SNOBOL4

1
SNOBOL4

• CSC 507
• Hwan-Jun, Lee
• 11/29/2005

2
Content of Presentation

• Introduction
• Significant Features of SNOBOL
• Pattern Matching
• Primitive Functions
• Predicates
• Programmer-Defined Functions
• Array, Table and Defined Data Types

3
Introduction

• SNOBOL StriNg Oriented symBOlic
  Language
• Developed by Ralph Griswold aad associates at
  Bell Labs (where C/C) in 1963
• SNOBOL is a special purposed language developed
  to provide a powerful means for the manipulation
  of strings of symbols
• Evolved throughout 1960s ( latest version SNOBOL4
  )

4
Evolution of PLs
5
Significant Features of SNOBOL

• String Manipulation Operations - allow a string
  to be tested and make replacement.
• Built-In string pattern-matching examine the
  occurrence of specified pattern.
• Dynamically Typed
• No type declaration,
• No restrictions on the data type of the value
  of any variable.

6
Significant Features of SNOBOL cont

• Interpretive language compiler translates the
  program into a notation that interpreter execute.
• Garbage-collected
• Suitable for text-manipulation and processing
• Pattern matching, goto and label

7
Pattern Matching

• Pattern Matching Statement
• No explicit pattern matching operator
• Form subject pattern
• Example
• TRADE PROGRAMMER
• TRADE GRAM

8
Pattern Matching cont

• Replacement Statement
• Form subject pattern object
• Example
• WORD GRID
• WORD I OU
• I is replaced by OU
• WORD gt GROUD

9
Pattern Matching cont

• Alternation - Builds a new pattern from its
  alternatives.
• P3 P1 P2
• Builds a new pattern and assigns it as the value
  of P3.

10
Pattern Matching cont

• Concatenation Concatenate strings or
  patterns.
• P6 P4 P5
• No explicit operator
• Expressions are separated by one or more blanks.

11
Pattern Matching cont

• Example
• P BE BEA BEAR
• Q RO ROO ROOS
• R DS D
• S TS T
• PAT P R Q S
• ( same as PAT (P R) (Q S), concatenation has
  higher precedence than alternation )
• PAT matches the followings
• BEDS BED BEADS BEAD BEARDS BEARD
• ROTS ROOT ROT ROOSTS ROOTS ROOST

12
Pattern Matching cont

• Conditional value Assignment
• BR (B R) . FIRST
• Upon successful completion of pattern matching,
  the substring matched becomes
• the values of FIRST
• Immediate Value Assignment
• BR B FIRST E SECOND
• Whenever B matches, the substring immediately
  becomes the value of FIRST
• Example
• BR (B R) . FIRST (E EA) (D
  DS) . LAST
• BED BR FIRST I LAST ( gt replacement )
• BED changed into BID

13
Pattern Matching cont

• Primitive Functions
• LEN(integer) matches any string of
• specified length.
• SPAN(string) - matches runs of characters
• BREAK(string) matches everything upto.
• Ex
• IT RUNS. BREAK( ) SPAN( ) BREAK(.) .
• gt Pattern matches.

14
Pattern Matching cont

• Primitive Functions
• ANY(string) matches any single chracters
• EX ANY(AEIOU) gtmatch any vowel
• same as A E I O U
• NOTANY(string)
• TAB(interger) matches all characters from the
  current cursor position up to integer

15
Pattern Matching cont

• Example
• reformatting 1290 SEP. 27
• 1293 MAY 20
• to SEP. 27, 1290
• MAY 20, 1293
• 
  
• ANCHOR 1
• DATE LEN(4) . YR LEN(4) . MO
  LEN(2) . DAY
• LOOP CARD INPUT F(END)
• CARD DATA MO DAY , YR
  F(ERROR)
• OUTPUT CARD (LOOP)
• ERROR OUTPUT CARD IMPROPERLY FORMATTED.
  (LOOP)
• END
• 
  

