eval: command line calculator

Small (156 kB) command line calculator. Evaluate an expression directly from command line with
eval <expr> command
Example:
c:\> eval 2+3
5
or in an interactive session.
In a session, results may be assigned to unlimited number of variables and used in later calculations.

Example:
> x := 6+7
13.0000
>y := x*2
26.0000

Large number of elementary, special, trigonometric, hyperbolic and probability distribution functions are available.
Number of decimal digits is defined by assigning _decimal variable.