Attempt

A call that can fail must say so where it is called. attempt passes the call's failures on to the caller, whose fails list must include them. A match on the call handles them instead.

attempt starts a statement: a variable, a return, or a statement on its own.

var todo: Todo = attempt Todo.get(todo_id)return attempt todo_by_id(todo_id)attempt Todo.get(todo_id)

It can't stand inside an expression, so this is refused:

var total: Stock = Stock(attempt stock_of(a) + attempt stock_of(b))

So every point where a callable can stop early is at the start of a line. attempt on a call that can't fail is an error.

reject and propagate follow the same rule: each starts a statement or is the result of a match arm, never part of a value (failure.reject_placement, failure.propagate_placement). More is in Passing a failure on: attempt.