What is the difference between procedural programming and functional programming

Question

I ve read the Wikipedia articles for both procedural programming and functional programming  but I m still slightly confused  Could someone boil it down to the core

User · Answer

If you have a chance  I would recommand getting a copy of Lisp Scheme  and doing some projects in it  Most of the ideas that have lately become bandwagons were expressed in Lisp decades ago  functional programming  continuations  as closures   garbage collection  even XML   So that would be a good way to get a head start on all these current ideas  and a few more besides  like symbolic computation   You should know what functional programming is good for  and what it isn t good for  It isn t good for everything  Some problems are best expressed in terms of side-effects  where the same question gives differet answers depending on when it is asked

User · Answer

Procedural programming divides sequences of statements and conditional constructs into separate blocks called procedures that are parameterized over arguments that are  non-functional  values   Functional programming is the same except that functions are first-class values  so they can be passed as arguments to other functions and returned as results from function calls   Note that functional programming is a generalization of procedural programming in this interpretation  However  a minority interpret  functional programming  to mean side-effect-free which is quite different but irrelevant for all major functional languages except Haskell

User · Answer

Basically the two styles  are like Yin and Yang  One is organized  while the other chaotic  There are situations when Functional programming is the obvious choice  and other situations were Procedural programming is the better choice  This is why there are at least two languages that have recently come out with a new version  that embraces both programming styles    Perl  6 and D  2    Procedural    The output of a routine does not always have a direct correlation with the input  Everything is done in a specific order  Execution of a routine may have side effects  Tends to emphasize implementing solutions in a linear fashion     Perl 6      sub factorial   UInt D  n is copy   returns UInt        modify  quot outside quot  state   state  call-count        in this case it is rather pointless as     it can t even be accessed from outside    my  result   1     loop      n  gt  0    n--          result     n          return  result       D 2   int factorial  int n       int result   1     for    n  gt  0   n--        result    n         return result       Functional    Often recursive  Always returns the same output for a given input  Order of evaluation is usually undefined  Must be stateless  i e  No operation can have side effects  Good fit for parallel execution Tends to emphasize a divide and conquer approach  May have the feature of Lazy Evaluation     Haskell     copied from Wikipedia    fac    Integer - gt  Integer  fac 0   1 fac n   n  gt  0   n   fac  n-1   or in one line  fac n   if n  gt  0 then n   fac  n-1  else 1    Perl 6      proto sub factorial   UInt D  n   returns UInt      multi sub factorial    0     1   multi sub factorial    n      n   samewith  n-1        n   factorial  n-1      D 2   pure int factorial  invariant int n      if  n  lt   1        return 1     else      return n   factorial  n-1             Side note   Factorial is actually a common example to show how easy it is to create new operators in Perl 6 the same way you would create a subroutine  This feature is so ingrained into Perl 6 that most operators in the Rakudo implementation are defined this way  It also allows you to add your own multi candidates to existing operators  sub postfix  lt     gt    UInt D  n -- gt  UInt     is tighter  amp infix  lt   gt           2     n    say 5     120   This example also shows range creation  2   n  and the list reduction meta-operator     OPERATOR     LIST  combined with the numeric infix multiplication operator      It also shows that you can put -- gt   UInt in the signature instead of returns  UInt after it    You can get away with starting the range with 2 as the multiply  quot operator quot  will return 1 when called without any arguments

User · Answer

None of the answers here show idiomatic functional programming  The recursive factorial answer is great for representing recursion in FP  but the majority of code is not recursive so I don t think that answer is fully representative   Say you have an arrays of strings  and each string represents an integer like  5  or  -200   You want to check this input array of strings against your internal test case  Using integer comparison   Both solutions are shown below  Procedural  arr equal a    Int   b    Str   - gt  Bool       if a len    b len            return false             bool ret   true      for  int i   0  i  lt  a len    Optimized with  amp  amp  ret    i               int a int   a i           int b int   parseInt b i            ret  amp   a int    b int              return ret      Functional  eq   i  j   gt  i    j   This is usually a built-in toInt   i   gt  parseInt i    Of course  parseInt     toInt here  but this is for visualization  arr equal a    Int   b    Str   - gt  Bool       zip a  b map toInt     Combines into  Int  Int      map eq      reduce true   i  j    gt  i  amp  amp  j    Start with true  and continuously  amp  amp  it with each value   While pure functional languages are generally research languages  As the real-world likes free side-effects   real-world procedural languages will use the much simpler functional syntax when appropriate   This is usually implemented with an external library like Lodash  or available built-in with newer languages like Rust  The heavy lifting of functional programming is done with functions concepts like map  filter  reduce  currying  partial  the last three of which you can look up for further understanding   Addendum  In order to be used in the wild  the compiler will normally have to work out how to convert the functional version into the procedural version internally  as function call overhead is too high  Recursive cases such as the factorial shown will use tricks such as tail call to remove O n  memory usage  The fact that there are no side effects allows functional compilers to implement the  amp  amp  ret optimization even when the  reduce is done last  Using Lodash in JS  obviously does not allow for any optimization  so it is a hit to performance  Which isn t usually a concern with web development   Languages like Rust will optimize internally  And have functions such as try fold to assist  amp  amp  ret optimization

