Compiled vs Interpreted Languages

Question

I m trying to get a better understanding of the difference  I ve found a lot of explanations online  but they tend towards the abstract differences rather than the practical implications   Most of my programming experiences has been with CPython  dynamic  interpreted   and Java  static  compiled   However  I understand that there are other kinds of interpreted and compiled languages  Aside from the fact that executable files can be distributed from programs written in compiled languages  are there any advantages disadvantages to each type  Oftentimes  I hear people arguing that interpreted languages can be used interactively  but I believe that compiled languages can have interactive implementations as well  correct

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A compiled language is one where the program, once compiled, is expressed in the instructions of the target machine. For example, an addition "+" operation in your source code could be translated directly to the "ADD" instruction in machine code.

An interpreted language is one where the instructions are not directly executed by the target machine, but instead read and executed by some other program (which normally is written in the language of the native machine). For example, the same "+" operation would be recognised by the interpreter at run time, which would then call its own "add(a,b)" function with the appropriate arguments, which would then execute the machine code "ADD" instruction.

You can do anything that you can do in an interpreted language in a compiled language and vice-versa - they are both Turing complete. Both however have advantages and disadvantages for implementation and use.

I'm going to completely generalise (purists forgive me!) but, roughly, here are the advantages of compiled languages:

Faster performance by directly using the native code of the target machine
Opportunity to apply quite powerful optimisations during the compile stage

And here are the advantages of interpreted languages:

Easier to implement (writing good compilers is very hard!!)
No need to run a compilation stage: can execute code directly "on the fly"
Can be more convenient for dynamic languages

Note that modern techniques such as bytecode compilation add some extra complexity - what happens here is that the compiler targets a "virtual machine" which is not the same as the underlying hardware. These virtual machine instructions can then be compiled again at a later stage to get native code (e.g. as done by the Java JVM JIT compiler).

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A compiler and an interpreter do the same job  translating a programming language to another pgoramming language  usually closer to the hardware  often direct executable machine code   Traditionally   compiled  means that this translation happens all in one go  is done by a developer  and the resulting executable is distributed to users  Pure example  C    Compilation usually takes pretty long and tries to do lots of expensive optmization so that the resulting executable runs faster  End users don t have the tools and knowledge to compile stuff themselves  and the executable often has to run on a variety of hardware  so you can t do many hardware-specific optimizations  During development  the separate compilation step means a longer feedback cycle   Traditionally   interpreted  means that the translation happens  on the fly   when the user wants to run the program  Pure example  vanilla PHP  A naive interpreter has to parse and translate every piece of code every time it runs  which makes it very slow  It can t do complex  costly optimizations because they d take longer than the time saved in execution  But it can fully use the capabilities of the hardware it runs on  The lack of a separrate compilation step reduces feedback time during development   But nowadays  compiled vs  interpreted  is not a black-or-white issue  there are shades in between  Naive  simple interpreters are pretty much extinct  Many languages use a two-step process where the high-level code is translated to a platform-independant bytecode  which is much faster to interpret   Then you have  just in time compilers  which compile code at most once per program run  sometimes cache results  and even intelligently decide to interpret code that s run rarely  and do powerful optimizations for code that runs a lot  During development  debuggers are capable of switching code inside a running program even for traditionally compiled languages

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From http   www quora com What-is-the-difference-between-compiled-and-interpreted-programming-languages     There is no difference  because    compiled programming language    and      interpreted programming language    aren   t meaningful concepts  Any   programming language  and I really mean any  can be interpreted or   compiled  Thus  interpretation and compilation are implementation   techniques  not attributes of languages       Interpretation is a technique whereby another program  the   interpreter  performs operations on behalf of the program being   interpreted in order to run it  If you can imagine reading a program   and doing what it says to do step-by-step  say on a piece of scratch   paper  that   s just what an interpreter does as well  A common reason   to interpret a program is that interpreters are relatively easy to   write  Another reason is that an interpreter can monitor what a   program tries to do as it runs  to enforce a policy  say  for   security       Compilation is a technique whereby a program written in one language    the    source language     is translated into a program in another   language  the    object language      which hopefully means the same thing   as the original program  While doing the translation  it is common for   the compiler to also try to transform the program in ways that will   make the object program faster  without changing its meaning    A   common reason to compile a program is that there   s some good way to   run programs in the object language quickly and without the overhead   of interpreting the source language along the way       You may have guessed  based on the above definitions  that these two   implementation techniques are not mutually exclusive  and may even be   complementary  Traditionally  the object language of a compiler was   machine code or something similar  which refers to any number of   programming languages understood by particular computer CPUs  The   machine code would then run    on the metal     though one might see  if   one looks closely enough  that the    metal    works a lot like an   interpreter   Today  however  it   s very common to use a compiler to   generate object code that is meant to be interpreted   for example  this   is how Java used to  and sometimes still does  work  There are   compilers that translate other languages to JavaScript  which is then   often run in a web browser  which might interpret the JavaScript  or   compile it a virtual machine or native code  We also have interpreters   for machine code  which can be used to emulate one kind of hardware on   another  Or  one might use a compiler to generate object code that is   then the source code for another compiler  which might even compile   code in memory just in time for it to run  which in turn       you get   the idea  There are many ways to combine these concepts

