What is parsing in terms that a new programmer would understand

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I am a college student getting my Computer Science degree   A lot of my fellow students really haven t done a lot of programming   They ve done their class assignments  but let s be honest here those questions don t really teach you how to program     I have had several other students ask me questions about how to parse things  and I m never quite sure how to explain it to them   Is it best to start just going line by line looking for substrings  or just give them the more complicated lecture about using proper lexical analysis  etc  to create tokens  use BNF  and all of that other stuff   They never quite understand it when I try to explain it   What s the best approach to explain this without confusing them or discouraging them from actually trying

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In linguistics  to divide language into small components that can be analyzed  For example  parsing this sentence would involve dividing it into words and phrases and identifying the type of each component  e g  verb  adjective  or noun    Parsing is a very important part of many computer science disciplines  For example  compilers must parse source code to be able to translate it into object code  Likewise  any application that processes complex commands must be able to parse the commands  This includes virtually all end-user applications   Parsing is often divided into lexical analysis and semantic parsing  Lexical analysis concentrates on dividing strings into components  called tokens  based on punctuationand other keys  Semantic parsing then attempts to determine the meaning of the string   http   www webopedia com TERM P parse html

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Simple explanation  Parsing is breaking a block of data into smaller pieces  tokens  by following a set of rules  using delimiters for example    so that this data could be processes piece by piece  managed  analysed  interpreted  transmitted  ets    Examples  Many applications  like Spreadsheet programs  use CSV  Comma Separated Values  file format to import and export data  CSV format makes it possible for the applications to process this data with a help of a special parser  Web browsers have special parsers for HTML and CSS files  JSON parsers exist  All special file formats must have some parsers designed specifically for them

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I d explain parsing as the process of turning some kind of data into another kind of data   In practice  for me this is almost always turning a string  or binary data  into a data structure inside my Program   For example  turning    Nick User Host PRIVMSG  channel  Hello     into  C   struct irc line       char  nick      char  user      char  host      char  command      char   arguments      char  message    sample      Nick    User    Host    PRIVMSG       channel      Hello

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Parsing to me is breaking down something into meaningful parts    using a definable or predefined known  common set of part  definitions    For programming languages there would be keyword parts  usable punctuation sequences     For pumpkin pie it might be something like the crust  filling and toppings   For written languages there might be what a word is  a sentence  what a verb is     For spoken languages it might be tone  volume  mood  implication  emotion  context  Syntax analysis  as well as common sense after all  would tell if what your are parsing is a pumpkinpie or a programming language  Does it have crust  well maybe it s pumpkin pudding or perhaps a spoken language    One thing to note about parsing stuff is there are usually many ways to break things into parts    For example you could break up a pumpkin pie by cutting it from the center to the edge or from the bottom to the top or with a scoop to get the filling out or by using a sledge hammer or eating it   And how you parse things would determine if doing something with those parts will be easy or hard   In the  computer languages  world  there are common ways to parse text source code  These common methods  algorithims  have titles or names  Search the Internet for common methods names for ways to parse languages  Wikipedia can help in this regard

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Parsing is the process of analyzing text made of a sequence of tokens to determine its grammatical structure with respect to a given  more or less  formal grammar     The parser then builds a data structure based on the tokens   This data structure can then be used by a compiler  interpreter or translator to create an executable program or library     source  wikimedia org     If I gave you an english sentence  and asked you to break down the sentence into its parts of speech  nouns  verbs  etc    you would be parsing the sentence   That s the simplest explanation of parsing I can think of   That said  parsing is a non-trivial computational problem   You have to start with simple examples  and work your way up to the more complex

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What is parsing   In computer science  parsing is the process of analysing text to determine if it belongs to a specific language or not  i e  is syntactically valid for that language s grammar   It is an informal name for the syntactic analysis process   For example  suppose the language a n b n  which means same number of characters A followed by the same number of characters B   A parser for that language would accept AABB input and reject the AAAB input  That is what a parser does   In addition  during this process a data structure could be created for further processing  In my previous example  it could  for instance  to store the AA and BB in two separate stacks   Anything that happens after it  like giving meaning to AA or BB  or transform it in something else  is not parsing  Giving meaning to parts of an input sequence of tokens is called semantic analysis    What isn t parsing    Parsing is not transform one thing into another  Transforming A into B  is  in essence  what a compiler does  Compiling takes several steps  parsing is only one of them    Parsing is not extracting meaning from a text  That is semantic analysis  a step of the compiling process      What is the simplest way to understand it   I think the best way for understanding the parsing concept is to begin with the simpler concepts  The simplest one in language processing subject is the finite automaton  It is a formalism to parsing regular languages  such as regular expressions   It is very simple  you have an input  a set of states and a set of transitions  Consider the following language built over the alphabet   A  B    L     w   w starts with  AA  or  BB  as substring    The automaton below represents a possible parser for that language whose all valid words starts with  AA  or  BB        A-- gt  q1 --A-- gt  qf           q0                         B-- gt  q2 --B-- gt  qf    It is a very simple parser for that language  You start at  q0   the initial state  then you read a symbol from the input  if it is A then you move to  q1  state  otherwise  it is a B  remember the remember the alphabet is only A and B  you move to  q2  state and so on  If you reach  qf  state  then the input was accepted   As it is visual  you only need a pencil and a piece of paper to explain what a parser is to anyone  including a child  I think the simplicity is what makes the automata the most suitable way to teaching language processing concepts  such as parsing   Finally  being a Computer Science student  you will study such concepts in-deep at theoretical computer science classes such as Formal Languages and Theory of Computation

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Parsing is about READING data in one format  so that you can use it to your needs   I think you need to teach them to think like this  So  this is the simplest way I can think of to explain parsing for someone new to this concept   Generally  we try to parse data one line at a time because generally it is easier for humans to think this way  dividing and conquering  and also easier to code   We call field to every minimum undivisible data  Name is field  Age is another field  and Surname is another field  For example   In a line  we can have various fields  In order to distinguish them  we can delimit fields by separators or by the maximum length assign to each field   For example  By separating fields by comma  Paul 20 Jones  Or by space  Name can have 20 letters max  age up to 3 digits  Jones up to 20 letters   Paul nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp 020Jones nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   Any of the before set of fields is called a record   To separate between a delimited field record we need to delimit record  A dot will be enough  though you know you can apply CR LF    A list could be   Michael 39 Jordan Shaquille 40 O neal Lebron 24 James   or with CR LF  Michael 39 Jordan Shaquille 40 O neal Lebron 24 James  You can say them to list 10 nba  or nlf  players they like  Then  they should type them according to a format  Then make a program to parse it and display each record  One group  can make list in a comma-separated format and a program to parse a list in a fixed size format  and viceversa

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Have them try to write a program that can evaluate arbitrary simple arithmetic expressions  This is a simple problem to understand but as you start getting deeper into it a lot of basic parsing starts to make sense

[parsing] What is parsing in terms that a new programmer would understand?

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