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76-635: SNOBOL4 stands apart from most programming languages of its era by having patterns as a first-class data type ( i.e. a data type whose values can be manipulated in all ways permitted to any other data type in the programming language) and by providing operators for pattern concatenation and alternation . SNOBOL4 patterns are a type of object and admit various manipulations, much like later object-oriented languages such as JavaScript whose patterns are known as regular expressions . In addition SNOBOL4 strings generated during execution can be treated as programs and either interpreted or compiled and executed (as in

152-426: A u {\displaystyle u} is called an upper bound of S . {\displaystyle S.} So, Dedekind completeness means that, if S is bounded above, it has an upper bound that is less than any other upper bound. Dedekind completeness implies other sorts of completeness (see below), but also has some important consequences. The last two properties are summarized by saying that

228-440: A , {\displaystyle D_{n-1}+a_{n}/10^{n}\leq a,} and one sets D n = D n − 1 + a n / 10 n . {\displaystyle D_{n}=D_{n-1}+a_{n}/10^{n}.} One can use the defining properties of the real numbers to show that x is the least upper bound of the D n . {\displaystyle D_{n}.} So,

304-452: A Snowball's chance in hell of finding a name". All of us yelled at once, "WE GOT IT — SNOBOL" in the spirit of all the BOL languages . We then stretched our mind to find what it stood for. Common backronyms of "SNOBOL" are 'String Oriented Symbolic Language' or (as a quasi-initialism ) 'StriNg Oriented symBOlic Language'. First-class object In a given programming language design ,

380-480: A decimal point , representing the infinite series For example, for the circle constant π = 3.14159 ⋯ , {\displaystyle \pi =3.14159\cdots ,} k is zero and b 0 = 3 , {\displaystyle b_{0}=3,} a 1 = 1 , {\displaystyle a_{1}=1,} a 2 = 4 , {\displaystyle a_{2}=4,} etc. More formally,

456-406: A decimal representation for a nonnegative real number x consists of a nonnegative integer k and integers between zero and nine in the infinite sequence (If k > 0 , {\displaystyle k>0,} then by convention b k ≠ 0. {\displaystyle b_{k}\neq 0.} ) Such a decimal representation specifies the real number as

532-540: A first-class citizen is an entity which supports all the operations generally available to other entities. These operations typically include being passed as an argument , returned from a function , and assigned to a variable . The concept of first- and second-class objects was introduced by Christopher Strachey in the 1960s. He did not actually define the term strictly, but contrasted real numbers and procedures in ALGOL : First and second class objects. In ALGOL,

608-443: A line called the number line or real line , where the points corresponding to integers ( ..., −2, −1, 0, 1, 2, ... ) are equally spaced. Conversely, analytic geometry is the association of points on lines (especially axis lines ) to real numbers such that geometric displacements are proportional to differences between corresponding numbers. The informal descriptions above of the real numbers are not sufficient for ensuring

684-593: A power of ten , extending to finitely many positive powers of ten to the left and infinitely many negative powers of ten to the right. For a number x whose decimal representation extends k places to the left, the standard notation is the juxtaposition of the digits b k b k − 1 ⋯ b 0 . a 1 a 2 ⋯ , {\displaystyle b_{k}b_{k-1}\cdots b_{0}.a_{1}a_{2}\cdots ,} in descending order by power of ten, with non-negative and negative powers of ten separated by

760-486: A total order that have the following properties. Many other properties can be deduced from the above ones. In particular: Several other operations are commonly used, which can be deduced from the above ones. The total order that is considered above is denoted a < b {\displaystyle a<b} and read as " a is less than b ". Three other order relations are also commonly used: The real numbers 0 and 1 are commonly identified with

836-465: A virtual machine to allow improved portability across computers. The SNOBOL4 language translator was still written in assembly language. However the macro features of the assembler were used to define the virtual machine instructions of the S NOBOL I mplementation L anguage, the SIL. This very much improved the portability of the language by making it relatively easy to port the virtual machine which hosted

