Computer Music Journal Conference Proceedings IEEE and IRE Miscellaneous Word Processing, Data Processing Item Details. Winston, Patrick Henry; Berthold Klaus Paul Horn. Addison-Wesley Boston MA 1981, 430 pages. Condition: Very Good overall, glossy cover softcover, some.
- Lisp.pdf - Free download Ebook, Handbook, Textbook, User Guide PDF files on the internet quickly and easily.
- CS A331 Programming Language Concepts. Lecture 10 – Alternative Programming Languages (Functional – LISP. Lisp Basics – Winston & Horn Sam Siewert 3 (setf friends '(dick jane sally)). Common Lisp Though is Portable, Comprehensive and Lots.
My colleagues were using C (K&R in those days) or Pascal. C, Perl,Java, Python, etc. Didn't exist. When all those modern languages areout of the picture, Lisp rocks.I've used Java and Python professionally for years and I can firmly say Lisp rocks compared to them. No experience with perl, though.Once upona time Lisp had a long list of features that no other language had (GC,full numeric tower, CLOS, incremental development, macros)Well, it's 2018 and almost no OOP language has the power, features and flexibility of Lisp's CLOS, except for Dylan,and Julia.It's 2018 and the kind of fully flexible interactive development where the running system can be updated at will (i.e.
Redefine/recompile a function or redefine a. Class while the code is running) and it is also image-based, is AFAIK still only available in Lisp and Smalltalk. This gives enormous productivity.In fact, in his web page, Ron Garret aka Erran Gat (the OP) illustrates how this feature was crucial for NASA's Deep Space 1 project:In 1994 JPL started working on the Remote Agent (RA), an autonomous spacecraft control system. RA was written entirely in Common Lisp despite unrelenting political pressure to move to C. At one point an attempt was made to port one part of the system (the planner) to C.
This attempt had to be abandoned after a year. Based on this experience I think it's safe to say that if not for Lisp the Remote Agent would have failed.(.)The Remote Agent software, running on a custom port of Harlequin Common Lisp, flew aboard Deep Space 1 (DS1), the first mission of NASA's New Millennium program. Remote Agent controlled DS1 for two days in May of 1999. During that time we were able to debug and fix a race condition that had not shown up during ground testing. (Debugging a program running on a $100M piece of hardware that is 100 million miles away is an interesting experience.
Having a read-eval-print loop running on the spacecraft proved invaluable in finding and fixing the problem. The story of the Remote Agent bug is an interesting one in and of itself.)The Remote Agent was subsequently named 'NASA Software of the Year'. That’s a strategic benefit only if high reliability through dynamic code reloading becomes a more significant factor in software systems demanded by customers. At the moment, Linux hasn’t eliminated reboots on security updates yet, even though.
There is apparently a lot of high reliability and high serviceability mechanisms and techniques in the mainframe world that we in the distributed world haven’t picked up yet, from my casual look into it. My guess is there isn’t a large enough demand for those far rightward nines to make it a market priority at the time, and what we have is good enough for now.The best that non-Lisp&Smalltalk languages can deliver at the moment. They require either accommodations in design (Erlang hot code loading), or implementation/operation (Ruby monkey patching).
Not as seamless as a SLIME-integrated environment, though I don’t know the limits to Lisp’s hot code updating. But until the market demands it, I’m not sure it is compelling enough of an advantage in general cases. Interestingly, when I learnt Python i was surprised at how legible my code could become, for example by using named parameters. I was glad that CL supported named parameters as well (by using keywords).I write a very lisp-ified dialect of Python using things like,which mimic their namesakes in CLOS. I use defmethod along with the python-inferior-shell (tied to iPython) to iterate very quickly on 'things'. This has the concomitant effect of making my code quite dense, because all the scratch-work that went into 'deriving' it is gone. Ditto with SLIME and CL.Sadly, Python's module support is supremely woeful, so I can't switch and change things in a library - this is extremely frustrating.
Thank you for sharing! I'm a devoted Lisper, and now that you brought it up, I can begin to see this complacency creeping in to my attitude about programming.Question for you: the productivity gains (or even straight-up advantages over Lisp) that you noticed - do you think that perhaps they could have been partially or mostly caused by the massive library advantage that other languages have over Lisp?
For instance, as someone who's written a non-trivial amount of Python code over the past few years, I can confirm that, while it's much less powerful and expressive than CL, it has libraries for everything.
ANSI-standardized dialect of Lisp Common Lisp:,Family,ANSI committeeFirst appeared1984 (35 years ago) ( 1984), 1994 (25 years ago) ( 1994) for ANSI Common Lisp,lexical, optionally dynamic.lisp,.lsp,.l,.cl,.faslWebsiteMajor,CLtL1, CLtL2, ANSI Common LispInfluenced by,Influenced,Common Lisp ( CL) is a dialect of the, published in standard document ANSI INCITS 226-1994 (R2004) (formerly X3.226-1994 (R1999)). The, a hyperlinked HTML version, has been derived from the ANSI Common Lisp standard.The Common Lisp language was developed as a standardized and improved successor of. By the early 1980s several groups were already at work on diverse successors to MacLisp: (aka ZetaLisp),. Common Lisp sought to unify, standardise, and extend the features of these MacLisp dialects.
