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nsist of 3 numbers an opcode that selects the add operation and two memory locations the programs in decimal or binary form were read in from punched cards paper tape magnetic tape or toggled in on switches on the front panel of the computer machine languages were later termed first generation programming languages 1gl the next step was the development of the so called second generation programming languages 2gl or assembly languages which were still closely tied to the instruction set architecture of the specific computer these served to make the program much more human readable and relieved the programmer of tedious and error prone address calculations the first high level programming languages or third generation programming languages 3gl were written in the 1950s an early high level programming language to be designed for a computer was plankalkül developed for the german z3 by konrad zuse between 1943 and 1945 however it was not implemented until 1998 and 2000 22 john mauchly s short code proposed in 1949 was one of the first high level languages ever developed for an electronic computer 23 unlike machine code short code statements represented mathematical expressions in understandable form however the program had to be translated into machine code every time it ran making the process much slower than running the equivalent machine code at the university of manchester alick glennie developed autocode in the early 1950s as a programming language it used a compiler to automatically convert the language into machine code the first code and compiler was developed in 1952 for the mark 1 computer at the university of manchester and is considered to be the first compiled high level programming language 24 25 the second autocode was developed for the mark 1 by r a brooker in 1954 and was called the mark 1 autocode brooker also developed an autocode for the ferranti mercury in the 1950s in conjunction with the university of manchester the version for the edsac 2 was devised by d f hartley of university of cambridge mathematical laboratory in 1961 known as edsac 2 autocode it was a straight development from mercury autocode adapted for local circumstances and was noted for its object code optimisation and source language diagnostics which were advanced for the time a contemporary but separate thread of development atlas autocode was developed for the university of manchester atlas 1 machine in 1954 fortran was invented at ibm by john backus it was the first widely used high level general purpose programming language to have a functional implementation as opposed to just a design on paper 26 27 it is still a popular language for high performance computing 28 and is used for programs that benchmark and rank the world s fastest supercomputers 29 another early programming language was devised by grace hopper in the us called flow matic it was developed for the univac i at remington rand during the period from 1955 until 1959 hopper found that business data processing customers were uncomfortable with mathematical notation and in early 1955 she and her team wrote a specification for an english programming language and implemented a prototype 30 the flow matic compiler became publicly available in early 1958 and was substantially complete in 1959 31 flow matic was a major influence in the design of cobol since only it and its direct descendant aimaco were in actual use at the time 32 refinement edit the increased use of high level languages introduced a requirement for low level programming languages or system programming languages these languages to varying degrees provide facilities between assembly languages and high level languages they can be used to perform tasks that require direct access to hardware facilities but still provide higher level control structures and error checking the period from the 1960s to the late 1970s brought the development of the major language paradigms now in use apl introduced array programming and influenced functional programming 33 algol refined both structured procedural programming and the discipline of language specification the revised report on the algorithmic language algol 60 became a model for how later language specifications were written lisp implemented in 1958 was the first dynamically typed functional programming language in the 1960s simula was the first language designed to support object oriented programming in the mid 1970s smalltalk followed with the first purely object oriented language c was developed between 1969 and 1973 as a system programming language for the unix operating system and remains popular 34 prolog designed in 1972 was the first logic programming language in 1978 ml built a polymorphic type system on top of lisp pioneering statically typed functional programming languages each of these languages spawned descendants and most modern programming languages count at least one of them in their ancestry the 1960s and 1970s also saw considerable debate over the merits of structured programming and whether programming languages should be designed to support it 35 edsger dijkstra in a famous 1968 letter published in the communications of the acm argued that goto statements should be eliminated from all higher level programming languages 36 consolidation and growth edit a small selection of programming language textbooks the 1980s were years of relative consolidation c combined object oriented and systems programming the united states government standardized ada a systems programming language derived from pascal and intended for use by defense contractors in japan and elsewhere vast sums were spent investigating the so called fifth generation languages that incorporated logic programming constructs 37 the functional languages community moved to standardize ml and lisp rather than inventing new paradigms all of these movements elaborated upon the ideas invented in the previous decades one important trend in language design for programming large scale systems during the 1980s was an increased focus on the use of modules or large scale organizational units of code modula 2 ada and ml all developed notable module systems in the 1980s which were often wedded to generic programming constructs 38 the rapid growth of the internet in the mid 1990s created opportunities for new languages perl originally a unix scripting tool first released in 1987 became common in dynamic websites java came to be used for server side programming and bytecode virtual machines became popular again in commercial settings with their promise of write once run anywhere ucsd pascal had been popular for a time in the early 1980s these developments were not fundamentally novel rather they were refinements of many existing languages and paradigms although their syntax was often based on the c family of programming languages programming language evolution continues in both industry and research current directions include security and reliability verification new kinds of modularity mixins delegates aspects and database integration such as microsoft s linq fourth generation programming languages 4gl are computer programming languages that aim to provide a higher level of abstraction of the internal computer hardware details than 3gls fifth generation programming languages 5gl are programming languages based on solving problems using constraints given to the