User · Answer

Funtional Programming num   1  def function to add one num       num    1     return num   function to add one num  function to add one num  function to add one num  function to add one num  function to add one num    Final Output  2  Procedural Programming num   1  def procedure to add one        global num     num    1     return num   procedure to add one   procedure to add one   procedure to add one   procedure to add one   procedure to add one     Final Output  6  function to add one is a function procedure to add one is a procedure Even if you run the function five times  every time it will return 2 If you run the procedure five times  at the end of fifth run it will give you 6  DISCLAIMER  Obviously this is a hyper-simplified view of reality  This answer just gives a taste of  quot functions quot  as opposed to  quot procedures quot   Nothing more  Once you have tasted this superficial yet deeply penetrative intuition  start exploring the two paradigms  and you will start to see the difference quite clearly  Helps my students  hope it helps you too

User · Answer

In computer science  functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data  It emphasizes the application of functions  in contrast with the procedural programming style that emphasizes changes in state

User · Answer

Creighton   In Haskell there is a library function called product   prouduct list   foldr 1     list   or simply   product   foldr 1       so the  idiomatic  factorial  fac n   foldr 1       1  n    would simply be  fac n   product  1  n

User · Answer

Procedural languages tend to keep track of state  using variables  and tend to execute as a sequence of steps  Purely functional languages don t keep track of state  use immutable values  and tend to execute as a series of dependencies  In many cases the status of the call stack will hold the information that would be equivalent to that which would be stored in state variables in procedural code   Recursion is a classic example of functional style programming

User · Answer

Konrad said      As a consequence  a purely functional program always yields the same value for an input        and the order of evaluation is not well-defined  which means that uncertain values like       user input or random values are hard to model in purely functional languages    The order of evaluation in a purely functional program may be hard er  to reason about  especially with laziness  or even unimportant but I think that saying it is not well defined makes it sound like you can t tell if your program is going to work at all   Perhaps a better explanation would be that control flow in functional programs is based on when the value of a function s arguments are needed  The Good Thing about this that in well written programs  state becomes explicit  each function lists its inputs as parameters instead of arbitrarily munging global state  So on some level  it is easier to reason about order of evaluation with respect to one function at a time  Each function can ignore the rest of the universe and focus on what it needs to do  When combined  functions are guaranteed to work the same 1  as they would in isolation          uncertain values like user input or random values are hard to model in purely      functional languages    The solution to the input problem in purely functional programs is to embed an imperative language as a DSL using a sufficiently powerful abstraction  In imperative  or non-pure functional  languages this is not needed because you can  cheat  and pass state implicitly and order of evaluation is explicit  whether you like it or not   Because of this  cheating  and forced evaluation of all parameters to every function  in imperative languages 1  you lose the ability to create your own control flow mechanisms  without macros   2  code isn t inherently thread safe and or parallelizable by default  3  and implementing something like undo  time travel  takes careful work  imperative programmer must store a recipe for getting the old value s  back    whereas pure functional programming buys you all these things mdash and a few more I may have forgotten mdash  for free    I hope this doesn t sound like zealotry  I just wanted to add some perspective  Imperative programming and especially mixed paradigm programming in powerful languages like C  3 0 are  still totally effective ways to get things done and there is no silver bullet    1      except possibly  with respect memory usage  cf  foldl and foldl  in Haskell

User · Answer

One thing I hadn t seen really emphasized here is that modern functional languages such as Haskell really more on first class functions for flow control than explicit recursion   You don t need to define factorial recursively in Haskell  as was done above   I think something like   fac n   foldr     1  1  n    is a perfectly idiomatic construction  and much closer in spirit to using a loop than to using explicit recursion

User · Answer

To expand on Konrad s comment      As a consequence  a purely functional program always yields the same value for an input  and the order of evaluation is not well-defined    Because of this  functional code is generally easier to parallelize   Since there are  generally  no side effects of the functions  and they  generally  just act on their arguments  a lot of concurrency issues go away   Functional programming is also used when you need to be capable of proving your code is correct   This is much harder to do with procedural programming  not easy with functional  but still easier    Disclaimer   I haven t used functional programming in years  and only recently started looking at it again  so I might not be completely correct here

