1. By: Bahman Ravaei 790649 Farhad Rad 116703 81-82-2 نیمسال
SNOBOL 4
By: Bahman Ravaei
Farhad Rad
نیمسال

2. Introduction to the snobol 4 P.L
Developed at BELL laboratories in 1962
Is a string of characters (character oriented)
Define other data type
Consist of a sequence of statement
Array and Table have more flexibility
Function calls can be made recursively
Link list node and complex number are possible programmer define data type

3. four basic type of statements:
i) the Assignment statement
ii) the Pattern matching statements
iii) the Replacement statement
iv) the End statement

4. Assignment statements :
the simple type of assignment: variable = value example: v = 5
the value may be given an experssion example: W = ( ) which assigns the value 20 to the variable w

5. “BLANK are required around arithmetic operators”
The value may be string of characters example: v = ‘dog’

6. Arithmetic:
i) Integers ii) Real arithmetic operation is “addition +” ,”subtraction -” ,”multiplication * ” ,”division / ” and “exponentiation ** or !” blanks are required between the binary operators and their operands ,Unary operator such as the minus sign must be adjacent to their operands. example: Q2 = -P / -N

7. Predicates of arithmetic operations :
-Unary operators -Exponentiation -Multiplication and Division -Addition and Subtraction
All arithmetic operations associate to the left except exponentiation . example : ** 3 ** 5 is equivalent to : ** (3 ** 5)

8. Example : m = 4 n = 5 p = n * m / (n - 1) assign the value 5 to p
Example : pi = mul = 2. * pi * assign Real value to pi and mul

9. Pattern matching statements:
Define : The operation of examining for occurrence of specified substring
Pattern matching have two type: i ) the pattern matching statement ii ) the replacement statement

10. the pattern matching statement :
the pattern matching statement has the form : subject pattern two fields separated by at least one blank example: trade = ‘programmer ’ trade ‘gram’
Pattern can an expression row = ‘k’ no. = ‘kk2429’ row no pattern is equivalent by ‘k24’

11. Replacement statements
The replacement statement has the form subject pattern = object
If the pattern matching operation succeeds the subject string is modified by replacing the matched substring by the object . example: WORD = “GRID” WORD ‘I’ = ‘OU’ thus WORD is equivalent GROUD

12. If pattern not found the statement failed example:
If pattern not found the statement failed example: WORD ‘AB’ = ‘OU’ example: HAND = ‘AC4DAHDKS’ RANK = 4 SUIT = ‘D’ HAND RANK SUIT = ‘AS’ first RANK and SUIT concatenate that it’s 4D and later HAND ‘4D’ = ‘AS’ example : HAND RANK SUIT =

13. Patterns
Two operation available for constructing complex patterns: i) alternation ii) concatenation alternation is indicated by expression of the form: P1 | P2 example: KEYWORD = ‘COMPUTER’ | ‘PROGRAM’ KEYWORD = KEYWORD | ‘ALGORITM’

14. can use KEYWORD to pattern field:
TEXT = ‘PROGRAMMING ALGORITM FOR COMPUTERS ‘
TEXT KEYWORD = after matching: TEXT = ‘MING ALGORITM FOR COMPUTERS’

15. Concatenation
Concatenation of two patterns ,P1 and P2 ,is specified in the same way as the concatenation of two strings: P1 P2 example: BASE = ‘BINARY’ | ‘DECIMAL’ | ‘HEX’ SCALE = ‘FIXED’ | ‘FLOAT’ ATTRIBUTE = SCALE BASE

16. Array :
Arrays are created by function ARRAY . ARRAY (p , e) example : board = ARRAY (‘3,3’ , ‘x’) x X

17. Example :
A1 = ARRAY ( 5 ) A2 = ARRAY (5 , A1) A A1

18. Flow of control
A SNOBOL program is a sequence of statements terminated by an end statement . labels and goto provide to control the flow of the program.
Example of label: START TEXT = INPUT
the end statement is distinguished by the label END

19. Transfer to a labelled statement is specified in the goto field which may appear at the end of a statement and is separated from the rest of the statement by a colon ‘ : ’.
Two types of transfers can be specified in the goto field : i ) conditional ii ) unconditional

20. conditional
A conditional transfer consists of a label enclosed within parentheses preceded by an F or S corresponding to Failure or Success. example : TEXT = INPUT :F(DONE) example : LOOP PUNCH = INPUT S:LOOP END

21. we can use F and S in one statement example:
we can use F and S in one statement example: COLOR = ‘RED’ | ‘GREEN’ | ‘BLUE’ BRIGHT TEXT COLOR = :S(BRIGHT)F(BLAND) BLAND …….

22. unconditional
An unconditional transfer is indicated by the absence of an F or S before the enclosing parentheses . example: LOOP PUNCH = INPUT :F(END) OUTPUT = PUNCH :(LOOP) END

23. Indirect reference
Indirect referencing is indicated by the unary operator $. examples: i) MONTH = ‘APRIL’ $MONTH = ‘CRUEL’ is equivalent: APRIL = ‘CRUEL’ ii) WORD = ‘RUN’ $(WORD ‘:’) = $(WORD ‘:’) iii) $(‘A’ | ‘B’) iv) N = N :($(‘PHASE’ N))

24. Functions:
i) primitive functions ii) predicates iii) defined functions

25. Primitive function
Many snobol procedure are invoked by function built into the system ,called primitive functions. Few example of primitive function: i) SIZE (string) APE = ‘SIMIAN’ OUTPUT = SIZE(APE) ii) DUPL (string ,integer) DUPL(‘/*’,5)
iii) REPLACE( TEXT,CH1,CH2) STATEMENT = ‘A(I,J) = A(I,J) + 3’ OUTPUT = REPLACE(STATEMENT,’()’,’<>’) print the line : A<I,J> = A<I,J> + 3

26. Predicate:
A function or operation that returns the NULL string if a given condition is satisfied.
Example:
i) LE(n1 , n2 )
PUNCH = LE( SIZE(TEXT),80) TEXT
ii) LT( n1 , n2 )
ADD N = LT( N , 50 ) N+1
iii) DIFFER ( st1 , st2 )
OUTPUT = DIFFER ( FIRST , SECOND ) FIRST SECOND
iv) LGT ( st1 , st2 )

27. Defined function: A function defined by Programmer.
The primitive function DEFINE to specify the function name , formal arguments , local variables, and the entry point of the function.
Example:
DEFINE ( ‘ DELETE ( STRING , CHAR )’ , ‘D1’ )
D STRING CHAR = :S ( D1 )
DELETE = STRING : ( RETURN )

28. Example:
DEFINE ( ‘ DELETE ( STRING , CHAR )’ )
DELETE STRING CHAR = :F ( FRETURN)
D2 STRING CHAR = :S ( D1 )
DELETE = STRING : ( RETURN )

29. Programmer define data type:
The primitive function DATA can be used to difine the new data type.
Example:
DATA( ‘ NODE ( VALUE , LINK)’)
P = NODE (‘ S ‘ , )
P = NODE (‘ T ‘ , P )
P = LINK ( P ) P
‘ T ‘
‘ S’
NULL

30. Program format: Example:
OUTPUT = ‘ THE TOTAL NUMBER OF OCCURRENCE IS’ + SUM< N >
X = 2 ; Y = 3 ; Z = 10
* : THIS IS A COMMENT

31. End