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| In [[computer science]] a '''translation system''' is software capable of translating a text from one [[language]] to another. The most common example of a translation system is a compiler, which translates from one [[formal language]] to another, generally to translate from a human readable program description to a machine readable program description.
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| == Compilers ==
| | In [[computer science]], a '''translation system''' is a [[program]] which translates one [[language]] into another. If both the source and target language are [[formal language|formal languages]], which are fully specified so there can be no ambiguity, the program is called a [[compiler]]. But software which translates between two [[natural language|natural languages]] must use many more techniques and [[heuristics]] than a compiler, due to the inherent ambiguity of natural language. The endeavor of translating natural languages using a [[computer]] [[program]] involves both the academic disciplines of [[computer science]] and [[linguistics]]. |
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| As was mentioned earlier, a compiler is a program which can translate from one formal language into another. Generally, the source language is a high level, human readable language (such as [[Java]] or [[Ada]]), though it could be any unambiguous program representation, such as a [[flow chart]] or [[finite state machine]] description of an algorithm. The target language is generally [[machine language]], though it could just as well be another high level language or even a presentation language (such as [[HTML]]).
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| === Structure of Compilers ===
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| Like any class of software, there is a large variety of implementations. However, most compilers follow this pattern,
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| # [[lexical analysis|Lexical Analysis or Scanning]], in which the input characters are recognized by a set of [[regular expressions]] and output as a sequence of [[token|tokens]].
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| # [[syntactic analysis|Syntactical Analysis or Parsing]], in which the input tokens are recognized by a set of [[pushdown automatons]] and output a sequence of semantic actions.
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| # [[semantic analysis|Semantic Analysis]], in which each semantic action builds an internal or intermediate representation of the source program, and [[context sensitive]] errors (any error that cannot be discriminated by a [[context-free language]]) are detected.
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| # [[optimization (computer science)|Optimization]], in which the compiler attempts to replace computationally expensive portions of the program with less expensive versions, provided that no substitution affects the operation of the program.
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| # [[code generation|Code Generation]], in which the intermediate language is translated piece at a time to the target language.
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| # [[peephole optimizations|Peephole Optimization]], a final optimization pass in which analyses the output code over a small region (the peephole), searching for very localized optimizations.
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| In actuality, there may be multiple optimization stages scattered throughout this process. Additionally, most modern compilers repeatedly translate the language from an intermediate representation to a simpler intermediate representation in order to accomodate a wide swath of optimizations that operate on different levels of detail.
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| ==== Lexical Analysis ====
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| During lexical analysis, a set of regular expressions translate the input sequence (generally characters) into an output sequence (called tokens). One popular tool to simplify the creation of lexical analyzers is a software package called [[lex]].
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| Readers accustomed to programming may benefit from a few examples of errors that can be detected during this phase. A lexical analyzer could detect errors in a single token, for instance a number that has the letter 'y' in it, or a string with a missing end quote.
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| ==== Syntactic Analysis ====
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| During syntactic analysis, an input sequence of tokens is matched against a set of gramatical constructs called [[productions]]. As each production is matched, a semantic action routine is called. The role of each semantic action is to build an intermediate representation of the input program, such as a list of variables and functions, and a sequence of instructions comprising each function.
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| Readers accustomed to programming may benefit from a few examples of errors that can be detected during this phase. A Syntactic analyzer could detect a syntactic error, such as a missing semicolon or curly brace. A syntactic analyzer cannot detect the use of an undeclared variable. This is because the declaration of a variable before its use is a [[context sensitive]] langauge requirement, though syntactic analyzers are generally [[context-free]] language recognizers.
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| ==== Semantic Analysis ====
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| During semantic analysis, a compiler builds and examines an intermediate representation of the source program and checks it for consistency.
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| Readers accustomed to programming may benefit from a few examples of errors that can be detected during this phase. A semantic analyzer could detect errors, such as undeclared variables or functions.
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| ==== Optimization ====
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| During optimization, a compiler attempts to alter its internal representation of the input program as to improve code speed, size, or many other code characteristics.
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| ==== Code Generation ====
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| ==== Peephole Optimization ====
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| == Translation Systems other than Compilers ==
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| Babelfish?
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| == See Also ==
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| * [[formal language]]
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| * [[high-level language]]
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| * [[lexical analysis|Lexical Analysis or Scanning]]
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| * [[syntactic analysis|Syntactical Analysis or Parsing]]
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| * [[semantic analysis|Semantic Analysis]]
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| * [[optimization (computer science)|Optimization]]
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| * [[code generation|Code Generation]]
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