Example for versions Factor 0.94

Word `quadratic-equation` takes coefficients of the equation as input and prints the solution while returning nothing. Note that this word is declared using token `::` instead of `:` used in most cases; this means that within it lexically scoped variables can be used, in this case parameters `a`, `b` and `c` as well as local variables `d`, `x0` and `sd` bound by `:>` operator. Such variables can be loaded on the stack using their names. Words and operators which process lexically scoped variables are available in dictionary `locals`.

Factor provides a built-in data type for complex numbers; whenever the discriminant is negative, its square root will be of type `complex`. In this case complex roots are printed using words `real-part` and `imaginary-part` which extract corresponding parts of a number.

`readln` reads a string from input stream (till the end of line), and `string>number` (from `math.parser` dictionary) converts a string to a floating-point number.

``````USING: formatting io kernel locals math math.functions math.parser ;

:: quadratic-equation ( a b c -- )
a 0 =
[ "Not a quadratic equation." printf ]
[ b sq a c * 4 * - :> d
b neg a 2 * / :> x0
d sqrt a 2 * / :> sd
d 0 =
[ x0 "x = %f\n" printf ]
[ d 0 >
[ x0 sd + x0 sd - "x1 = %f\nx2 = %f\n" printf ]
[ x0 sd + [ real-part ] [ imaginary-part ] bi "x1 = (%f, %f)\n" printf
x0 sd - [ real-part ] [ imaginary-part ] bi "x2 = (%f, %f)\n" printf ]
if
]
if
]
if ;