[O'Caml-tip] This is seriously cool

[wtd]

Just piced this one up from comp.lang.functional.

Let's say I want to copy a structure, but want to change one member.

For starters, the structure describes a point in three-dimensions.

code:

type point3d = { x : int; y : int; z : int }

Now I define one point:

code:

let first_point = { x = 1; y = 6; z = 42 }

Now I want to copy the first point into a second point, but zero the z coordinate. The lengthy (and thus more error-prone) method is:

code:

let second_point = {x = first_point.x; y = first_point.y; z = 0 }

Instead, how about...

code:

let second_point = { first_point with z = 0 }