seqable

[ seq\init:, seq\next: ]

The seqable protocol defines how a value can produce a lazy sequence of other values.

To use the seqable protocol, begin by sending seq\init:

  (ok next values*) = ['1' '2' '3' '4'].seq\init

ok will contain ok: or none:. This determines whether or not the sequence had an initial value.

It follows that empty sequences return none: when seq\init is sent.

Non-empty sequences will return ok:, followed by next (more on that later), followed by a run of values.

The run of values can be any number of values. Records return (value, key), so for the above example:

  ok     # => ok:
  next   # => 1
  values # => ['1', 0] (values collects the tuple into a list)

The next value is a key which the user can pass to seq\next: to receive the next iteration in the sequence.

This is what makes the sequence lazy - the user computes the next value only when they need it.

  (ok next values*) = ['1' '2' '3' '4'].seq\next 1

  ok     # => ok: 
  next   # => 2
  values # => ['2', 1]

seq\init

seqable.seq\init: () => (next (status ok:, key unknown, values *unknown) | done none:)

Return the initial key and value which should begin the sequence.

seq\next

seqable.seq\init: key unknown => (next (status ok:, key unknown, values *unknown) | done none:)

Given a key, return the next keys and values which would continue the sequence.