Common Lisp is not an implementation, but rather a language. Several of the Common Lisp standard are available, including and proprietary products.Common Lisp is a general-purpose,. It supports a combination of, and paradigms. As a, it facilitates evolutionary and, with iterative into efficient run-time programs. This incremental development is often done interactively without interrupting the running application.It also supports optional type annotation and casting, which can be added as necessary at the later and optimization stages, to permit the compiler to generate more efficient code. For instance, fixnum can hold an integer in a range supported by the hardware and implementation, permitting more efficient arithmetic than on big integers or arbitrary precision types. Similarly, the compiler can be told on a per-module or per-function basis which type safety level is wanted, using optimize declarations.Common Lisp includes, an that supports and method combinations.
It is often implemented with a Protocol.Common Lisp is extensible through standard features such as Lisp (code transformations) and reader macros (input parsers for characters).Common Lisp provides some backwards compatibility to and to John McCarthy's original. This allows older Lisp software to be ported to Common Lisp. Contents.History Work on Common Lisp started in 1981 after an initiative by ARPA manager Bob Engelmore to develop a single community standard Lisp dialect. Much of the initial language design was done via electronic mail. In 1982, gave the first overview of Common Lisp at the 1982 ACM Symposium on LISP and functional programming.The first language documentation was published 1984 as, first edition. A second edition, published in 1990, incorporated many changes to the language, made during the ANSI Common Lisp standardization process.
The final ANSI Common Lisp standard then was published in 1994. Since then no update to the standard has been published.
Various extensions and improvements to Common Lisp (examples are Unicode, Concurrency, CLOS-based IO) have been provided by implementations and libraries (many available via ).Timeline of Lisp dialects 152019LISP 1, 1.5,R5RSR6RSR7RS smallQi, QiIIShenSyntax Common Lisp is a dialect of Lisp. It uses to denote both code and data structure. Function calls, macro forms and special forms are written as lists, with the name of the operator first, as in these examples. The 'let' construct creates a scope for local variables.
Here;; the variable 'a' is bound to 6 and the variable 'b' is bound;; to 4. Inside the 'let' is a 'body', where the last computed value is returned.;; Here the result of adding a and b is returned from the 'let' expression.;; The variables a and b have lexical scope, unless the symbols have been;; marked as special variables (for instance by a prior DEFVAR). ( let (( a 6 ) ( b 4 )) ( + a b )); returns 10 Data types Common Lisp has many.Scalar types Number types include,. Common Lisp uses to represent numerical values of arbitrary size and precision.
The ratio type represents fractions exactly, a facility not available in many languages. Common Lisp automatically coerces numeric values among these types as appropriate.The Common Lisp type is not limited to characters. Most modern implementations allow characters.The type is common to Lisp languages, but largely unknown outside them.
A symbol is a unique, named data object with several parts: name, value, function, property list and package. Of these, value cell and function cell are the most important.
Symbols in Lisp are often used similarly to identifiers in other languages: to hold the value of a variable; however there are many other uses. Normally, when a symbol is evaluated, its value is returned. Some symbols evaluate to themselves, for example all symbols in the keyword package are self-evaluating. Boolean values in Common Lisp are represented by the self-evaluating symbols T and NIL.
Common Lisp has namespaces for symbols, called 'packages'.A number of functions are available for scalar numeric values in various ways. The function round rounds the argument to the nearest integer, with halfway cases rounded to the even integer. The functions truncate, floor, and ceiling round towards zero, down, or up respectively.
All these functions return the discarded fractional part as a secondary value. For example, (floor -2.5) yields -3, 0.5; (ceiling -2.5) yields -2, -0.5; (round 2.5) yields 2, 0.5; and (round 3.5) yields 4, -0.5.Data structures Sequence types in Common Lisp include lists, vectors, bit-vectors, and strings.
There are many operations that can work on any sequence type.As in almost all other Lisp dialects, lists in Common Lisp are composed of conses, sometimes called cons cells or pairs. A cons is a data structure with two slots, called its car and cdr. A list is a linked chain of conses or the empty list. Each cons's car refers to a member of the list (possibly another list).
Each cons's cdr refers to the next cons—except for the last cons in a list, whose cdr refers to the nil value. Conses can also easily be used to implement trees and other complex data structures; though it is usually advised to use structure or class instances instead. It is also possible to create circular data structures with conses.Common Lisp supports multidimensional arrays, and can dynamically resize adjustable arrays if required. Multidimensional arrays can be used for matrix mathematics.
A vector is a one-dimensional array. Arrays can carry any type as members (even mixed types in the same array) or can be specialized to contain a specific type of members, as in a vector of bits. Usually only a few types are supported. Many implementations can optimize array functions when the array used is type-specialized. Two type-specialized array types are standard: a string is a vector of characters, while a bit-vector is a vector of.store associations between data objects. Any object may be used as key or value. Hash tables are automatically resized as needed.Packages are collections of symbols, used chiefly to separate the parts of a program into.