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912-452: A characterization of the real numbers.) It is not true that R {\displaystyle \mathbb {R} } is the only uniformly complete ordered field, but it is the only uniformly complete Archimedean field , and indeed one often hears the phrase "complete Archimedean field" instead of "complete ordered field". Every uniformly complete Archimedean field must also be Dedekind-complete (and vice versa), justifying using "the" in

988-409: A conditional branch dependent upon the success or failure of the subject evaluation, the pattern evaluation, the pattern match, the object evaluation or the final assignment. It can also be a transfer to code created and compiled by the program itself during a run. A SNOBOL pattern can be very simple or extremely complex. A simple pattern is just a text string (e.g. "ABCD"), but a complex pattern may be

1064-457: A large structure describing, for example, the complete grammar of a computer language. It is possible to implement a language interpreter in SNOBOL almost directly from a Backus–Naur form expression of it, with few changes. Creating a macro assembler and an interpreter for a completely theoretical piece of hardware could take as little as a few hundred lines, with a new instruction being added with

1140-405: A limit, without computing it, and even without knowing it. For example, the standard series of the exponential function converges to a real number for every x , because the sums can be made arbitrarily small (independently of M ) by choosing N sufficiently large. This proves that the sequence is Cauchy, and thus converges, showing that e x {\displaystyle e^{x}}

1216-459: A nonnegative real number x , one can define a decimal representation of x by induction , as follows. Define b k ⋯ b 0 {\displaystyle b_{k}\cdots b_{0}} as decimal representation of the largest integer D 0 {\displaystyle D_{0}} such that D 0 ≤ x {\displaystyle D_{0}\leq x} (this integer exists because of

1292-473: A rational number is an equivalence class of pairs of integers, and a real number is an equivalence class of Cauchy series), and are generally harmless. It is only in very specific situations, that one must avoid them and replace them by using explicitly the above homomorphisms. This is the case in constructive mathematics and computer programming . In the latter case, these homomorphisms are interpreted as type conversions that can often be done automatically by

1368-569: A real number may appear in an expression or be assigned to a variable, and either of them may appear as an actual parameter in a procedure call. A procedure, on the other hand, may only appear in another procedure call either as the operator (the most common case) or as one of the actual parameters. There are no other expressions involving procedures or whose results are procedures. Thus in a sense procedures in ALGOL are second class citizens—they always have to appear in person and can never be represented by

1444-452: A result, several incompatible dialects arose. As SNOBOL3 became more popular, the authors received more and more requests for extensions to the language. They also began to receive complaints about incompatibility and bugs in versions that they hadn't written. To address this and to take advantage of the new computers being introduced in the late 1960s, the decision was taken to develop SNOBOL4 with many extra datatypes and features but based on

1520-463: A result, the authors decided to extend it and tidy it up. SNOBOL2 did exist but it was a short-lived intermediate development version without user-defined functions and was never released. SNOBOL was rewritten to add functions, both standard and user-defined, and the result was released as SNOBOL3. SNOBOL3 became quite popular and was rewritten for other computers than the IBM 7090 by other programmers. As

1596-583: A single garbage-collected heap. The "Hello, World!" program might be as follows... A simple program to ask for a user's name and then use it in an output sentence... To choose between three possible outputs... To continue requesting input until no more is forthcoming... The classic implementation was on the PDP-10 ; it has been used to study compilers , formal grammars , and artificial intelligence , especially machine translation and machine comprehension of natural languages . The original implementation

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1672-405: A single line. Complex SNOBOL patterns can do things that would be impractical or impossible using the more primitive regular expressions used in most other pattern-matching languages. Some of this power derives from the so-called "SPITBOL extensions" (which have since been incorporated in basically all modern implementations of the original SNOBOL 4 language too), although it is possible to achieve

1748-553: A subroutine. For example, neither Fortran IV nor C supports array assignment, and when they are passed as parameters, only the position of their first element is actually passed—their size is lost. C appears to support assignment of array pointers , but in fact these are simply pointers to the array's first element, and again do not carry the array's size. In most languages, data types are not first-class objects, though in some object-oriented languages, classes are first-class objects and are instances of metaclasses . Languages in