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Compile is the process of creating an executable program from code written in a compiled programming language  Compiling allows the computer to run and understand the program without the need of the programming software used to create it  When a program is compiled it is often compiled for a specific platform  e g  IBM platform  that works with IBM compatible computers  but not other platforms  e g  Apple platform   The first compiler was developed by Grace Hopper while working on the Harvard Mark I computer  Today  most high-level languages will include their own compiler or have toolkits available that can be used to compile the program  A good example of a compiler used with Java is Eclipse and an example of a compiler used with C and C   is the gcc command  Depending on how big the program is it should take a few seconds or minutes to compile and if no errors are encountered while being compiled an executable file is created check this information

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It s rather difficult to give a practical answer because the difference is about the language definition itself  It s possible to build an interpreter for every compiled language  but it s not possible to build an compiler for every interpreted language  It s very much about the formal definition of a language  So that theoretical informatics stuff noboby likes at university

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First  a clarification  Java is not fully static-compiled and linked in the way C    It is compiled into bytecode  which is then interpreted by a JVM  The JVM can go and do just-in-time compilation to the native machine language  but doesn t have to do it  More to the point  I think interactivity is the main practical difference  Since everything is interpreted  you can take a small excerpt of code  parse and run it against the current state of the environment  Thus  if you had already executed code that initialized a variable  you would have access to that variable  etc  It really lends itself way to things like the functional style  Interpretation  however  costs a lot  especially when you have a large system with a lot of references and context  By definition  it is wasteful because identical code may have to be interpreted and optimized twice  although most runtimes have some caching and optimizations for that   Still  you pay a runtime cost and often need a runtime environment  You are also less likely to see complex interprocedural optimizations because at present their performance is not sufficiently interactive  Therefore  for large systems that are not going to change much  and for certain languages  it makes more sense to precompile and prelink everything  do all the optimizations that you can do  This ends up with a very lean runtime that is already optimized for the target machine  As for generating executables  that has little to do with it  IMHO  You can often create an executable from a compiled language  But you can also create an executable from an interpreted language  except that the interpreter and runtime is already packaged in the exectuable and hidden from you  This means that you generally still pay the runtime costs  although I am sure that for some language there are ways to translate everything to a tree executable   I disagree that all languages could be made interactive  Certain languages  like C  are so tied to the machine and the entire link structure that I m not sure you can build a meaningful fully-fledged interactive version

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A language itself is neither compiled nor interpreted  only a specific implementation of a language is   Java is a perfect example   There is a bytecode-based platform  the JVM   a native compiler  gcj  and an interpeter for a superset of Java  bsh    So what is Java now  Bytecode-compiled  native-compiled or interpreted     Other languages  which are compiled as well as interpreted  are Scala  Haskell or Ocaml   Each of these languages has an interactive interpreter  as well as a compiler to byte-code or native machine code   So generally categorizing languages by  compiled  and  interpreted  doesn t make much sense

