Rebol3 Code Examplex

Rebol [
    title: "Rosetta code: Pentagram"
    file:  %Pentagram.r3
    url:   https://rosettacode.org/wiki/Pentagram
    needs: blend2d ;= for the draw command
]

canvas: 500x500
center: canvas / 2
radius: 200

points: collect [
    repeat vertex 10 [
        angle: vertex * 36 + 18 ;-- +18 is required for pentagram rotation
        either vertex % 2 = 1 [
            keep as-pair
                (cosine angle) * radius + center/x
                (sine   angle) * radius + center/y
        ][
            keep as-pair
                (cosine angle) * radius * 0.382 + center/x
                (sine   angle) * radius * 0.382 + center/y
        ]
    ]
]
img: draw canvas compose/deep [   
    fill-pen mint
    polygon (points)
    line-width 3        
    line (points/1) (points/5) (points/9) (points/3) (points/7) (points/1)
]
try [save %pentagram.png img]
try [view img]