1824-615: A variable or expression (except in the case of a formal parameter)... Robin Popplestone gave the following definition: All items have certain fundamental rights. During the 1990s, Raphael Finkel proposed definitions of second and third class values, but these definitions have not been widely adopted. The simplest scalar data types, such as integer and floating-point numbers, are nearly always first-class. In many older languages, arrays and strings are not first-class: they cannot be assigned as objects or passed as parameters to

1900-678: A way to express BNF grammars, which are equivalent to context-free grammars and more powerful than regular expressions. The "regular expressions" in current versions of AWK and Perl are in fact extensions of regular expressions in the traditional sense , but regular expressions, unlike SNOBOL4 patterns, are not recursive, which gives a distinct computational advantage to SNOBOL4 patterns. (Recursive expressions did appear in Perl 5.10 , though, released in December 2007.) The later SL5 (1977) and Icon (1978) languages were designed by Griswold to combine

1976-711: Is disputed. Some authors require it be possible to create new functions at runtime to call them 'first-class'. Under this definition, functions in C are not first-class objects; instead, they are sometimes called second-class objects , because they can still be manipulated in most of the above fashions (via function pointers ). In Smalltalk , functions (methods) are first-class objects, just like Smalltalk classes. Since Smalltalk operators (+, -, etc.) are methods, they are also first-class objects. Some languages, such as Java and PHP , have an explicit reflection subsystem which allow access to internal implementation structures even though they are not accessible or manipulable in

2052-459: Is distinctive in format and programming style, which are radically different from contemporary procedural languages such as Fortran and ALGOL . SNOBOL4 supports a number of built-in data types , such as integers and limited precision real numbers , strings , patterns , arrays , and tables (associative arrays), and also allows the programmer to define additional data types and new functions . SNOBOL4's programmer-defined data type facility

2128-435: Is less than ε for all n and m that are both greater than N . This definition, originally provided by Cauchy , formalizes the fact that the x n eventually come and remain arbitrarily close to each other. A sequence ( x n ) converges to the limit x if its elements eventually come and remain arbitrarily close to x , that is, if for any ε > 0 there exists an integer N (possibly depending on ε) such that

2204-402: Is practical to even attempt using regular expressions. SNOBOL4 pattern-matching uses a backtracking algorithm similar to that used in the logic programming language Prolog , which provides pattern-like constructs via DCGs . This algorithm makes it easier to use SNOBOL as a logic programming language than is the case for most languages. SNOBOL stores variables, strings and data structures in

2280-487: Is so that many sequences have limits . More formally, the reals are complete (in the sense of metric spaces or uniform spaces , which is a different sense than the Dedekind completeness of the order in the previous section): A sequence ( x n ) of real numbers is called a Cauchy sequence if for any ε > 0 there exists an integer N (possibly depending on ε) such that the distance | x n − x m |

2356-458: Is well defined for every x . The real numbers are often described as "the complete ordered field", a phrase that can be interpreted in several ways. First, an order can be lattice-complete . It is easy to see that no ordered field can be lattice-complete, because it can have no largest element (given any element z , z + 1 is larger). Additionally, an order can be Dedekind-complete, see § Axiomatic approach . The uniqueness result at

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2432-495: Is what mathematicians and physicists did during several centuries before the first formal definitions were provided in the second half of the 19th century. See Construction of the real numbers for details about these formal definitions and the proof of their equivalence. The real numbers form an ordered field . Intuitively, this means that methods and rules of elementary arithmetic apply to them. More precisely, there are two binary operations , addition and multiplication , and

2508-661: The Michigan Terminal System (MTS) provided pattern matching based on SNOBOL4 patterns. Several implementations are currently available. Macro SNOBOL4 in C written by Phil Budne is a free, open source implementation, capable of running on almost any platform. Catspaw, Inc provided a commercial implementation of the SNOBOL4 language for many different computer platforms, including DOS, Macintosh, Sun, RS/6000, and others, and these implementations are now available free from Catspaw. Minnesota SNOBOL4, by Viktors Berstis,

