the sine of 4.

       > calc "1.3e4+12.1"
       Undefined variable: e4

       You have to use upper-case "E" for numbers in scientific notation.