LE/1
Langage External. ["An Evaluation of the LE/1 Network Command Language Designed for the SOC Network", J. du Masle, in Command Languages, C. Unger ed, N-H 1973].Last updated: 1994-12-01
leading
<text>
/ledding/ The spacing between lines of text. This is defined when a font is designed but can often be altered in order to change the appearance of the text or for special effects. It is measured in points and is normally 120% of the height of the text.
See also kerning, tracking.Last updated: 1996-06-07
LEAF
<language>
1. LISP Extended Algebraic Facility.
2. "LEAF: A Language which Integrates Logic, Equations and Functions", R. Barbuti et al in Logic Programming, Functions Relations and Equations, D. DeGroot et al eds, P-H 1986, pp.201-238.leaf
<mathematics, data>
(Or "terminal node") In a tree, a node which has no daughter.
Last updated: 1998-11-14
Leaf Distribution Limited
A UK connectivity software supplier which also provides SERVELAN, a country-wide Internet access service. E-mail: <[email protected]>. Address: 7 Elmwood, Chineham Business Park, Crockford Lane, BASINGSTOKE RG24 0WG. Telephone: +44 (1256) 707 777. Fax: +44 (1256) 707 555.Last updated: 1995-01-04
leaf site
A machine that merely originates and reads Usenet news or mail, and does not relay any third-party traffic. Often uttered in a critical tone; when the ratio of leaf sites to backbone, rib, and other relay sites gets too high, the network tends to develop bottlenecks. Compare backbone site, rib site. [Jargon File]League for Programming Freedom
(LPF) A grass-roots organisation of professors, students, businessmen, programmers and users dedicated to bringing back the freedom to write programs. Once programmers were allowed to write programs using all the techniques they knew, and providing whatever features they felt were useful. Monopolies, software patents and interface copyrights have taken away freedom of expression and the ability to do a good job.
"Look and feel" lawsuits attempt to monopolise well-known command languages; some have succeeded. Copyrights on command languages enforce gratuitous incompatibility, close opportunities for competition and stifle incremental improvements. Software patents are even more dangerous; they make every design decision in the development of a program carry a risk of a lawsuit, with draconian pre-trial seizure. It is difficult and expensive to find out whether the techniques you consider using are patented; it is impossible to find out whether they will be patented in the future. The League is not opposed to the legal system that Congress intended -- copyright on individual programs. They aim to reverse the changes made by judges in response to special interests, often explicitly rejecting the public interest principles of the Constitution. The League works to abolish the monopolies by publishing articles, talking with public officials, boycotting egregious offenders and in the future may intervene in court cases. On 1989-05-24, the League picketed Lotus headquarters on account of their lawsuits, and then again on 1990-08-02. These marches stimulated widespread media coverage for the issue. The League's funds are used for filing briefs; printing handouts, buttons and signs and whatever will persuade the courts, the legislators and the people. The League is a non-profit corporation, but not considered a tax-exempt charity. LPF Home.Last updated: 2007-02-28
leak
With a qualifier, one of a class of resource-management bugs that occur when resources are not freed properly after operations on them are finished, so they effectively disappear (leak out). This leads to eventual exhaustion as new allocation requests come in.
One might refer to, say, a "window handle leak" in a window system. See memory leak, fd leak. [Jargon File]Last updated: 1995-04-18
leaky heap
memory leakLean
An experimental language from the University of Nijmegen and University of East Anglia, based on graph rewriting and useful as an intermediate language. Lean is descended from Dactl0. Clean is a subset of Lean. ["Towards an Intermediate Language Based on Graph Rewriting", H.P. Barendregt et al in PARLE: Parallel Architectures and Languages Europe, G. Goos ed, LNCS 259, Springer 1987, pp.159-175].Last updated: 1995-01-25
LEAP
Language for the Expression of Associative Procedures. ALGOL-based formalism for sets and associative retrieval, for TX-2. Became part of SAIL. "An ALGOL-based Associative Language", J.A. Feldman et al, CACM 12(8):439-449 (Aug 1969).leapfrog attack
Use of userid and password information obtained illicitly from one host (e.g. downloading a file of account IDs and passwords, tapping TELNET, etc.) to compromise another host. Also, the act of TELNETting through one or more hosts in order to confuse a trace (a standard cracker procedure). [Jargon File]leap second
Coordinated Universal Timelearning curve
<jargon>
A graph showing some measure of the cost of performing some action against the number of times it has been performed. The term probably entered engineering via the aircraft industry in the 1930s, where it was used to describe plots showing the cost of making some particular design of aeroplane against the number of units made.