2584-643: The compiler . Previous properties do not distinguish real numbers from rational numbers . This distinction is provided by Dedekind completeness , which states that every set of real numbers with an upper bound admits a least upper bound . This means the following. A set of real numbers S {\displaystyle S} is bounded above if there is a real number u {\displaystyle u} such that s ≤ u {\displaystyle s\leq u} for all s ∈ S {\displaystyle s\in S} ; such

2660-413: The eval function of other languages). SNOBOL4 was quite widely taught in larger U.S. universities in the late 1960s and early 1970s and was widely used in the 1970s and 1980s as a text manipulation language in the humanities . In the 1980s and 1990s, its use faded as newer languages such as AWK and Perl made string manipulation by means of regular expressions fashionable. SNOBOL4 patterns include

2736-531: The functional programming family often also feature first-class types, in the form of, for example, generalized algebraic data types , or other metalanguage amenities enabling programs to implement extensions to their own implementation language. Few languages support continuations and GOTO -labels as objects at all, let alone as first-class objects. Many programming languages support passing and returning function values, which can be applied to arguments. Whether this suffices to call function values first-class

2812-422: The natural numbers 0 and 1 . This allows identifying any natural number n with the sum of n real numbers equal to 1 . This identification can be pursued by identifying a negative integer − n {\displaystyle -n} (where n {\displaystyle n} is a natural number) with the additive inverse − n {\displaystyle -n} of

2888-570: The square roots of −1 . The real numbers include the rational numbers , such as the integer −5 and the fraction 4 / 3 . The rest of the real numbers are called irrational numbers . Some irrational numbers (as well as all the rationals) are the root of a polynomial with integer coefficients, such as the square root √2 = 1.414... ; these are called algebraic numbers . There are also real numbers which are not, such as π = 3.1415... ; these are called transcendental numbers . Real numbers can be thought of as all points on

2964-511: The Archimedean property). Then, supposing by induction that the decimal fraction D i {\displaystyle D_{i}} has been defined for i < n , {\displaystyle i<n,} one defines a n {\displaystyle a_{n}} as the largest digit such that D n − 1 + a n / 10 n ≤

3040-529: The axiomatic definition and are thus equivalent. Real numbers are completely characterized by their fundamental properties that can be summarized by saying that they form an ordered field that is Dedekind complete . Here, "completely characterized" means that there is a unique isomorphism between any two Dedekind complete ordered fields, and thus that their elements have exactly the same properties. This implies that one can manipulate real numbers and compute with them, without knowing how they can be defined; this

3116-441: The axioms of Zermelo–Fraenkel set theory including the axiom of choice (ZFC)—the standard foundation of modern mathematics. In fact, some models of ZFC satisfy CH, while others violate it. As a topological space, the real numbers are separable . This is because the set of rationals, which is countable, is dense in the real numbers. The irrational numbers are also dense in the real numbers, however they are uncountable and have

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3192-549: The backtracking of SNOBOL4 pattern matching with more standard ALGOL -like structuring. The initial SNOBOL language was created as a tool to be used by its authors to work with the symbolic manipulation of polynomials. It was written in assembly language for the IBM 7090 . It had a simple syntax, only one datatype, the string, no functions, and no declarations and very little error control. However, despite its simplicity and its "personal" nature its use began to spread to other groups. As

3268-420: The cardinality of the power set of the set of the natural numbers. The statement that there is no subset of the reals with cardinality strictly greater than ℵ 0 {\displaystyle \aleph _{0}} and strictly smaller than c {\displaystyle {\mathfrak {c}}} is known as the continuum hypothesis (CH). It is neither provable nor refutable using

