Head Disk Assembly definition
<hardware, storage> (HDA) A sealed, high capacity mainframe
hard disk with integral heads, as opposed to a removable
disk.
(1999-01-13)
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HDSL « HDTV « hdx « Head Disk Assembly » header » Head Normal Form » head normalisation theorem
header definition
1. The portion of a packet, preceding the actual data,
containing source and destination addresses, error checking
and other fields.
2. The part of an electronic mail message or news article
that precedes the body of a message and contains, among other
things, the sender's name and e-mail address and the date and
time the message was sent.
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HDTV « hdx « Head Disk Assembly « header » Head Normal Form » head normalisation theorem » heads down
Head Normal Form definition
<theory, reduction> (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)
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head normalisation theorem definition
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.
Nearby terms:
Head Disk Assembly « header « Head Normal Form « head normalisation theorem » heads down » head-strict » heap
heads down definition
[Sun] Concentrating, usually so heavily and for so long that
everything outside the focus area is missed. See also hack
mode and larval stage, although this mode is hardly
confined to fledgling hackers.
[Jargon File]
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header « Head Normal Form « head normalisation theorem « heads down » head-strict » heap » heartbeat
head-strict definition
<theory> A head-strict function will not necessarily evaluate
every cons cell of its (list) argument, but whenever it does
evaluate a cons cell it will also evaluate the element in the
head of that cell. An example of a head-strict function is
beforeZero :: [Int] -> [Int]
beforeZero [] = []
beforeZero (0:xs) = []
beforeZero (x:xs) = x : beforeZero xs
which returns a list up to the first zero.
This pattern of evaluation is important because it is common
in functions which operate on a list of inputs.
See also tail-strict, hyperstrict.
(1995-05-11)
Nearby terms:
Head Normal Form « head normalisation theorem « heads down « head-strict » heap » heartbeat » heatseeker
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