nonempty.scp (295B)
1 !export nonempty 2 -- Test whether a list has a head; its elements are not inspected. 3 -- Input: a list; state: ignored. Returns tree Booleans: leaf for [], 4 -- stem leaf for any nonempty list. Useful as the predicate for filter. 5 consumer nonempty 6 [] @ _ => leaf 7 [x | xs] @ _ => stem leaf