The term is also used in psychology to mean a graph showing some measure of something learned against the number of trials. The psychology graphs normally slope upward whereas the manufacturing ones normally slope downward but they are both usually steep to start with and then level out. Marketroids often misuse the term to mean the amount of time it takes to learn to use something ("reduce the learning curve") or the ease of learning it ("easy learning curve"). The phrase "steep learning curve" is sometimes used incorrectly to mean "hard to learn" whereas of course it implies rapid learning. Engineering. Psychology.Last updated: 2002-01-22
leased line
A private telephone circuit permanently connecting two points, normally provided on a lease by a local PTT.
Last updated: 1998-03-24
least fixed point
A function f may have many fixed points (x such that f x = x). For example, any value is a fixed point of the identity function, (\ x . x).
If f is recursive, we can represent it asf = fix Fwhere F is some higher-order function and
fix F = F (fix F).The standard denotational semantics of f is then given by the least fixed point of F. This is the least upper bound of the infinite sequence (the ascending Kleene chain) obtained by repeatedly applying F to the totally undefined value, bottom. I.e.
fix F = LUB {bottom, F bottom, F (F bottom), ...}.The least fixed point is guaranteed to exist for a continuous function over a cpo.
Last updated: 2005-04-12
least recently used
(operating systems) (LRU) A rule used in a paging system which selects a page to be paged out if it has been used (read or written) less recently than any other page. The same rule may also be used in a cache to select which cache entry to flush. This rule is based on temporal locality - the observation that, in general, the page (or cache entry) which has not been accessed for longest is least likely to be accessed in the near future.Last updated: 1995-02-15
least significant bit
<data>
(LSB) Bit zero, the bit of a binary number giving the number of ones, the last or rightmost bit when the number is written in the usual way.
Last updated: 1995-07-13
least upper bound
<theory>
(lub or "join", "supremum") The least upper bound of two elements a and b is an upper bound c such that a <= c and b <= c and if there is any other upper bound c' then c <= c'. The least upper bound of a set S is the smallest b such that for all s in S, s <= b. The lub of mutually comparable elements is their maximum but in the presence of incomparable elements, if the lub exists, it will be some other element greater than all of them.
Lub is the dual to greatest lower bound. (In LaTeX, "<=" is written as \sqsubseteq, the lub of two elements a and b is written a \sqcup b, and the lub of set S is written as \bigsqcup S).Last updated: 1995-02-03
leaves
leafLEC
Local Exchange CarrierLECOM
Version of COMIT on GE 225 ca. 1966. Sammet 1969, p.419.LED
LEDA
Library of Efficient Data types and AlgorithmsLeda
<language>
A multi-paradigm language supporting imperative programming, declarative programming, procedural programming, functional programming, logic programming and object-oriented programming developed by Tim Budd <[email protected]> at Oregon State University in 1990-1993.
["Blending Imperative and Relational Programming", Tim Budd, IEEE Software 8(1):58-65 (Jan 1991)]. Forthcoming book. ftp://cs.orst.edu/pub/budd/leda/.Last updated: 2007-10-02
LED page printer
LED printerLED printer
<printer>
(Or "LED page printer") A printer which is similar in operation to a laser printer, but where an array of LEDs is used in place of the laser.
Last updated: 1996-12-08
leech
Someone who downloads files but provides nothing for others to download. The term is common on BitTorrent, which relies on having multiple sources for files to improve download speed.
