AskDefine | Define evaluate

Dictionary Definition

evaluate v : place a value on; judge the worth of something; "I will have the family jewels appraised by a professional" [syn: measure, valuate, assess, appraise, value]

User Contributed Dictionary

English

Etymology

From evaluation.

Verb

  1. to draw conclusions from by examining
    It will take several weeks to evaluate the material gathered in the survey.
  2. to compute an expression
    Evaluate this polynomial

Translations

to draw conclusions from by examining

Extensive Definition

In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language. While interpretation and compilation are the two principal means by which programming languages are implemented, these are not fully distinct categories, one of the reasons being that most interpreting systems also perform some translation work, just like compilers. An interpreter may be a program that either
  1. executes the source code directly
  2. translates source code into some efficient intermediate representation (code) and immediately executes this
  3. explicitly executes stored precompiled code made by a compiler which is part of the interpreter system
Perl, Python, MATLAB, and Ruby are examples of type 2, while UCSD Pascal and the Java virtual machine are type 3: Java source programs are compiled ahead of time and stored as machine independent code, which is then linked at run-time and executed by an interpreter (virtual machine). Some systems, such as Smalltalk, and others, may also combine 2 and 3.
The terms Interpreted language or Compiled language merely mean that the canonical implementation of that language is an interpreter or a compiler; a high level language is basically an abstraction which is (ideally) independent of particular implementations.

Efficiency

The main disadvantage of interpreters is that when a program is interpreted, it typically runs slower than if it had been compiled. The difference in speeds could be tiny or great; often an order of magnitude and sometimes more. It generally takes longer to run a program under an interpreter than to run the compiled code but it can take less time to interpret it than the total time required to compile and run it. This is especially important when prototyping and testing code when an edit-interpret-debug cycle can often be much shorter than an edit-compile-run-debug cycle.
Interpreting code is slower than running the compiled code because the interpreter must analyze each statement in the program each time it is executed and then perform the desired action, whereas the compiled code just performs the action within a fixed context determined by the compilation. This run-time analysis is known as "interpretive overhead". Access to variables is also slower in an interpreter because the mapping of identifiers to storage locations must be done repeatedly at run-time rather than at compile time.
There are various compromises between the development speed when using an interpreter and the execution speed when using a compiler. Some systems (e.g., some LISPs) allow interpreted and compiled code to call each other and to share variables. This means that once a routine has been tested and debugged under the interpreter it can be compiled and thus benefit from faster execution while other routines are being developed. Many interpreters do not execute the source code as it stands but convert it into some more compact internal form. For example, some BASIC interpreters replace keywords with single byte tokens which can be used to find the instruction in a jump table. An interpreter might well use the same lexical analyzer and parser as the compiler and then interpret the resulting abstract syntax tree.

Bytecode interpreters

There is a spectrum of possibilities between interpreting and compiling, depending on the amount of analysis performed before the program is executed. For example, Emacs Lisp is compiled to bytecode, which is a highly compressed and optimized representation of the Lisp source, but is not machine code (and therefore not tied to any particular hardware). This "compiled" code is then interpreted by a bytecode interpreter (itself written in C). The compiled code in this case is machine code for a virtual machine, which is implemented not in hardware, but in the bytecode interpreter. The same approach is used with the Forth code used in Open Firmware systems: the source language is compiled into "F code" (a bytecode), which is then interpreted by a virtual machine.

Abstract Syntax Tree interpreters

In the spectrum between interpreting and compiling, another approach is transforming the source code into an optimized Abstract Syntax Tree (AST), and then proceeding to execute the program following this tree structure. In this approach each sentence needs to be parsed just once. As and advantage over bytecode, the AST keeps the global program structure and relations between statements (which in a bytecode representation is lost), and provides a more compact representation.
Thus, AST has been proposed as a better intermediate format for Just-in-time compilers than bytecode. Also, it allows to perform better analysis during runtime. An AST-based Java interpreter has been proved to be faster than a similar bytecode-based interpreter, thanks to the more powerful optimizations allowed by having the complete structure of the program available during execution, and with higher abstraction.

Just-in-time compilation

Further blurring the distinction between interpreters, byte-code interpreters and compilation is just-in-time compilation (or JIT), a technique in which the intermediate representation is compiled to native machine code at runtime. This confers the efficiency of running native code, at the cost of startup time and increased memory use when the bytecode or AST is first compiled. Adaptive optimization is a complementary technique in which the interpreter profiles the running program and compiles its most frequently-executed parts into native code. Both techniques are a few decades old, appearing in languages such as Smalltalk in the 1980s.
Just-in-time compilation has gained mainstream attention amongst language implementors in recent years, with Java, Python and the .NET Framework all now including JITs.

Punched card interpreter

The term "interpreter" often referred to a piece of unit record equipment that could read punched cards and print the characters in human-readable form on the card. The IBM 550 Numeric Interpreter and IBM 557 Alphabetic Interpreter are typical examples from 1930 and 1954, respectively.

Foot notes

See also

External links

  • DrPubaGump A tiny Interpreter written in Scheme, which provides to interpret PUBA-GUMP (a subset of BASIC) in Scheme
  • IBM Card Interpreters page at Columbia University
evaluate in Arabic: مفسر (برمجة)
evaluate in Czech: Interpret (software)
evaluate in Danish: Fortolker
evaluate in German: Interpreter
evaluate in Estonian: Interpretaator
evaluate in Spanish: Intérprete (informática)
evaluate in French: Interprète (informatique)
evaluate in Korean: 인터프리터
evaluate in Croatian: Interpreter
evaluate in Icelandic: Túlkur (tölvunarfræði)
evaluate in Italian: Interprete (informatica)
evaluate in Hebrew: מפרש (תוכנה)
evaluate in Lithuanian: Interpretatorius
evaluate in Hungarian: Értelmező
evaluate in Dutch: Interpreter
evaluate in Japanese: インタプリタ
evaluate in Polish: Interpreter
evaluate in Portuguese: Interpretador
evaluate in Romanian: Interpretor
evaluate in Russian: Интерпретатор
evaluate in Simple English: Interpreter (computing)
evaluate in Slovak: Interpreter (programovanie)
evaluate in Serbian: Интерпретатор
evaluate in Finnish: Ohjelmointikielen tulkki
evaluate in Swedish: Interpretator
evaluate in Thai: โปรแกรมแปลคำสั่ง
evaluate in Vietnamese: Trình thông dịch
evaluate in Turkish: Yorumlayıcı
evaluate in Ukrainian: Інтерпретатор
evaluate in Chinese: 直譯器

Synonyms, Antonyms and Related Words

appraise, appreciate, approximate, ascertain, assay, assess, calculate, calibrate, caliper, call, catalog, categorize, check a parameter, class, classify, compute, criticize, determine, dial, divide, estimate, factor, fair-trade, fathom, figure, form an estimate, gauge, give an appreciation, grade, graduate, group, guess, identify, judge, make an estimation, mark, measure, mensurate, mete, meter, pace, plumb, price, prize, probe, quantify, quantize, quote a price, rank, rate, reckon, set at, sift, size, size up, sort, sort out, sound, span, step, survey, take a reading, thrash out, triangulate, valorize, valuate, value, weigh, winnow
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