A package may export some symbols, marking them as part of a public interface. Packages can use other packages.Structures, similar in use to structs and records, represent arbitrary complex data structures with any number and type of fields (called slots).
Structures allow single-inheritance.Classes are similar to structures, but offer more dynamic features and multiple-inheritance. Classes have been added late to Common Lisp and there is some conceptual overlap with structures. Objects created of classes are called Instances. A special case are Generic Functions. Generic Functions are both functions and instances.Functions Common Lisp supports. For instance, it is possible to write functions that take other functions as arguments or return functions as well.
This makes it possible to describe very general operations.The Common Lisp library relies heavily on such higher-order functions. For example, the sort function takes a as an argument and key function as an optional keyword argument. This can be used not only to sort any type of data, but also to sort data structures according to a key. Sorts the list according to the first element of each sub-list. ( sort ( list ' ( 9 A ) ' ( 3 B ) ' ( 4 C )) #'. ( flet (( square ( x ) (. x x ))) ( square 3 ))There are a number of other operators related to the definition and manipulation of functions.
For instance, a function may be compiled with the compile operator. (Some Lisp systems run functions using an interpreter by default unless instructed to compile; others compile every function).Defining generic functions and methods The macro defgeneric defines. Generic functions are a collection of.The macro defmethod defines methods.Methods can specialize their parameters over CLOS standard classes, system classes, structure classes or individual objects. For many types there are corresponding system classes.When a generic function is called, will determine the effective method to use. ( add 2 3 ); returns 5 ( add #( 1 2 3 4 ) 7 ); returns #(8 9 10 11) ( add #( 1 2 3 4 ) #( 4 3 2 1 )); returns #(5 5 5 5) ( add 'COMMON ' 'LISP' ); returns 'COMMON LISP'Generic Functions are also a. There are many more features to Generic Functions and Methods than described above.The function namespace The namespace for function names is separate from the namespace for data variables.
This is a key difference between Common Lisp. For Common Lisp, operators that define names in the function namespace include defun, flet, labels, defmethod and defgeneric.To pass a function by name as an argument to another function, one must use the function special operator, commonly abbreviated as #'. The first sort example above refers to the function named by the symbol in the function namespace, with the code #'. Conversely, to call a function passed in such a way, one would use the funcall operator on the argument.evaluation model is simpler: there is only one namespace, and all positions in the form are evaluated (in any order) - not just the arguments. Code written in one dialect is therefore sometimes confusing to programmers more experienced in the other. For instance, many Common Lisp programmers like to use descriptive variable names such as list or string which could cause problems in Scheme, as they would locally shadow function names.Whether a separate namespace for functions is an advantage is a source of contention in the Lisp community.
It is usually referred to as the Lisp-1 vs. Lisp-2 debate. Lisp-1 refers to Scheme's model and Lisp-2 refers to Common Lisp's model. These names were coined in a 1988 paper by and, which extensively compares the two approaches. Multiple return values Common Lisp supports the concept of multiple values, where any expression always has a single primary value, but it might also have any number of secondary values, which might be received and inspected by interested callers. This concept is distinct from returning a list value, as the secondary values are fully optional, and passed via a dedicated side channel. This means that callers may remain entirely unaware of the secondary values being there if they have no need for them, and it makes it convenient to use the mechanism for communicating information that is sometimes useful, but not always necessary.
For example,. The TRUNCATE function rounds the given number to an towards zero. However, it also returns a remainder as a secondary value, making it very easy to determine what value was truncated. It also supports an optional divisor parameter, which can be used to perform trivially. ( let (( x 1266778 ) ( y 458 )) ( multiple-value-bind ( quotient remainder ) ( truncate x y ) ( format nil 'A divided by A is A remainder A' x y quotient remainder )));;;; = '1266778 divided by 458 is 2765 remainder 408'.
GETHASH returns the value of a key in an, or the default value otherwise, and a secondary boolean indicating whether the value was found. Thus code which does not care about whether the value was found or provided as the default can simply use it as-is, but when such distinction is important, it might inspect the secondary boolean and react appropriately. Both use cases are supported by the same call and neither is unnecessarily burdened or constrained by the other. Having this feature at the language level removes the need to check for the existence of the key or compare it to as would be done in other languages. ( defun magic-eight-ball 'Return an outlook prediction, with the probability as a secondary value' ( values 'Outlook good' ( random 1.0 )));;;; = 'Outlook good';;;; = 0.3187 Other types Other data types in Common Lisp include:. Pathnames represent files and directories in the. The Common Lisp pathname facility is more general than most operating systems' file naming conventions, making Lisp programs' access to files broadly portable across diverse systems.
Input and output streams represent sources and sinks of binary or textual data, such as the terminal or open files. Common Lisp has a built-in (PRNG). Random state objects represent reusable sources of pseudo-random numbers, allowing the user to seed the PRNG or cause it to replay a sequence. Conditions are a type used to represent errors, exceptions, and other 'interesting' events to which a program may respond. Classes are, and are themselves instances of classes called ( for short).
