examples/gallery/01-points.hero

## Points
#
# Records, their constructors, and UFCS. Every field is named at the call
# site, always — `Point(3, 4)` does not exist.

# A position on the integer grid.
record Point
    x: i64
    y: i64

# A rectangle, by two corners.
record Rect
    corner: Point
    extent: Point

# Squared distance. Avoids the square root to keep it exact.
#
# Both parameters are `Point`, so §4.9 makes the names mandatory at every call
# site: `a.dist2(b: c)` cannot be silently the other way round. That is the rule
# that spends tokens exactly where argument inversion happens.
function dist2(a: Point, b: Point) -> i64
    dx = a.x - b.x
    dy = a.y - b.y
    return dx * dx + dy * dy

# The point halfway between two others, rounded towards zero.
function midpoint(a: Point, b: Point) -> Point
    return Point(x: (a.x + b.x) / 2, y: (a.y + b.y) / 2)

function area(r: Rect) -> i64
    return r.extent.x * r.extent.y

# Reads as a sentence, and it is one function call: `translate(r, by)`.
function translate(r: Rect, by: Point) -> Rect
    moved = Point(x: r.corner.x + by.x, y: r.corner.y + by.y)
    return Rect(corner: moved, extent: r.extent)

test "the 3-4-5 triangle"
    assert dist2(a: Point(x: 0, y: 0), b: Point(x: 3, y: 4)) == 25

test "a rectangle keeps its size when it moves"
    unit = Rect(corner: Point(x: 0, y: 0), extent: Point(x: 2, y: 3))
    assert unit.translate(Point(x: 10, y: 10)).area() == unit.area()

function main()
    a = Point(x: 0, y: 0)
    b = Point(x: 3, y: 4)
    print("distance squared: ", a.dist2(b: b))
    print("midpoint x: ", a.midpoint(b: b).x)