error yield-outside-stream

`yield` допустим только в функции с результатом `stream<T, E>`.

What it means#

A generator is a function whose result type is stream<T, E> and whose body contains yield (§10.3). yield x hands the element x (a T) to the consumer of the stream and suspends the body until the consumer asks for the next one. Anywhere else — in an ordinary function, in a lambda inside a generator (a lambda is a different function), or in a function whose result is not a stream — there is no stream to yield to.

Example#

fn plain() -> i32 {
  yield 1       // <- yield-outside-stream
  2
}

yield-outside-stream

How to fix#

Declare the function as a generator, or return the value:

fn numbers() -> stream<i32> {
  yield 1
  yield 2
}

See also#

• type-mismatch
• fail-type