Variables and lists

Inside a block, define creates a variable. Unlike parameters, attributes and global constants, a variable can change: give it a new value with =, or add to a list with append:

define x = 0um
define xs: [size] = []
for i in 0..4 {
    xs.append(x)
    x = x + 10um
}
# xs is now [0, 10um, 20um, 30um]

A variable lives until the end of the block that defines it. Its type comes from its first value, so two cases need care:

• an empty list needs its type written out, [size], [point] and so on, since there is nothing to infer it from;
• a plain 0 is an integer: a length that starts at zero is 0um, or define x: size = 0.

Lists are indexed from 0 — xs[1] — and len(xs) is their length. polygon and path take lists of points, so a loop can build the outline of a shape point by point.