(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. (2003-01-08)