3344-411: The classical definitions of limits , continuity and derivatives . The set of real numbers, sometimes called "the reals", is traditionally denoted by a bold R , often using blackboard bold , ⁠ R {\displaystyle \mathbb {R} } ⁠ . The adjective real , used in the 17th century by René Descartes , distinguishes real numbers from imaginary numbers such as

3420-458: The closest PC implementation to the original IBM mainframe version (even including Fortran-like FORMAT statement support) is also free. Although SNOBOL itself has no structured programming features, a SNOBOL preprocessor called Snostorm was designed and implemented during the 1970s by Fred G. Swartz for use under the Michigan Terminal System (MTS) at the University of Michigan . Snostorm

3496-439: The construction of the reals from surreal numbers , since that construction starts with a proper class that contains every ordered field (the surreals) and then selects from it the largest Archimedean subfield. The set of all real numbers is uncountable , in the sense that while both the set of all natural numbers {1, 2, 3, 4, ...} and the set of all real numbers are infinite sets , there exists no one-to-one function from

3572-613: The core programming system by users can easily undermine performance optimisations made by language implementers. Real number In mathematics , a real number is a number that can be used to measure a continuous one- dimensional quantity such as a distance , duration or temperature . Here, continuous means that pairs of values can have arbitrarily small differences. Every real number can be almost uniquely represented by an infinite decimal expansion . The real numbers are fundamental in calculus (and in many other branches of mathematics), in particular by their role in

3648-652: The correctness of proofs of theorems involving real numbers. The realization that a better definition was needed, and the elaboration of such a definition was a major development of 19th-century mathematics and is the foundation of real analysis , the study of real functions and real-valued sequences . A current axiomatic definition is that real numbers form the unique ( up to an isomorphism ) Dedekind-complete ordered field . Other common definitions of real numbers include equivalence classes of Cauchy sequences (of rational numbers), Dedekind cuts , and infinite decimal representations . All these definitions satisfy

3724-417: The distance | x n − x | is less than ε for n greater than N . Every convergent sequence is a Cauchy sequence, and the converse is true for real numbers, and this means that the topological space of the real numbers is complete. The set of rational numbers is not complete. For example, the sequence (1; 1.4; 1.41; 1.414; 1.4142; 1.41421; ...), where each term adds a digit of the decimal expansion of

3800-496: The end of that section justifies using the word "the" in the phrase "complete ordered field" when this is the sense of "complete" that is meant. This sense of completeness is most closely related to the construction of the reals from Dedekind cuts, since that construction starts from an ordered field (the rationals) and then forms the Dedekind-completion of it in a standard way. These two notions of completeness ignore

3876-516: The entire semester was focused on implementing SITBOL. It was over 80% complete by the end of the semester and was subsequently completed by Professor Gimpel and several students over the summer. SITBOL was a full-featured, high-performance SNOBOL4 interpreter. The Gnat Ada Compiler comes with a package (GNAT.Spitbol) that implements all of the Spitbol string manipulation semantics. This can be called from within an Ada program. The file editor for

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3952-543: The equivalent capabilities normally thought of as "structured programming", most notably nested if/then/else type constructs. These features have since been added to most recent SNOBOL4 implementations. After many years as a commercial product, in April 2009 SPITBOL was released as free software under the GNU General Public License . According to Dave Farber, he, Griswold and Polonsky "finally arrived at

4028-534: The facilities that the interpreter provides. The classic implementation on the PDP-10 was quite slow, and in 1972 James Gimpel of Bell Labs, Holmdel, N.J. designed a native implementation of SNOBOL4 for the PDP-10 that he named SITBOL. He used the design as the basis of a graduate class in string processing that he taught that year at Stevens Institute of Technology (which is why it was named SITBOL). Students were given sections to implement (in PDP-10 assembler) and

4104-427: The field structure. However, an ordered group (in this case, the additive group of the field) defines a uniform structure, and uniform structures have a notion of completeness ; the description in § Completeness is a special case. (We refer to the notion of completeness in uniform spaces rather than the related and better known notion for metric spaces , since the definition of metric space relies on already having