program rather than using an algorithm written by a programmer elements edit all programming languages have some primitive building blocks for the description of data and the processes or transformations applied to them like the addition of two numbers or the selection of an item from a collection these primitives are defined by syntactic and semantic rules which describe their structure and meaning respectively syntax edit main article syntax programming languages parse tree of python code with inset tokenization syntax highlighting is often used to aid programmers in recognizing elements of source code the language above is python a programming language s surface form is known as its syntax most programming languages are purely textual they use sequences of text including words numbers and punctuation much like written natural languages on the other hand there are some programming languages which are more graphical in nature using visual relationships between symbols to specify a program the syntax of a language describes the possible combinations of symbols that form a syntactically correct program the meaning given to a combination of symbols is handled by semantics either formal or hard coded in a reference implementation since most languages are textual this article discusses textual syntax programming language syntax is usually defined using a combination of regular expressions for lexical structure and backus naur form for grammatical structure below is a simple grammar based on lisp expression atom list atom number symbol number 0 9 symbol a z a z list expression this grammar specifies the following an expression is either an atom or a list an atom is either a number or a symbol a number is an unbroken sequence of one or more decimal digits optionally preceded by a plus or minus sign a symbol is a letter followed by zero or more of any characters excluding whitespace and a list is a matched pair of parentheses with zero or more expressions inside it the following are examples of well formed token sequences in this grammar 12345 and a b c232 1 not all syntactically correct programs are semantically correct many syntactically correct programs are nonetheless ill formed per the language s rules and may depending on the language specification and the soundness of the implementation result in an error on translation or execution in some cases such programs may exhibit undefined behavior even when a program is well defined within a language it may still have a meaning that is not intended by the person who wrote it using natural language as an example it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false colorless green ideas sleep furiously is grammatically well formed but has no generally accepted meaning john is a married bachelor is grammatically well formed but expresses a meaning that cannot be true the following c language fragment is syntactically correct but performs operations that are not semantically defined the operation p 4 has no meaning for a value having a complex type and p im is not defined because the value of p is the null pointer complex p null complex abs_p sqrt p 4 p im if the type declaration on the first line were omitted the program would trigger an error on undefined variable p during compilation however the program would still be syntactically correct since type declarations provide only semantic information the grammar needed to specify a programming language can be classified by its position in the chomsky hierarchy the syntax of most programming languages can be specified using a type 2 grammar i e they are context free grammars 39 some languages including perl and lisp contain constructs that allow execution during the parsing phase languages that have constructs that allow the programmer to alter the behavior of the parser make syntax analysis an undecidable problem and generally blur the distinction between parsing and execution 40 in contrast to lisp s macro system and perl s begin blocks which may contain general computations c macros are merely string replacements and do not require code execution 41 semantics edit the term semantics refers to the meaning of languages as opposed to their form syntax static semantics edit the static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms 1 for compiled languages static semantics essentially include those semantic rules that can be checked at compile time examples include checking that every identifier is declared before it is used in languages that require such declarations or that the labels on the arms of a case statement are distinct 42 many important restrictions of this type like checking that identifiers are used in the appropriate context e g not adding an integer to a function name or that subroutine calls have the appropriate number and type of arguments can be enforced by defining them as rules in a logic called a type system other forms of static analyses like data flow analysis may also be part of static semantics newer programming languages like java and c have definite assignment analysis a form of data flow analysis as part of their static semantics dynamic semantics edit main article semantics of programming languages once data has been specified the machine must be instructed to perform operations on the data for example the semantics may define the strategy by which expressions are evaluated to values or the manner in which control structures conditionally execute statements the dynamic semantics also known as execution semantics of a language defines how and when the various constructs of a language should produce a program behavior there are many ways of defining execution semantics natural language is often used to specify the execution semantics of languages commonly used in practice a significant amount of academic research went into formal semantics of programming languages which allow execution semantics to be specified in a formal manner results from this field of research have seen limited application to programming language design and implementation outside academia type system edit main articles data type type system and type safety a type system defines how a programming language classifies values and expressions into types how it can manipulate those types and how they interact the goal of a type system is to verify and usually enforce a certain level of correctness in programs written in that language by detecting certain incorrect operations any decidable type system involves a trade off while it rejects many incorrect programs it can also prohibit some correct albeit unusual programs in order to bypass this downside a number of languages have type loopholes usually unchecked casts that may be used by the programmer to explicitly allow a normally disallowed operation between different types in most typed languages the type system is used only to type check programs but a number of languages usually functional ones infer types relieving the programmer from the need to write type annotations the formal design and study of type systems is known as type theory typed versus untyped languages edit a language is typed if the specification of every operation defines types of data to which the operation is applicable 43 for example the data represented by this text between the quotes is a string and in many programming languages dividing a number by a string has no meaning and will not be executed the in...