Readtables are a type of object which control how Common Lisp's reader parses the text of source code. By controlling which readtable is in use when code is read in, the programmer can change or extend the language's syntax.Scope Like programs in many other programming languages, Common Lisp programs make use of names to refer to variables, functions, and many other kinds of entities.
Named references are subject to scope.The association between a name and the entity which the name refers to is called a binding.Scope refers to the set of circumstances in which a name is determined to have a particular binding.Determiners of scope The circumstances which determine scope in Common Lisp include:. the location of a reference within an expression. If it's the leftmost position of a compound, it refers to a special operator or a macro or function binding, otherwise to a variable binding or something else.
the kind of expression in which the reference takes place. For instance, (go x) means transfer control to label x, whereas (print x) refers to the variable x. Both scopes of x can be active in the same region of program text, since tagbody labels are in a separate namespace from variable names. A special form or macro form has complete control over the meanings of all symbols in its syntax. For instance, in (defclass x (a b) ), a class definition, the (a b) is a list of base classes, so these names are looked up in the space of class names, and x isn't a reference to an existing binding, but the name of a new class being derived from a and b. These facts emerge purely from the semantics of defclass.
The only generic fact about this expression is that defclass refers to a macro binding; everything else is up to defclass. the location of the reference within the program text. For instance, if a reference to variable x is enclosed in a binding construct such as a let which defines a binding for x, then the reference is in the scope created by that binding. for a variable reference, whether or not a variable symbol has been, locally or globally, declared special. This determines whether the reference is resolved within a lexical environment, or within a dynamic environment.
the specific instance of the environment in which the reference is resolved. An environment is a run-time dictionary which maps symbols to bindings. Each kind of reference uses its own kind of environment. References to lexical variables are resolved in a lexical environment, et cetera. More than one environment can be associated with the same reference.
For instance, thanks to recursion or the use of multiple threads, multiple activations of the same function can exist at the same time. These activations share the same program text, but each has its own lexical environment instance.To understand what a symbol refers to, the Common Lisp programmer must know what kind of reference is being expressed, what kind of scope it uses if it is a variable reference (dynamic versus lexical scope), and also the run-time situation: in what environment is the reference resolved, where was the binding introduced into the environment, et cetera.Kinds of environment Global Some environments in Lisp are globally pervasive.
For instance, if a new type is defined, it is known everywhere thereafter. References to that type look it up in this global environment.Dynamic One type of environment in Common Lisp is the dynamic environment. Bindings established in this environment have dynamic extent, which means that a binding is established at the start of the execution of some construct, such as a let block, and disappears when that construct finishes executing: its lifetime is tied to the dynamic activation and deactivation of a block. However, a dynamic binding is not just visible within that block; it is also visible to all functions invoked from that block. This type of visibility is known as indefinite scope.
Bindings which exhibit dynamic extent (lifetime tied to the activation and deactivation of a block) and indefinite scope (visible to all functions which are called from that block) are said to have dynamic scope.Common Lisp has support for dynamically scoped variables, which are also called special variables. Certain other kinds of bindings are necessarily dynamically scoped also, such as restarts and catch tags. Function bindings cannot be dynamically scoped using flet (which only provides lexically scoped function bindings), but function objects (a first-level object in Common Lisp) can be assigned to dynamically scoped variables, bound using let in dynamic scope, then called using funcall or APPLY.Dynamic scope is extremely useful because it adds referential clarity and discipline to. Global variables are frowned upon in computer science as potential sources of error, because they can give rise to ad-hoc, covert channels of communication among modules that lead to unwanted, surprising interactions.In Common Lisp, a special variable which has only a top-level binding behaves just like a global variable in other programming languages.
A new value can be stored into it, and that value simply replaces what is in the top-level binding. Careless replacement of the value of a global variable is at the heart of bugs caused by use of global variables. However, another way to work with a special variable is to give it a new, local binding within an expression. This is sometimes referred to as 'rebinding' the variable.
Binding a dynamically scoped variable temporarily creates a new memory location for that variable, and associates the name with that location. While that binding is in effect, all references to that variable refer to the new binding; the previous binding is hidden. When execution of the binding expression terminates, the temporary memory location is gone, and the old binding is revealed, with the original value intact.
Of course, multiple dynamic bindings for the same variable can be nested.In Common Lisp implementations which support multithreading, dynamic scopes are specific to each thread of execution. Thus special variables serve as an abstraction for thread local storage. If one thread rebinds a special variable, this rebinding has no effect on that variable in other threads. The value stored in a binding can only be retrieved by the thread which created that binding. If each thread binds some special variable.x., then.x. behaves like thread-local storage. Among threads which do not rebind.x., it behaves like an ordinary global: all of these threads refer to the same top-level binding of.x.Dynamic variables can be used to extend the execution context with additional context information which is implicitly passed from function to function without having to appear as an extra function parameter.
This is especially useful when the control transfer has to pass through layers of unrelated code, which simply cannot be extended with extra parameters to pass the additional data. A situation like this usually calls for a global variable. That global variable must be saved and restored, so that the scheme doesn't break under recursion: dynamic variable rebinding takes care of this. And that variable must be made thread-local (or else a big mutex must be used) so the scheme doesn't break under threads: dynamic scope implementations can take care of this also.In the Common Lisp library, there are many standard special variables. For instance, all standard I/O streams are stored in the top-level bindings of well-known special variables. The standard output stream is stored in.standard-output.Suppose a function foo writes to standard output. ( with-output-to-string (.standard-output.