Last updated: 2007-03-27
leet
eliteleft arrow
The graphic which the 1963 version of ASCII had in place of the underscore character, ASCII 95.
Last updated: 1995-03-06
left brace
"". {ASCII character 123.
Common names: open brace; left brace; left squiggly; left squiggly bracket/brace; left curly bracket/brace; ITU-T: opening brace. Rare: brace ("}" = unbrace); curly ("}" = uncurly); leftit ("}" = rytit); left squirrelly; INTERCAL: embrace ("}" = bracelet). Paired with right brace ("}").Last updated: 1995-03-16
left bracket
"[". ASCII character 91.
Common: left square bracket; ITU-T: opening bracket; bracket. Rare: square; INTERCAL: U turn. Paired with right bracket ("]").Last updated: 1995-03-16
left join
outer joinleft outer join
outer joinleft parenthesis
"(". ASCII character 40.
Common names: left paren; left parenthesis; left; open; paren (")" = thesis); open paren; open parenthesis; left parenthesis; left banana. Rare: so (")" = already); lparen; ITU-T: opening parenthesis; open round bracket, left round bracket, INTERCAL: wax (")" = wane); parenthisey (")" = unparenthisey); left ear. Paired with right parenthesis (")").Last updated: 1995-03-06
LeFun
Logic, Equations and Functions. An integration of logic programming and functional programming by H. Ait-Kaci et al of MCC, Austin TX. ["LeFun: Logic, Equations and Functions", H. Ait-Kaci et al, Proc 1987 Symp on Logic Programming, San Francisco].Last updated: 1994-10-21
legacy
legacy systemlegacy code
legacy systemlegacy software
legacy systemlegacy system
<jargon>
A computer system or application program which continues to be used because of the cost of replacing or redesigning it and often despite its poor competitiveness and compatibility with modern equivalents. The implication is that the system is large, monolithic and difficult to modify.
If legacy software only runs on antiquated hardware the cost of maintaining this may eventually outweigh the cost of replacing both the software and hardware unless some form of emulation or backward compatibility allows the software to run on new hardware.Last updated: 1998-08-09
legal
Loosely used to mean "in accordance with all the relevant rules", especially in connection with some set of constraints defined by software. "The older =+ alternate for += is no longer legal syntax in ANSI C." "This parser processes each line of legal input the moment it sees the trailing linefeed." Hackers often model their work as a sort of game played with the environment in which the objective is to maneuver through the thicket of "natural laws" to achieve a desired objective. Their use of "legal" is flavoured as much by this game-playing sense as by the more conventional one having to do with courts and lawyers. Compare language lawyer, legalese. [Jargon File]legalese
Dense, pedantic verbiage in a language description, product specification, or interface standard; text that seems designed to obfuscate and requires a language lawyer to parse it. Though hackers are not afraid of high information density and complexity in language (indeed, they rather enjoy both), they share a deep and abiding loathing for legalese; they associate it with deception, suits, and situations in which hackers generally get the short end of the stick.LEGOL
"Application of MP/3 to the Design and Implementation of LEGOL, A Legally Oriented Language", S.H. Mandil et al, Intl Symp Programming, Paris 1974.Le-Lisp
Jerome Chailloux and Emmanuel St James, INRIA, France. A LISP dialect close to Common Lisp, lexically scoped, with a CLOS-like object system. Uses both packages and modules. "le-lisp: A Portable and Efficient Lisp System", J. Chailloux et al, Proc 1984 ACM Symp on Lisp and Functional Programming, ACM. Version v.16, available from ILOG, France.lemma
<logic>
A result already proved, which is needed in the proof of some further result.