4180-800: The first decimal representation, all a n {\displaystyle a_{n}} are zero for n > h , {\displaystyle n>h,} and, in the second representation, all a n {\displaystyle a_{n}} 9. (see 0.999... for details). In summary, there is a bijection between the real numbers and the decimal representations that do not end with infinitely many trailing 9. The preceding considerations apply directly for every numeral base B ≥ 2 , {\displaystyle B\geq 2,} simply by replacing 10 with B {\displaystyle B} and 9 with B − 1. {\displaystyle B-1.} A main reason for using real numbers

4256-556: The identification of natural numbers with some real numbers is justified by the fact that Peano axioms are satisfied by these real numbers, with the addition with 1 taken as the successor function . Formally, one has an injective homomorphism of ordered monoids from the natural numbers N {\displaystyle \mathbb {N} } to the integers Z , {\displaystyle \mathbb {Z} ,} an injective homomorphism of ordered rings from Z {\displaystyle \mathbb {Z} } to

4332-408: The least upper bound of the decimal fractions that are obtained by truncating the sequence: given a positive integer n , the truncation of the sequence at the place n is the finite partial sum The real number x defined by the sequence is the least upper bound of the D n , {\displaystyle D_{n},} which exists by Dedekind completeness. Conversely, given

4408-609: The metric topology as epsilon-balls. The Dedekind cuts construction uses the order topology presentation, while the Cauchy sequences construction uses the metric topology presentation. The reals form a contractible (hence connected and simply connected ), separable and complete metric space of Hausdorff dimension  1. The real numbers are locally compact but not compact . There are various properties that uniquely specify them; for instance, all unbounded, connected, and separable order topologies are necessarily homeomorphic to

4484-647: The name Symbolic EXpression Interpreter SEXI." All went well until one day I was submitting a batch job to assemble the system and as normal on my JOB card — the first card in the deck, I, in BTL standards, punched my job and my name — SEXI Farber. One of the Comp Center girls looked at it and said, "That's what you think" in a humorous way. That made it clear that we needed another name!! We sat and talked and drank coffee and shot rubber bands and after much too much time someone said — most likely Ralph — "We don't have

4560-400: The pattern itself during the matching operation. Patterns can be saved like any other first-class data item, and can be concatenated, used within other patterns, and used to create very complex and sophisticated pattern expressions. It is possible to write, for example, a SNOBOL4 pattern which matches "a complete name and international postal mailing address", which is well beyond anything that

4636-464: The phrase "the complete Archimedean field". This sense of completeness is most closely related to the construction of the reals from Cauchy sequences (the construction carried out in full in this article), since it starts with an Archimedean field (the rationals) and forms the uniform completion of it in a standard way. But the original use of the phrase "complete Archimedean field" was by David Hilbert , who meant still something else by it. He meant that

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4712-399: The positive square root of 2, is Cauchy but it does not converge to a rational number (in the real numbers, in contrast, it converges to the positive square root of 2). The completeness property of the reals is the basis on which calculus , and more generally mathematical analysis , are built. In particular, the test that a sequence is a Cauchy sequence allows proving that a sequence has

4788-492: The rational numbers Q , {\displaystyle \mathbb {Q} ,} and an injective homomorphism of ordered fields from Q {\displaystyle \mathbb {Q} } to the real numbers R . {\displaystyle \mathbb {R} .} The identifications consist of not distinguishing the source and the image of each injective homomorphism, and thus to write These identifications are formally abuses of notation (since, formally,

4864-533: The rational numbers an ordered subfield of the real numbers R . {\displaystyle \mathbb {R} .} The Dedekind completeness described below implies that some real numbers, such as 2 , {\displaystyle {\sqrt {2}},} are not rational numbers; they are called irrational numbers . The above identifications make sense, since natural numbers, integers and real numbers are generally not defined by their individual nature, but by defining properties ( axioms ). So,

