sentinels

Module nu.lang.sentinels.

Sentinels - EMPTY and UNSET.

EMPTY is the one "no value" sentinel: no value here, either missing or derived from missing. It originates at Ref resolution (the address resolves to nothing) and flows from there like NULL in SQL: unknown flows through expressions and never passes a condition.

• Queries propagate it. Any EMPTY operand gives EMPTY, without raising.
• Conditions read it as false. A branch, loop, filter or And / Or treats EMPTY like any falsy value, without poisoning the rest.
• Writes refuse it. Storing EMPTY into a Ref or fabric raises; absence is made by erasing, never by writing.
• Real errors stay errors. A wrong type or a bad call raises as in Python.

The checks that observe EMPTY (IsEmpty, exists(), fallback()) take it as an ordinary input and yield a real answer. In a Stream, EMPTY is just one yielded value; the stream consumer decides what it means per element.

is_empty

True if value is the EMPTY sentinel.

lang.is_empty(value)

Path nu.lang.is_empty. Defined on nu.lang.sentinels, bound as a function. Builds TypeGuard[Empty].

Arguments

Undocumented: example.

is_sentinel

True if value is any Sentinel.

lang.is_sentinel(value)

Path nu.lang.is_sentinel. Defined on nu.lang.sentinels, bound as a function. Builds TypeGuard[Sentinel].

Arguments

Undocumented: example.