Last updated: 1995-03-25
Lempel-Ziv compression
Substitutional compression schemes proposed by Jakob Ziv and Abraham Lempel in 1977 and 1978. There are two main schemes, LZ77 and LZ78. Lempel-Ziv Welch compression is a variant of LZ78.Lempel-Ziv Welch compression
(LZW) The algorithm used by the Unix compress command to reduce the size of files, e.g. for archival or transmission. LZW was designed by Terry Welch in 1984 for implementation in hardware for high-performance disk controllers. It is a variant of LZ78, one of the two Lempel-Ziv compression schemes. The LZW algorithm relies on reoccurrence of byte sequences (strings) in its input. It maintains a table mapping input strings to their associated output codes. The table initially contains mappings for all possible strings of length one. Input is taken one byte at a time to find the longest initial string present in the table. The code for that string is output and then the string is extended with one more input byte, b. A new entry is added to the table mapping the extended string to the next unused code (obtained by incrementing a counter). The process repeats, starting from byte b. The number of bits in an output code, and hence the maximum number of entries in the table is usually fixed and once this limit is reached, no more entries are added. LZW compression and decompression are licensed under Unisys Corporation's 1984 U.S. Patent 4,558,302 and equivalent foreign patents. This kind of patent isn't legal in most coutries of the world (including the UK) except the USA. Patents in the UK can't describe algorithms or mathematical methods. [A Technique for High Performance Data Compression, Terry A. Welch, IEEE Computer, 17(6), June 1984, pp. 8-19] [J. Ziv and A. Lempel, "A Universal Algorithm for Sequential Data Compression," IEEE Transactions on Information Theory, Vol. IT-23, No. 3, May 1977, pp. 337-343].Lenat, Doug
Doug Lenatlenient evaluation
An evaluation strategy, described in [Traub, FPCA 89], under which all redexes are evaluated in parallel except inside the arms of conditionals and inside lambda abstractions. Lenient evaluation is an example of an eager evaluation strategy.
Last updated: 2004-01-22
LEO
Low Earth OrbitLeo
<language>
1. A general-purpose systems language, syntactically like Pascal and Y, semantically like C.
["The Leo Programming Language", G. Townsend, CS TR 84-7, U Arizona 1984].Last updated: 1996-02-06
2. A general data management environment which can show user-created relationships among any kind data. It can also be used as an outlining editor as it embeds the noweb and CWEB markup languages in an outline context.
Leo is written in pure Python using Tk/tcl and so runs on Windows, Linux and MacOS X. It isdistributed under the Python License.Last updated: 2006-07-12
LER
[Jargon File]Last updated: 1999-06-30
LERP
/lerp/ vi., Quasi-acronym for Linear Interpolation, used as a verb or noun for the operation. "Bresenham's algorithm lerps incrementally between the two endpoints of the line." [Jargon File]less than
"<" ASCII character 60.
Common names: ITU-T: less than; bra (">" = ket); left angle; left angle bracket; left broket. Rare: from; read from; suck (">" = blow); comes-from; in; crunch (all from Unix); INTERCAL: angle. See also greater than.Last updated: 1995-03-20
LessTif
<library>
The Hungry Programmers' version of OSF/Motif. It will be source code compatible with Motif, meaning that the same source will compile with both libraries and work exactly the same. All the programming is being done with no reference to the header files for the motif widgets, so that LessTif can be distributed as free software.
http://hungry.com/products/lesstif.Last updated: 1995-03-20
let floating
A program transformation used in functional programming to implement full laziness. E.g. the function
f x = x + sqrt 4can be expressed as
f x = let t = sqrt 4 in x + tbut note that t does not depend on the argument x so we can automatically transform this to
t = sqrt 4 f x = x + tMaking t into a global constant which need only be evaluated at most once, rather than every time f is called. The general idea is to float each subexpression as far out (toward the top level) as possible to maximise sharing.
Last updated: 1997-07-09
letterbomb
1. An e-mail message containing live data intended to do nefarious things to the recipient's computer or terminal. It is possible, for example, to send letterbombs that will lock up some specific kinds of terminals when they are viewed, so thoroughly that the user must turn the terminal off to unwedge it. Under Unix, a letterbomb can also try to get part of its contents interpreted as a shell command. The results of this could range from silly to tragic.
