haskell for kids: stepping through algebraic formulas, even if aren't about numbers

Program:

(overlay/xy (overlay/xy (scale 10 (star 5 'solid 'blue))
                        -100 100
                        (scale 10 (star 5 'solid 'red)))
            -100 200
            (scale 10 (star 5 'solid 'yellow)))

Images from the stepper:





Matthias Felleisen