) ( foo )) - 'Hello, world'; gathered output returned as a stringLexical Common Lisp supports lexical environments. Formally, the bindings in a lexical environment have and may have either indefinite extent or dynamic extent, depending on the type of namespace.
Means that visibility is physically restricted to the block in which the binding is established. References which are not textually (i.e. Lexically) embedded in that block simply do not see that binding.The tags in a TAGBODY have lexical scope. The expression (GO X) is erroneous if it is not actually embedded in a TAGBODY which contains a label X. However, the label bindings disappear when the TAGBODY terminates its execution, because they have dynamic extent. If that block of code is re-entered by the invocation of a, it is invalid for the body of that closure to try to transfer control to a tag via GO.
( defvar.stashed. );; will hold a function ( tagbody ( setf.stashed.
( lambda ( go some-label ))) ( go end-label );; skip the (print 'Hello') some-label ( print 'Hello' ) end-label ) - NILWhen the TAGBODY is executed, it first evaluates the setf form which stores a function in the special variable.stashed. Then the (go end-label) transfers control to end-label, skipping the code (print 'Hello'). Since end-label is at the end of the tagbody, the tagbody terminates, yielding NIL.
Suppose that the previously remembered function is now called. ( funcall.stashed. );; Error!This situation is erroneous. One implementation's response is an error condition containing the message, 'GO: tagbody for tag SOME-LABEL has already been left'. The function tried to evaluate (go some-label), which is lexically embedded in the tagbody, and resolves to the label. However, the tagbody isn't executing (its extent has ended), and so the control transfer cannot take place.Local function bindings in Lisp have, and variable bindings also have lexical scope by default. By contrast with GO labels, both of these have indefinite extent.
When a lexical function or variable binding is established, that binding continues to exist for as long as references to it are possible, even after the construct which established that binding has terminated. References to lexical variables and functions after the termination of their establishing construct are possible thanks to.Lexical binding is the default binding mode for Common Lisp variables.
For an individual symbol, it can be switched to dynamic scope, either by a local declaration, by a global declaration. The latter may occur implicitly through the use of a construct like DEFVAR or DEFPARAMETER.
It is an important convention in Common Lisp programming that special (i.e. Dynamically scoped) variables have names which begin and end with an asterisk. in what is called the “ convention”. If adhered to, this convention effectively creates a separate namespace for special variables, so that variables intended to be lexical are not accidentally made special.is useful for several reasons.Firstly, references to variables and functions can be compiled to efficient machine code, because the run-time environment structure is relatively simple. In many cases it can be optimized to stack storage, so opening and closing lexical scopes has minimal overhead. ( defmacro until ( test &body body ) ( let (( start-tag ( gensym 'START' )) ( end-tag ( gensym 'END' ))) ` ( tagbody, start-tag ( when, test ( go, end-tag )) ( progn,@ body ) ( go, start-tag ), end-tag )))tagbody is a primitive Common Lisp special operator which provides the ability to name tags and use the go form to jump to those tags. The backquote ` provides a notation that provides code templates, where the value of forms preceded with a comma are filled in.
Forms preceded with comma and at-sign are spliced in. The tagbody form tests the end condition. If the condition is true, it jumps to the end tag. Otherwise the provided body code is executed and then it jumps to the start tag.An example form using above until macro. ( TAGBODY #:START1136 ( WHEN ( ZEROP ( RANDOM 10 )) ( GO #:END1137 )) ( PROGN ( WRITE-LINE 'hello' )) ( GO #:START1136 ) #:END1137 )During macro expansion the value of the variable test is (= (random 10) 0) and the value of the variable body is ((write-line 'Hello')).
The body is a list of forms.Symbols are usually automatically upcased. The expansion uses the TAGBODY with two labels. The symbols for these labels are computed by GENSYM and are not interned in any package. Two go forms use these tags to jump to. Since tagbody is a primitive operator in Common Lisp (and not a macro), it will not be expanded into something else. The expanded form uses the when macro, which also will be expanded. Fully expanding a source form is called code walking.In the fully expanded ( walked) form, the when form is replaced by the primitive if.
( TAGBODY #:START1136 ( IF ( ZEROP ( RANDOM 10 )) ( PROGN ( GO #:END1137 )) NIL ) ( PROGN ( WRITE-LINE 'hello' )) ( GO #:START1136 )) #:END1137 )All macros must be expanded before the source code containing them can be evaluated or compiled normally. Macros can be considered functions that accept and return - similar to, but not limited to those. These functions are invoked before the evaluator or compiler to produce the final source code.Macros are written in normal Common Lisp, and may use any Common Lisp (or third-party) operator available.Variable capture and shadowing Common Lisp macros are capable of what is commonly called variable capture, where symbols in the macro-expansion body coincide with those in the calling context, allowing the programmer to create macros wherein various symbols have special meaning. The term variable capture is somewhat misleading, because all namespaces are vulnerable to unwanted capture, including the operator and function namespace, the tagbody label namespace, catch tag, condition handler and restart namespaces.Variable capture can introduce software defects. This happens in one of the following two ways:.