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Start thinking in terms of a  blast from the past   Once upon a time  long long ago  there lived in the land of computing interpreters and compilers  All kinds of fuss ensued over the merits of one over the other  The general opinion at that time was something along the lines of    Interpreter  Fast to develop  edit and run   Slow to execute because each statement had to be interpreted into machine code every time it was executed  think of what this meant for a loop executed thousands of times   Compiler  Slow to develop  edit  compile  link and run  The compile link steps could take serious time   Fast to execute  The whole program was already in native machine code    A one or two order of magnitude difference in the runtime performance existed between an interpreted program and a compiled program  Other distinguishing  points  run-time mutability of the code for example  were also of some interest but the major distinction revolved around the run-time performance issues   Today the landscape has evolved to such an extent that the compiled interpreted distinction is  pretty much irrelevant  Many compiled languages call upon run-time services that are not completely machine code based  Also  most interpreted languages are  compiled  into byte-code before execution  Byte-code interpreters can be very efficient and rival some compiler generated code from an execution speed point of view   The classic difference is that compilers generated native machine code  interpreters read source code and generated machine code on the fly using some sort of run-time system   Today there are very few classic interpreters left - almost all of them compile into byte-code  or some other semi-compiled state  which then runs on a virtual  machine

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Short  un-precise  definition   Compiled language  Entire program is translated to machine code at once  then the machine code is run by the CPU   Interpreted language  Program is read line-by-line and as soon as a line is read the machine instructions for that line are executed by the CPU   But really  few languages these days are purely compiled or purely interpreted  it often is a mix  For a more detailed description with pictures  see this thread   What is the difference between compilation and interpretation   Or my later blog post   https   orangejuiceliberationfront com the-difference-between-compiler-and-interpreter

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The extreme and simple cases    A compiler will produce a binary executable in the target machine s native executable format  This binary file contains all required resources except for system libraries  it s ready to run with no further preparation and processing and it runs like lightning because the code is the native code for the CPU on the target machine  An interpreter will present the user with a prompt in a loop where he can enter statements or code  and upon hitting RUN or the equivalent the interpreter will examine  scan  parse and interpretatively execute each line until the program runs to a stopping point or an error  Because each line is treated on its own and the interpreter doesn t  learn  anything from having seen the line before  the effort of converting human-readable language to machine instructions is incurred every time for every line  so it s dog slow  On the bright side  the user can inspect and otherwise interact with his program in all kinds of ways  Changing variables  changing code  running in trace or debug modes    whatever    With those out of the way  let me explain that life ain t so simple any more  For instance     Many interpreters will pre-compile the code they re given so the translation step doesn t have to be repeated again and again   Some compilers compile not to CPU-specific machine instructions but to bytecode  a kind of artificial machine code for a ficticious machine  This makes the compiled program a bit more portable  but requires a bytecode interpreter on every target system  The bytecode interpreters  I m looking at Java here  recently tend to re-compile the bytecode they get for the CPU of the target section just before execution  called JIT   To save time  this is often only done for code that runs often  hotspots   Some systems that look and act like interpreters  Clojure  for instance  compile any code they get  immediately  but allow interactive access to the program s environment  That s basically the convenience of interpreters with the speed of binary compilation  Some compilers don t really compile  they just pre-digest and compress code  I heard a while back that s how Perl works  So sometimes the compiler is just doing a bit of the work and most of it is still interpretation    In the end  these days  interpreting vs  compiling is a trade-off  with time spent  once  compiling often being rewarded by better runtime performance  but an interpretative environment giving more opportunities for interaction  Compiling vs  interpreting is mostly a matter of how the work of  understanding  the program is divided up between different processes  and the line is a bit blurry these days as languages and products try to offer the best of both worlds

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The biggest advantage of interpreted source code over compiled source code is PORTABILITY   If your source code is compiled  you need to compile a different executable for each type of processor and or platform that you want your program to run on  e g  one for Windows x86  one for Windows x64  one for Linux x64  and so on   Furthermore  unless your code is completely standards compliant and does not use any platform-specific functions libraries  you will actually need to write and maintain multiple code bases   If your source code is interpreted  you only need to write it once and it can be interpreted and executed by an appropriate interpreter on any platform  It s portable  Note that an interpreter itself is an executable program that is written and compiled for a specific platform   An advantage of compiled code is that it hides the source code from the end user  which might be intellectual property  because instead of deploying the original human-readable source code  you deploy an obscure binary executable file

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The Python Book    2015 Imagine Publishing Ltd  simply distunguishes the difference by the following hint mentioned in page 10 as      An interpreted language such as Python is one where the source code is converted to machine code and then executed each time the program runs  This is different from a compiled language such as C  where the source code is only converted to machine code once     the resulting machine code is then executed each time the program runs

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