16
Primitive Functions

• LEN(), SPAN(), BREAK(), ANY(), NOTANY(), TAB()
• IDENT(arg1,arg2)
• Argument can be any type
• On success, arg1 becomes the value of function
  call
• On fail, function call fails.
• IDENT(APPLE) gt fails
• IDENT(3, 3.0) gt fails
• DIFFER(BCD,B CD) gtfails
• SIZE(abc) gt 3
• NEW_S REPLACE(S, .,?!, ) gt
  replace all punctuation marks in S with blanks
  and return it.
• NEW_S TRIM(ABC ) gt remove trailing blanks.
• DUPL(ABC, 10) gt duplicate ABC 10 times.
• OUPUT DUPL(DUPL( ,10 SIZE(ABC)) ABC,
  5)
• gt 5 lines of ABC
• OUTPUT REMDR(15,2) gt prints 1
• OUTPUT REMDR(15, -4) gt prints 3 (the sign of
  REMDR is the sign of f.a

17
Predicates

• Testing relations b/w arguments
• On success, null for the call
• GE(17.0, 3) gt succeeds
• LT(17.0, 3) gt fails
• EQ(2) gt fails, EQ(2, NULL) EQ(2, 0)
• Numerical predicates are used for loop
• LOOP N LT(N, M) N 1 S(LOOP)F(OUT)

18
Programmer-Defined Functions

• call primitive function DEFINE() to define
• programmer-defined function.
• DEFINE(PROTOTYPE, ENTRYLABEL)
• DEFINE() must be executed before the call is
  made.
• Example
• DEFINE(F(X,Y)L1, L2, FENTRY)
• DEFINE(G(Z), GENT)
• DEFINE(MARK())

19
Programmer-Defined Functionscont

• Before execution of function begins
• The name of the function
• All formal arguments
• All local variables are saved
• It is possible for a function to be recursive
• New values are assigned to variables as follows
• The name of the function is assigned null
• Formal arguments are assigned their values
• All local variables are assigned null

20
Programmer-Defined Functionscont

• Example
• DEFINE(UNION(X,Y)CH,UN)
• ZSET Z SET1 UNION(SET2, SET3) SET4
• UN UNION X
• ULOOP Y LEN(1) . CH F(RETURN)
• UNION BREAK(CH) S(ULOOP)
• UNION UNION CH (ULOOP)

21
Programmer-Defined Functionscont

• Example Decimal to Binary Conversion,
  Using Recursion
• DEFINE(BINARY(N)) F(BINEND)
• BINARY BINAY GT(N,1) BINARY(N/2) REMDR(N,2)
• S(RETURN)
• BINARY N (RETURN)
• BINEND
• GT(N,1) TESTS THE CASES N 0 OR 1
• N / 2 RETURNS INTEGER

22
Array, Table and Defined Data Types

• ARRAY(prototype, initValue)
• Indexing starts at 1
• Each element may have any type ( integer,
  pattern..
• VECTOR ARRAY(10)
• gt one-dimensional array of length 10, null
• LINE ARRAY(-55)
• gt one-dimensional array, upper bound 5,
  lower bound -5
• BOARD ARRAY(3,3,X)
• gt three-by-three array
• A1 ARRAY(5)
• A2 ARRAY(5, A1)
• Each element of A2 has the same array A1.
• OUPUT BOARDlt2,3gt gtprints out the value of 2,3
  element

23
Array, Table and Defined Data Types

• ARRAY
• A ARRAY(3)
• B A
• gt A and B have the same array ( like pointers
  pointing at the same object)
• COPY function produces a copy of an array.
• A ARRAY(3)
• Alt2gt TWO
• B COPY(A)
• Blt2gt SIX
• gt A and B point two distinct physical objects

24
Array, Table and Defined Data Types

• TABLE(N,M)
• Default of N,M 10
• Similar to a one-dimensional array but variable
  in a table can be referenced by an y data object.
  ( array integer reference )
• N initial size of the table
• M - of additional variables if needed
• TABLE(20, 15) gt20, 35, 50,
• T TABLE()
• TltAgt 3

25
Array, Table and Defined Data Types

• Programmer-Defined Data Type
• DATA(P) defines a new data type.
• Example
• DATA(COMPLEX(R,I))
• gt creates a new type COMPLEX which has
• two fields (R, I)
• gt No limit to the number of fields.
• C COMPLEX(1.5, 2.0)
• A R(C) gt the first field is referenced
• R(C) 3.2 gt assign value to the first field

26
SNOBOL4 Interpreters

• The Minnesota SNOBOL4 Interpreter
• Runs SNOBOL4 under the IBM Disk Operating System
  (IBM DOS), MS DOS, OS/2, Windows 95 and others.

27
Reference

• http//www.snobol4.org/
• http//www.sachsdavis.clara.net
• http//www.atariarchives.org
• http//calico.org/journalarticles