In the first way, a macro expansion can inadvertently make a symbolic reference which the macro writer assumed will resolve in a global namespace, but the code where the macro is expanded happens to provide a local, shadowing definition which steals that reference. Let this be referred to as type 1 capture. The second way, type 2 capture, is just the opposite: some of the arguments of the macro are pieces of code supplied by the macro caller, and those pieces of code are written such that they make references to surrounding bindings.
However, the macro inserts these pieces of code into an expansion which defines its own bindings that accidentally captures some of these references.The Scheme dialect of Lisp provides a macro-writing system which provides the referential transparency that eliminates both types of capture problem. This type of macro system is sometimes called 'hygienic', in particular by its proponents (who regard macro systems which do not automatically solve this problem as unhygienic). In Common Lisp, macro hygiene is ensured one of two different ways.One approach is to use: guaranteed-unique symbols which can be used in a macro-expansion without threat of capture. The use of gensyms in a macro definition is a manual chore, but macros can be written which simplify the instantiation and use of gensyms. Gensyms solve type 2 capture easily, but they are not applicable to type 1 capture in the same way, because the macro expansion cannot rename the interfering symbols in the surrounding code which capture its references.
Gensyms could be used to provide stable aliases for the global symbols which the macro expansion needs. The macro expansion would use these secret aliases rather than the well-known names, so redefinition of the well-known names would have no ill effect on the macro.Another approach is to use packages. A macro defined in its own package can simply use internal symbols in that package in its expansion. The use of packages deals with type 1 and type 2 capture.However, packages don't solve the type 1 capture of references to standard Common Lisp functions and operators. The reason is that the use of packages to solve capture problems revolves around the use of private symbols (symbols in one package, which are not imported into, or otherwise made visible in other packages).
Whereas the Common Lisp library symbols are external, and frequently imported into or made visible in user-defined packages.The following is an example of unwanted capture in the operator namespace, occurring in the expansion of a macro. Expansion of UNTIL makes liberal use of DO ( defmacro until ( expression &body body ) ` ( do (, expression ),@ body ));; macrolet establishes lexical operator binding for DO ( macrolet (( do (. Something else. )) ( until ( = ( random 10 ) 0 ) ( write-line 'Hello' )))The until macro will expand into a form which calls do which is intended to refer to the standard Common Lisp macro do. However, in this context, do may have a completely different meaning, so until may not work properly.Common Lisp solves the problem of the shadowing of standard operators and functions by forbidding their redefinition.
Because it redefines the standard operator do, the preceding is actually a fragment of non-conforming Common Lisp, which allows implementations to diagnose and reject it.Condition system The condition system is responsible for in Common Lisp. It provides conditions, handlers and restarts. Conditions are objects describing an exceptional situation (for example an error). If a condition is signaled, the Common Lisp system searches for a handler for this condition type and calls the handler.
The handler can now search for restarts and use one of these restarts to automatically repair the current problem, using information such as the condition type and any relevant information provided as part of the condition object, and call the appropriate restart function.These restarts, if unhandled by code, can be presented to users (as part of a user interface, that of a debugger for example), so that the user can select and invoke one of the available restarts. Since the condition handler is called in the context of the error (without unwinding the stack), full error recovery is possible in many cases, where other exception handling systems would have already terminated the current routine. The debugger itself can also be customized or replaced using the.debugger-hook.
dynamic variable. Code found within unwind-protect forms such as finalizers will also be executed as appropriate despite the exception.In the following example (using ) the user tries to open a file in a Lisp function test called from the Read-Eval-Print-LOOP , when the file does not exist. The Lisp system presents four restarts. The user selects the Retry OPEN using a different pathname restart and enters a different pathname (lispm-init.lisp instead of lispm-int.lisp).
The user code does not contain any error handling code. The whole error handling and restart code is provided by the Lisp system, which can handle and repair the error without terminating the user code. Command: (test 'zippylispm-int.lisp')Error: The file was not found.For lispm:zippylispm-int.lisp.newestLMFS:OPEN-LOCAL-LMFS-1Arg 0: #P'lispm:zippylispm-int.lisp.newest's-A,: Retry OPEN of lispm:zippylispm-int.lisp.newests-B: Retry OPEN using a different pathnames-C,: Return to Lisp Top Level in a TELNET servers-D: Restart process TELNET terminal- Retry OPEN using a different pathnameUse what pathname instead default lispm:zippylispm-int.lisp.newest:lispm:zippylispm-init.lisp.newest.the program continuesCommon Lisp Object System (CLOS). Main article:Common Lisp includes a toolkit for, the Common Lisp Object System or, which is one of the most powerful object systems available in any language. For example, explains how many are simpler to implement in a dynamic language with the features of CLOS (Multiple Inheritance, Mixins, Multimethods, Metaclasses, Method combinations, etc.).Several extensions to Common Lisp for object-oriented programming have been proposed to be included into the ANSI Common Lisp standard, but eventually CLOS was adopted as the standard object-system for Common Lisp.
