A regular expression , regex or regexp is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation. It is a technique developed in theoretical computer science and formal language theory. Icon is a very high-level programming language featuring goal-directed execution and many facilities for managing strings and textual patterns.
Icon is not object-oriented, but an object-oriented extension called Idol was developed in which eventually became Unicon. ALGOL is a family of imperative computer programming languages, originally developed in the mids, which greatly influenced many other languages and was the standard method for algorithm description used by the ACM in textbooks and academic sources for more than thirty years.
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 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 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. As a result, several incompatible dialects arose. The IBM is a second-generation transistorized version of the earlier IBM vacuum tube mainframe computer that was designed for "large-scale scientific and technological applications".
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The first installation was in December 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 s, the decision was taken to develop SNOBOL4 with many extra datatypes and features but based on a virtual machine to allow improved portability across computers. This very much improved the portability of the language by making it relatively easy to port the virtual machine which hosted the translator by recreating its virtual instructions on any machine which included a macro assembler or indeed a high level language.
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. 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 SNOBOL Programming Language
The transfer can be an absolute branch or 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 simple pattern is just a text string e. 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 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 the same power without them.
Humanist Archives Vol. 10 : etext and SNOBOL
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 is practical to even attempt using regular expressions.
The classic implementation was on the PDP ; it has been used to study compilers , formal grammars , and artificial intelligence , especially machine translation and machine comprehension of natural languages. 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 the facilities that the interpreter provides.
Spitbol which implements all of the Spitbol string manipulation semantics. This can be called from within an Ada program.
Several implementations are currently available. 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 a Snowball's chance in hell of finding a name". We then stretched our mind to find what it stood for. Lisp is a family of computer programming languages with a long history and a distinctive, fully parenthesized prefix notation.
If the third argument is missing or zero, the remainder of the string is returned. Record length is per-variable; multiple variables may be associated with the same unit, but with different record lengths. B The unit will be opened for binary access. On input newline characters have no special meaning; the number of bytes transferred deppends on record length see above. On output no newline is appended. A synonym for B,1. T Terminal mode. No newline characters are added on output, and any newline characters are returned on input. Terminal mode effects only the referenced unit.
Terminal mode is useful for outputting prompts in interactive programs. Q Quiet mode. Turns off input echo on terminals. Effects only input from this unit.
macro implementation of SNOBOL4 
U Update mode. The unit is opened for both input and output. W Unbuffered writes. A suffix of k multiplies the number by A larger dynamic region may result in fewer garbage collections storage regenerations , however large values may cause execution to slow down when large amounts of garbage collect. Most programs do not need an increased dynamic region to run. By default programs with compilation errors will not be run. Default listing side is LEFT. By default programs are run after compilation.
Any remaining strings are treated as files or user parameters. A -- terminates processing of arguments as files, and makes the remaining arguments available as user parameters see the HOST function. The pattern match stack is used to save backtracking and conditional assignment information. Griswold, J.
Poage, and I. Deprecate in favor of the newer and safer snobol4 port. Quiet that last niggling warning in the install process. It was never a problem, but often fooled pointyhat into thinking it was. Prodded-by: BugMagnet via pointyhat. Eliminate warnings from function prototype mismatches.
The Macro Implementation of Snobol 4: A Case Study of Machine-Independent Software Development
The snobol interpreter itself is chock full of pointer to int type punning and is likely to fail in hard-to-debug ways on non-VAX-like architectures. Add 'SIZE' to ports distinfo.
Prodded-by: trevor. Follow the bouncing C compiler: use stdargs instead of varargs in this lovely ancient code. Compile cleanly on GCC 3. Clear moonlight beckons.
Related Macroimplementation of Snobol 4
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