(HNF) A term describing a lambda expression whose top level is either a variable, a data value, a built-in function applied to too few arguments, or a lambda abstraction whose body is not reducible. I.e. the top level is neither a redex nor a lambda abstraction with a reducible body.
An expression in HNF may contain redexes in argument postions whereas a normal form may not.
Compare Weak Head Normal Form.
- Head normalisation theorem
Under the typed lambda-calculus, beta/delta reduction of the left-most redex (normal order reduction) is guaranteed to terminate with a head normal form if one exists. See also Church-Rosser theorem.
[hed-noht] /ˈhɛdˌnoʊt/ noun 1. a brief summary, comment, or explanation that precedes a chapter, report, etc.
- Head of all the heads
noun phrase The highest-ranking chief; the big chief; capo di tutti capi: Head of all the heads, you understand my meaning? (1970s+) Related Terms capo
- Head off at the pass
verb phrase To forestall or prevent by anticipation: A single mother has to establish control fast, before the coercive cycle builds. You have to head it off at the pass [1930s+; fr the stock situation in western movies, where typically the leader of a force pursuing thieves or rustlers through rough ground declares, ”We’ll head […]