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CLOS is a object system with and, and differs radically from the OOP facilities found in static languages such as. As a dynamic object system, CLOS allows changes at runtime to generic functions and classes.
Methods can be added and removed, classes can be added and redefined, objects can be updated for class changes and the class of objects can be changed.CLOS has been integrated into ANSI Common Lisp. Generic functions can be used like normal functions and are a first-class data type. Every CLOS class is integrated into the Common Lisp type system. Many Common Lisp types have a corresponding class.
There is more potential use of CLOS for Common Lisp. The specification does not say whether conditions are implemented with CLOS. Pathnames and streams could be implemented with CLOS.
These further usage possibilities of CLOS for ANSI Common Lisp are not part of the standard. Actual Common Lisp implementations use CLOS for pathnames, streams, input–output, conditions, the implementation of CLOS itself and more.Compiler and interpreter A Lisp interpreter directly executes Lisp source code provided as Lisp objects (lists, symbols, numbers.) read from s-expressions. A Lisp compiler generates or from Lisp source code. Common Lisp allows both individual Lisp functions to be compiled in memory and the compilation of whole files to externally stored compiled code ( fasl files).Several implementations of earlier Lisp dialects provided both an interpreter and a compiler. Unfortunately often the semantics were different.
These earlier Lisps implemented lexical scoping in the compiler and dynamic scoping in the interpreter. Common Lisp requires that both the interpreter and compiler use lexical scoping by default. The Common Lisp standard describes both the semantics of the interpreter and a compiler. The compiler can be called using the function compile for individual functions and using the function compile-file for files. Common Lisp allows type declarations and provides ways to influence the compiler code generation policy. For the latter various optimization qualities can be given values between 0 (not important) and 3 (most important): speed, space, safety, debug and compilation-speed.There is also a function to evaluate Lisp code: eval. Eval takes code as pre-parsed s-expressions and not, like in some other languages, as text strings.
This way code can be constructed with the usual Lisp functions for constructing lists and symbols and then this code can be evaluated with the function eval. Several Common Lisp implementations (like Clozure CL and SBCL) are implementing eval using their compiler. This way code is compiled, even though it is evaluated using the function eval.The file compiler is invoked using the function compile-file. The generated file with compiled code is called a fasl (from fast load) file. These fasl files and also source code files can be loaded with the function load into a running Common Lisp system.
Depending on the implementation, the file compiler generates byte-code (for example for the ), code (which then is compiled with a C compiler) or, directly, native code.Common Lisp implementations can be used interactively, even though the code gets fully compiled. The idea of an thus does not apply for interactive Common Lisp.The language makes distinction between read-time, compile-time, load-time and run-time, and allows user code to also make this distinction to perform the wanted type of processing at the wanted step.Some special operators are provided to especially suit interactive development; for instance, defvar will only assign a value to its provided variable if it wasn't already bound, while defparameter will always perform the assignment. This distinction is useful when interactively evaluating, compiling and loading code in a live image.Some features are also provided to help writing compilers and interpreters. Symbols consist of first-level objects and are directly manipulable by user code. The progv special operator allows to create lexical bindings programmatically, while packages are also manipulable. The Lisp compiler is available at runtime to compile files or individual functions. These make it easy to use Lisp as an intermediate compiler or interpreter for another language.Code examples Birthday paradox The following program calculates the smallest number of people in a room for whom the probability of completely unique birthdays is less than 50% (the, where for 1 person the probability is obviously 100%, for 2 it is 364/365, etc.).
The answer is 23.By convention, constants in Common Lisp are enclosed with + characters. ( defclass person (( name:initarg:name:accessor person-name ) ( age:initarg:age:accessor person-age )) (:documentation 'The class PERSON with slots NAME and AGE.' )) ( defmethod display (( object person ) stream ) 'Displaying a PERSON object to an output stream.' ( with-slots ( name age ) object ( format stream 'a (a)' name age ))) ( defparameter.group. ( list ( make-instance 'person:name 'Bob':age 33 ) ( make-instance 'person:name 'Chris':age 16 ) ( make-instance 'person:name 'Ash':age 23 )) 'A list of PERSON objects.'
) ( dolist ( person ( sort ( copy-list.group. ) #' :key #' person-age )) ( display person.standard-output.
) ( terpri ))It prints the three names with descending age. ( defun list-matching-lines ( file predicate ) 'Returns a list of lines in file, for which the predicate applied to the line returns T.' ( with-open-file ( stream file ) ( loop for line = ( read-line stream nil nil ) while line when ( funcall predicate line ) collect it )))The function AVAILABLE-SHELLS calls above function LIST-MATCHING-LINES with a pathname and an anonymous function as the predicate. The predicate returns the pathname of a shell or NIL (if the string is not the filename of a shell). CL-USER ( available-shells ) ( #P'/bin/bash' #P'/bin/csh' #P'/bin/ksh' #P'/bin/sh' #P'/bin/tcsh' #P'/bin/zsh' ) Comparison with other Lisps Common Lisp is most frequently compared with, and contrasted to, —if only because they are the two most popular Lisp dialects. Scheme predates CL, and comes not only from the same Lisp tradition but from some of the same engineers—, with whom designed Scheme, chaired the standards committee for Common Lisp.Common Lisp is a general-purpose programming language, in contrast to Lisp variants such as and which are embedded in particular products (GNU Emacs and AutoCAD, respectively).
