A note on the indentation syntax.

: (colon) starts a new indentation block, like "let", "of" or "where" in Haskell.
Each line in an indentation block is considered as an block item.
If a block item consists of 2 or more elements, they are automatically parenthesized.

For example:

foo:
  bar
  baz quux
  zot

means

foo
  bar
  (baz quux)
  zot

.

Note that the entire block is not parenthesized.

As in Haskell, you can continue a block item by indenting more.

. (dot) acts like an opening parenthesis, but lacks a matching closing parenthesis.
Its scope extends to the right as far as possible, before hitting a closing parenthesis
or the end of a block item the dot belongs to.

Example:

(foo . bar baz)

means

(foo (bar baz))

Also:

.:
def a . + b c
def z . do:
  x = 3
  + x x

means

((def a (+ b c))
 (def z
  (do
    (x = 3)
    (+ x x))))