4940-464: The real number identified with n . {\displaystyle n.} Similarly a rational number p / q {\displaystyle p/q} (where p and q are integers and q ≠ 0 {\displaystyle q\neq 0} ) is identified with the division of the real numbers identified with p and q . These identifications make the set Q {\displaystyle \mathbb {Q} } of

5016-436: The real numbers form a real closed field . This implies the real version of the fundamental theorem of algebra , namely that every polynomial with real coefficients can be factored into polynomials with real coefficients of degree at most two. The most common way of describing a real number is via its decimal representation , a sequence of decimal digits each representing the product of an integer between zero and nine times

5092-417: The real numbers form the largest Archimedean field in the sense that every other Archimedean field is a subfield of R {\displaystyle \mathbb {R} } . Thus R {\displaystyle \mathbb {R} } is "complete" in the sense that nothing further can be added to it without making it no longer an Archimedean field. This sense of completeness is most closely related to

5168-429: The real numbers to the natural numbers. The cardinality of the set of all real numbers is denoted by c . {\displaystyle {\mathfrak {c}}.} and called the cardinality of the continuum . It is strictly greater than the cardinality of the set of all natural numbers (denoted ℵ 0 {\displaystyle \aleph _{0}} and called 'aleph-naught' ), and equals

5244-496: The resulting sequence of digits is called a decimal representation of x . Another decimal representation can be obtained by replacing ≤ x {\displaystyle \leq x} with < x {\displaystyle <x} in the preceding construction. These two representations are identical, unless x is a decimal fraction of the form m 10 h . {\textstyle {\frac {m}{10^{h}}}.} In this case, in

5320-425: The same cardinality as the reals. The real numbers form a metric space : the distance between x and y is defined as the absolute value | x − y | . By virtue of being a totally ordered set, they also carry an order topology ; the topology arising from the metric and the one arising from the order are identical, but yield different presentations for the topology—in the order topology as ordered intervals, in

5396-438: The same power without them. Part of this power comes from the side effects that it is possible to produce during the pattern matching operation, including saving numerous intermediate/tentative matching results and the ability to invoke user-written functions during the pattern match which can perform nearly any desired processing, and then influence the ongoing direction the interrupted pattern match takes, or even to indeed change

5472-607: The same way as ordinary objects. In other languages, such as those in the Lisp family, reflection is a central feature of the language, rather than a special subsystem. Typically this takes the form of some set of the following features: These allow varying forms of first-class access to the language implementation, and are, in general, manipulable in the same way as, and fully indistinguishable from, ordinary language objects. Because of this, their usage generally comes with some (cultural) stipulations and advice, as untested modification of

5548-428: The translator by recreating its virtual instructions on any machine which included a macro assembler or indeed a high level language. The machine-independent language SIL arose as a generalization of string manipulation macros by Douglas McIlroy , which were used extensively in the initial SNOBOL implementation. In 1969, McIlroy influenced the language again by insisting on addition of the table type to SNOBOL4. SNOBOL

5624-419: Was advanced at the time—it is similar to the records of the earlier COBOL and the later Pascal programming languages. All SNOBOL command lines are of the form Each of the five elements is optional. In general, the subject is matched against the pattern . If the object is present, any matched portion is replaced by the object via rules for replacement. The transfer can be an absolute branch or

5700-502: Was on an IBM 7090 at Bell Labs, Holmdel, N.J. SNOBOL4 was specifically designed for portability; the first implementation was started on an IBM 7094 in 1966 but completed on an IBM 360 in 1967. It was rapidly ported to many other platforms. It is normally implemented as an interpreter because of the difficulty in implementing some of its very high-level features, but there is a compiler , the SPITBOL compiler , which provides nearly all

5776-491: Was used at the eight to fifteen sites that ran MTS. It was also available at University College London (UCL) between 1982 and 1984. Snocone by Andrew Koenig adds block-structured constructs to the SNOBOL4 language. Snocone is a self-contained programming language, rather than a proper superset of SNOBOL4. The SPITBOL implementation also introduced a number of features which, while not using traditional structured programming keywords, nevertheless can be used to provide many of

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