Unlike many earlier Lisps, Common Lisp (like ) uses lexical variable by default for both interpreted and compiled code.Most of the Lisp systems whose designs contributed to Common Lisp—such as and Franz Lisp—used dynamically variables in their interpreters and lexically scoped variables in their compilers. Scheme introduced the sole use of lexically scoped variables to Lisp; an inspiration from which was widely recognized as a good idea. CL supports dynamically scoped variables as well, but they must be explicitly declared as 'special'. There are no differences in scoping between ANSI CL interpreters and compilers.Common Lisp is sometimes termed a Lisp-2 and Scheme a Lisp-1, referring to CL's use of separate namespaces for functions and variables. (In fact, CL has many namespaces, such as those for go tags, block names, and loop keywords). There is a long-standing controversy between CL and Scheme advocates over the tradeoffs involved in multiple namespaces. In Scheme, it is (broadly) necessary to avoid giving variables names which clash with functions; Scheme functions frequently have arguments named lis, lst, or lyst so as not to conflict with the system function list.
However, in CL it is necessary to explicitly refer to the function namespace when passing a function as an argument—which is also a common occurrence, as in the sort example above.CL also differs from Scheme in its handling of boolean values. Scheme uses the special values #t and #f to represent truth and falsity. CL follows the older Lisp convention of using the symbols T and NIL, with NIL standing also for the empty list. In CL, any non-NIL value is treated as true by conditionals, such as if, whereas in Scheme all non-#f values are treated as true. These conventions allow some operators in both languages to serve both as predicates (answering a boolean-valued question) and as returning a useful value for further computation, but in Scheme the value ' which is equivalent to NIL in Common Lisp evaluates to true in a boolean expression.Lastly, the Scheme standards documents require, which the CL standard does not. Most CL implementations do offer tail-call optimization, although often only when the programmer uses an optimization directive.
Nonetheless, common CL coding style does not favor the ubiquitous use of recursion that Scheme style prefers—what a Scheme programmer would express with tail recursion, a CL user would usually express with an iterative expression in do, dolist, loop, or (more recently) with the iterate package.Implementations See the Category.Common Lisp is defined by a specification (like and ) rather than by one implementation (like before version 6). This section needs additional citations for.
Unsourced material may be challenged and removed.Find sources: – ( July 2018) Austin Kyoto Common Lisp an evolution of by Butterfly Common Lisp an implementation written in Scheme for the multi-processor computer CLICC a Common Lisp to C compiler CLOE Common Lisp for PCs by Codemist Common Lisp used for the commercial version of the computer algebra system Axiom ExperCommon Lisp an early implementation for the Apple Macintosh by ExperTelligence an implementation for the PC by GoldHill Inc. Ibuki Common Lisp a commercialized version of Kyoto Common Lisp the first Common Lisp compiler that used C as a target language. GCL, ECL and MKCL originate from this Common Lisp implementation. L a small version of Common Lisp for embedded systems developed by IS Robotics, now iRobot (from, TI and Xerox ) provided implementations of Common Lisp in addition to their native Lisp dialect (Lisp Machine Lisp or Interlisp).
CLOS was also available. Symbolics provides an enhanced version Common Lisp. Quoted from cover of cited standard. ANSI INCITS 226-1994 (R2004), for sale on standard's 2014-01-01 at the. Archived from on 2012-04-21. Retrieved 2007-12-22. Retrieved 2015-05-13.
Cl-su-ai.lisp.se. 2012-08-08 at the. Jr, Steele; L, Guy (15 August 1982). – via dl.acm.org. Reddy, Abhishek (2008-08-22). The Common Lisp Wiki. Retrieved 2008-08-21.
Richard P. Gabriel; Kent M. Pitman (June 1988). Lisp and Symbolic Computation. 1 (1): 81–101. Letoverlambda.com. Peter Seibel (7 April 2005).
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(22 June 1992). 'CLICC: A New Approach to the Compilation of Common Lisp Programs to C'. Cite journal requires journal=. Goldhill-inc.com.
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Huffman, Steve. Retrieved 11 May 2019. Quicklisp description. Library count can be directly obtained by executing (length (ql:system-list)) in a Lisp REPL that has loaded the Quicklisp system. Count as of 2019-03-11 is 4087 packages.
Getting a library into QuicklispBibliography A chronological list of books published (or about to be published) about Common Lisp (the language) or about programming with Common Lisp (especially AI programming).: Common Lisp the Language, 1st Edition, Digital Press, 1984,.: Programming in Common Lisp, John Wiley and Sons Inc, 1985,.: Performance and Evaluation of Lisp Systems, The MIT Press, 1985,.: Common LISPcraft, W.W.