User · Answer

I believe that procedural functional objective programming are about how to approach a problem    The first style would plan everything in to steps  and solves the problem by implementing one step  a procedure  at a time  On the other hand  functional programming would emphasize the divide-and-conquer approach  where the problem is divided into sub-problem  then each sub-problem is solved  creating a function to solve that sub problem  and the results are combined to create the answer for the whole problem  Lastly  Objective programming would mimic the real world by create a mini-world inside the computer with many objects  each of which has a  somewhat  unique characteristics  and interacts with others  From those interactions the result would emerge   Each style of programming has its own advantages and weaknesses  Hence  doing something such as  pure programming   i e  purely procedural - no one does this  by the way  which is kind of weird - or purely functional or purely objective  is very difficult  if not impossible  except some elementary problems specially designed to demonstrate the advantage of a programming style  hence  we call those who like pureness  weenie   D    Then  from those styles  we have programming languages that is designed to optimized for some each style  For example  Assembly is all about procedural  Okay  most early languages are procedural  not only Asm  like C  Pascal   and Fortran  I heard   Then  we have all famous Java in objective school  Actually  Java and C  is also in a class called  money-oriented   but that is subject for another discussion   Also objective is Smalltalk  In functional school  we would have  nearly functional   some considered them to be impure  Lisp family and  ML family and many  purely functional  Haskell  Erlang  etc  By the way  there are many general languages such as Perl  Python  Ruby

User · Answer

To expand on Konrad s comment      and the order of evaluation is not   well-defined   Some functional languages have what is called Lazy Evaluation   Which means a function is not executed until the value is needed   Until that time the function itself is what is passed around   Procedural languages are step 1 step 2 step 3    if in step 2 you say add 2   2  it does it right then   In lazy evaluation you would say add 2   2  but if the result is never used  it never does the addition

User · Answer

A functional language  ideally  allows you to write a mathematical function  i e  a function that takes n arguments and returns a value  If the program is executed  this function is logically evaluated as needed 1  A procedural language  on the other hand  performs a series of sequential steps   There s a way of transforming sequential logic into functional logic called continuation passing style    As a consequence  a purely functional program always yields the same value for an input  and the order of evaluation is not well-defined  which means that uncertain values like user input or random values are hard to model in purely functional languages     1 As everything else in this answer  that   s a generalisation  This property  evaluating a computation when its result is needed rather than sequentially where it   s called  is known as    laziness     Not all functional languages are actually universally lazy  nor is laziness restricted to functional programming  Rather  the description given here provides a    mental framework    to think about different programming styles that are not distinct and opposite categories but rather fluid ideas

User · Answer

I ve never seen this definition given elsewhere  but I think this sums up the differences given here fairly well   Functional programming focuses on expressions  Procedural programming focuses on statements  Expressions have values  A functional program is an expression who s value is a sequence of instructions for the computer to carry out   Statements don t have values and instead modify the state of some conceptual machine   In a purely functional language there would be no statements  in the sense that there s no way to manipulate state  they might still have a syntactic construct named  statement   but unless it manipulates state I wouldn t call it a statement in this sense   In a purely procedural language there would be no expressions  everything would be an instruction which manipulates the state of the machine   Haskell would be an example of a purely functional language because there is no way to manipulate state  Machine code would be an example of a purely procedural language because everything in a program is a statement which manipulates the state of the registers and memory of the machine   The confusing part is that the vast majority of programming languages contain both expressions and statements  allowing you to mix paradigms  Languages can be classified as more functional or more procedural based on how much they encourage the use of statements vs expressions   For example  C would be more functional than COBOL because a function call is an expression  whereas calling a sub program in COBOL is a statement  that manipulates the state of shared variables and doesn t return a value   Python would be more functional than C because it allows you to express conditional logic as an expression using short circuit evaluation  test  amp  amp  path1    path2 as opposed to if statements   Scheme would be more functional than Python because everything in scheme is an expression   You can still write in a functional style in a language which encourages the procedural paradigm and vice versa  It s just harder and or more awkward to write in a paradigm which isn t encouraged by the language

User · Answer

To Understand the difference  one needs to to understand that  the godfather  paradigm of both procedural and functional programming is the imperative programming   Basically procedural programming is merely a way of structuring imperative programs in which the primary method of abstraction is the  procedure    or  function  in some programming languages   Even Object Oriented Programming is just another way of structuring an imperative program  where the state is encapsulated in objects  becoming an object with a  current state   plus this object has a set of functions  methods  and other stuff that let you the programmer manipulate or update the state   Now  in regards to functional programming  the gist in its approach is that it identifies what values to take and how these values should be transferred   so there is no state  and no mutable data as it takes functions as first class values and pass them as parameters to other functions    PS  understanding every programming paradigm is used for should clarify the differences between all of them   PSS  In the end of the day  programming paradigms are just different approaches to solving problems   PSS  this quora answer has a great explanation

User · Answer

A functional programming is identical to procedural programming in which global variables are not being used

[functional-programming] What is the difference between procedural programming and functional programming?

Examples related to functional-programming

Examples related to glossary

Examples related to paradigms

Examples related to procedural-programming