Theoretical Concepts For The Parsing Assignment

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Theoretical Concepts For The Parsing Assignment
A return to the compilation process Parsing and
Formal grammars Divide and conquer through
recursion
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Compilation
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Parts Of The Compiler
Back end
Front end
Lexical analyzer Syntax analyzer Semantic analyzer
Translates to target language
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The Lexical Analyzer

• Groups symbols together into entities

w h i l e
while
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Syntax Analyzer (Parser)

• Analyzes the structure of the program in order to
  group together related symbols

while (i lt 5) statement statement

while (i lt 5) statement
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Semantic analyzer

• Determines the meaning
• int num
• double db

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Assignment 4

• With a given English phrase your program must
  perform
• A lexical analysis
• A syntactical analysis (parse the phrase)
• Needs a formal grammar

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A Perspective Into Assignment 4
Perform a syntactical analysis
.
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A Perspective Into Assignment 4 (2)

• Conjunctions must be handled recursively

Jack and Jill or Bob and Bill went up the hill.
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Backus-Naur Form (BNF)

• An example of a formal grammar
• Can be used in the fourth assignment to specify
  the syntax of the language (grammatically
  correct)
• Introduced by Jim Backus and developed by Pete
  Naur to specify the syntax rules for Algol 60

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BNF General Examples

• Example one
• ltAgt ltB1gt ltB2gt ltB3gtltBngt
• Example two (alternatives)
• ltAgt ltB1gt ltB2gt ltB3gt ltB2gt ltB4gt ltB1gt
• Example three (program specification)
• x x 1
• ltAssignment statementgt ltvariablegt lt gt
  ltexpressiongt

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BNF Assignment 4

• (The following specifications come from the main
  233 course web page www.cpsc.ucalgary.ca/becker/
  233)
• ltSTATEMENTgt ltSentencegt ltPUNCTgt
• ltSentencegt ltNounPhrasegt ltVerbPhrasegt 
• ltNounPhrasegt ltVerbPhrasegt ltConjunctiongt
  ltSentencegt
• ltNounPhrasegt ltProNoungt ltProperNoungt
  ltArticlegt ltAdjectiveListgt ltNoungt ltArticlegt
  ltNoungt ltNoungt

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BNF Assignment 4

• ltVerbPhrasegt ltAdverbListgt ltVerbgt ltVerbgt
  ltAdverbListgt
• ltVerbgt ltNounPhrasegt ltAdverbListgt
• ltAdverbListgt ltVerbgt ltNounPhrasegt
• ltVerbgt
• ltAdjectiveListgt ltAdjectiveListgt ltAdjectivegt
  ltnothinggt
• ltAdverbListgt ltAdverbListgt ltConjunctiongt
  ltAdverbgt ltAdverbgt

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Syntax Diagrams

• An alternative method for representing a formal
  language

ltgt
ltgt
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Syntax Diagrams General Examples

• Example one
• Example two

i 1, 2, 3n
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Syntax Diagrams General Examples (2)

• Example three (program specification)
• x x 1

ltAssignment statementgt
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Syntax Diagrams Assignment 4
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Syntax Diagrams Assignment 4 (2)
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Syntax Diagrams Assignment 4 (3)
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Syntax Diagrams Assignment 4 (4)
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Divide And Conquer

• Split the problem into sub-problems (through
  recursive calls)
• Continue splitting each of the sub-problems into
  smaller parts until you cannot split the problem
  up any further
• Solve each of the sub-problems and combine the
  solutions yielding the solution to the original
  problem

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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
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Divide And Conquer An Example
Final result after recursive calls 5
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Divide And Conquer Example
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Divide And Conquer Example

• The complete source and executable files can be
  found in Unix under the directory
• /home/profs/tamj/233/examples/recursion

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The Driver Class

• class Driver
• public static void main (String argv)
• NumberList list new NumberList ()
• Adder listAdder new Adder()
• int total listAdder.divideAndAdd(list.ge
  tList(),
• 
  list.getLow(),
• 
  list.getHigh())
• System.out.println()
• System.out.println("SUM OF LIST..."
  total)
• System.out.println()

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The NumberList Class

• class NumberList
• private char list
• private int low
• private int high
• public NumberList ()
• int i, noElements
• System.out.print("Enter number of array
  elements ")
• high Console.in.readInt()
• Console.in.readChar()
• high high - 1
• low 0
• list new char high1
• defaultInitialization()
• displayList()

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The NumberList Class (2)

• public void defaultInitialization ()
• int i
• for (i low i lt high i)
• if (i 2 0)
• listi '1'
• else
• listi ''

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The NumberList Class (3)

• public void displayList ()
• int i
• System.out.println()
• System.out.print("Displaying the number
  list ")
• System.out.println (list)
• System.out.println()

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Class Adder AsciiToInteger

• class Adder
• private int asciiToInteger (char ch)
• int temp
• // Recall that the ascii value for the
  character '0' is 48.
• temp (int) (ch - 48)
• return temp

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Class Adder DivideAndAdd

• class Adder
• public int divideAndAdd (char array, int
  low, int high)
• System.out.println("SUBDIVIDED ARRAY "
  "low" low " " "high" high)

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Class Adder DivideAndAdd (2)

• // THREE BASE CASES
• // One element in sublist convert from
  char to int and return if it's a number.
• if (low high)
• if (arraylow ! '')
• int temp asciiToInteger(arraylo
  w)
• return temp
• else
• // It's a plus sign don't sum the
  ascii value.
• return(0)

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Class Adder DivideAndAdd (3)

• // Two elements in sublist
• if ((low1)high)
• // Order of elements operation,
  operand
• if (arraylow '')
• int temp asciiToInteger
  (arrayhigh)
• return temp
• // Order of elements operand,
  operation
• else if (arrayhigh '')
• int temp asciiToInteger
  (arraylow)
• return temp

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Class Adder DivideAndAdd (4)

• // Three elements in sublist
• if ((low2) high)
• // Order of elements ltoperandgt
  ltoperationgt ltoperandgt
• if (arraylow ! '')
• int operand1 asciiToInteger(arra
  ylow)
• int operand2 asciiToInteger(arra
  yhigh)
• return (operand1operand2)
• // Order of elements ltoperationgt
  ltoperandgt ltoperationgt
• else
• int temp asciiToInteger(arraylo
  w1)
• return temp

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Class Adder DivideAndAdd (5)

• // RECURSIVE CASES
• // More than four elements in the list.
• int middle, leftTotal, rightTotal, total
• int leftLow, leftHigh, rightLow,
  rightHigh
• middle (int) ((lowhigh)/2)
• // Set low and high bound for the left
  sublist.
• leftLow low
• leftHigh middle - 1
• // Set low and high bound for the right
  sublist.
• rightLow middle 1
• rightHigh high
• leftTotal divideAndAdd(array, leftLow,
  leftHigh)
• rightTotal divideAndAdd(array,
  rightLow, rightHigh)

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Class Adder DivideAndAdd (7)

• total leftTotal rightTotal
• if (arraymiddle ! '')
• total total asciiToInteger(arraym
  iddle)
• // Recursive calls finished.
• return total

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Summary

• You should now know
• Compilation What are the major parts of a
  compiler
• How formal grammars can be used to specify the
  syntax of a language
• Two examples of specifying syntax rules
• Backus-Naur form (BNF)
• Syntax diagrams
• Divide and Conquer through recursion