See also Trojan horse; compare nastygram, talk bomb. 2. Loosely, a mailbomb. [Jargon File]Last updated: 1998-01-16
level 1 cache
primary cachelevel 2 cache
secondary cacheLEVEL5 OBJECT
From Information Builders. [What is it?]level one cache
primary cachelevel-sensitive scan design
(circuit design) (LSSD) A kind of scan design which uses separate system and scan clocks to distinguish between normal and test mode. Latches are used in pairs, each has a normal data input, data output and clock for system operation. For test operation, the two latches form a master/slave pair with one scan input, one scan output and non-overlapping scan clocks A and B which are held low during system operation but cause the scan data to be latched when pulsed high during scan.____ | | Sin ----|S | A ------|> | | Q|---+--------------- Q1 D1 -----|D | | CLK1 ---|> | | |__| | __ | | | +---|S | B -------------------|> | | Q|------ Q2 / SOut D2 ------------------|D | CLK2 ----------------|> | |____|In a single latch LSSD configuration, the second latch is used only for scan operation. Allowing it to be use as a second system latch reduces the silicon overhead.
Last updated: 1995-02-15
level two cache
secondary cacheLex
<tool>
1. A lexical analyser generator for Unix and its input language. There is a GNU version called flex and a version written in, and outputting, SML/NJ called ML-lex. A version, by David Poole at Montana has been retargeted to Turbo Pascal, ftp://iecc.com/pub/file/lyprg.zip.
["Lex - A Lexical Analyzer Generator", M.E. Lesk, CS TR 39, Bell Labs, Oct 1975].2. The lexical specification language for COPS.
["Metalanguages of the Compiler Production System COPS", J. Borowiec, in GI Fachgesprach "Compiler-Compiler", ed W. Henhapl, Tech Hochs Darmstadt 1978, pp.122-159].Last updated: 2000-11-15
lexeme
<grammar>
A minimal lexical unit of a language. Lexical analysis converts strings in a language into a list of lexemes. For a programming language these word-like pieces would include keywords, identifiers, literals and punctuation. The lexemes are then passed to the parser for syntactic analysis.
Last updated: 1996-04-06
lexer
lexical analyserlexical analyser
<language>
(Or "scanner") The initial input stage of a language processor (e.g. a compiler), the part that performs lexical analysis.
Last updated: 1995-04-05
lexical analysis
(Or "linear analysis", "scanning") The first stage of processing a language. The stream of characters making up the source program or other input is read one at a time and grouped into lexemes (or "tokens") - word-like pieces such as keywords, identifiers, literals and punctuation. The lexemes are then passed to the parser.
["Compilers - Principles, Techniques and Tools", by Alfred V. Aho, Ravi Sethi and Jeffrey D. Ullman, pp. 4-5]Last updated: 1995-04-05
lexical scope
(Or "static scope") When the scope of an identifier is fixed at compile time to some region in the source code containing the identifier's declaration. This means that an identifier is only accessible within that region (including procedures declared within it).
This contrasts with dynamic scope where the scope depends on the nesting of procedure and function calls at run time. Statically scoped languages differ as to whether the scope is limited to the smallest block (including begin/end blocks) containing the identifier's declaration (e.g. C, Perl) or to whole function and procedure bodies (e.g. ECMAScript), or some larger unit of code (e.g. ?). The former is known as static nested scope.Last updated: 2005-07-28
lexical scoping
lexical scopelexiphage
<graphics>
/lek'si-fayj"/ A notorious word chomper, implemented and named by John Doty in late 1972 on and HP calculator and later on ITS. The lexiphage program would draw on a selected victim's bitmapped terminal the words "THE BAG" in ornate letters, followed a pair of jaws biting pieces of it off.
http://lexiphage.com/). [Jargon File]Last updated: 2002-06-12
Nearby terms:
LDL1 ♦ LDP ♦ LDT ♦ LE/1 ♦ leading ♦ LEAF ♦ leaf ♦ Leaf Distribution Limited
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