struct Material {
  diameter: Length,
  density: MassDensity,
  price: Money / Mass,
}

let PLA = Material {
  diameter: 1.75 mm,
  density: 1.27 g/cm^3,
  price: 16.99 €/kg,
}

fn print_cost(material: Material, mass: Mass) -> Money = material.price × mass

fn filament_length(material: Material, mass: Mass) -> Length = volume / cross_section -> meter
  where r = material.diameter / 2
    and cross_section: Area = π r²
    and volume: Volume = mass / material.density


# Print parameters
let mass_model = 80 g
let material = PLA

print("Mass of model:   {mass_model}")
print("Filament length: {filament_length(material, mass_model):.2}")
print("Cost of model:   {print_cost(material, mass_model):.2}")