The type for structured keys.

empty is the empty key. It refers to the top-level dictionary.

v s is the string s as a key. A key "/foo/bar" is decomposed into the segments "foo" and "bar". The initial "/" is always ignored so "foo/bar" and "/foo/bar" are equal.

add t s is the concatenated key t/s. Raise Invalid_argument if s contains "/".

t / x is add t x.

append x y is the concatenated key x/y.

x // y is append x y.

segments t is t's list of segments.

basename t is the last segment of t. basename empty is the empty string "".

parent t is the key without the last segment. parent empty is empty.

For any t, the invariant have parent t / basename t is t.

The comparison function for keys.

The equality function for keys.

The pretty printer for keys.

to_string t is the string representation of t. "/" is used as separator between segements and it always starts with "/".