Recursive Data Structures Implementation: Linear Lists

Chapter 3.2 Recursive Data Structures Part 1 : Linear Lists

Name Father Mother A Recursive Data StructureExample : A Pedigree Person : Myself Myfather Mymother Mygrandfather Mygrandmother Mygrandfather Mygrandmother

Father Mother Recursive Data StructuresImplementation by variant records : Not allowed Known UnKnown Name TYPEPerson = RECORD CASEKnown : BOOLEANOF TRUE: Name : String; Father, Mother : Person | FALSE : (* empty *) END END Syntax error

Name Name Name Name Name Name Father Father Father Father Father Father Mother Mother Mother Mother Mother Mother Recursive Data StructuresImplementation by variant pointers TYPE Link = POINTER TO Person; Person = RECORD Name : String; Father, Mother : Link END

Variables Number, size and address of variables is KNOWN UNKNOWN at compile time Such variables are called STATIC DYNAMIC They are declared in a block named created at run time anonymous

Simple Types • Ordinal Types • REAL Type • POINTER Type • Value = address • Allow indirect access to dynamic (anonymous) variables • Used for • recursive data structures • hidden data types in modules

Dynamic Variables • Created at run-time by the procedure NEW(p) • Type determined by declaration of pointer p • Anonymous • Accessed indirectly via the pointer variable p • Can be deleted at run-time by the procedure DISPOSE(p) • Some versions of Modula 2 use • ALLOCATE(p, SIZE(type of dynamic variable)) • DEALLOCATE (p, SIZE(type of dynamic variable))

Type POINTER TO Pointer Identifier ^ Pointers Syntax POINTER Type Dynamic Variable

Common RecursiveData Structures Linear Lists Binary Trees

Linear List Example • Specification : • Each line of a text should be reversed • End Of Line detected by function EOLN • End Of Text detected by function EOF • Solution : • Read each character of a line into a linear list • Write the characters of the linear list in the reverse order they were entered. This is an example sihT si elpmaxe na

Linear List ExampleData Declarations TYPE Link = POINTER TO Item; Item = RECORD Ch : CHAR; Next : Link END; VAR First, p : Link

Linear List ExampleLinked List Building First p WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

First Linear List ExampleLinked List Building p WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch:=RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T h WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T i h WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T s i h WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); First:= First^.Next; END; WrLn; END;(* Line handling *) s

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); First:= First^.Next; END; WrLn; END;(* Line handling*) s

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); First:= First^.Next; END; WrLn; END;(* Line handling*) si

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); First:= First^.Next; END; WrLn; END;(* Line handling*) sih

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); First:= First^.Next; END; WrLn; END;(* Line handling*) sihT

Linear List ExampleLinked List Building First p T s i h WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Building First p T i s i h WHILE NOT EOF DO First := NIL; WHILE NOT EOLN DO NEW(p); p^.Next := First; First := p; p^.Ch := RdChar(); END; This is an example

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); p := First; First:= First^Next; DISPOSE(p) END; WrLn; END;(* Line handling *)

Linear List ExampleLinked List Writing First p T s i h WHILE First # NIL DO WrChar(First^.Ch); p := First; First:= First^Next; DISPOSE(p) END; WrLn; END;(* Line handling *) s

Linear List ExampleLinked List Writing First p T i h WHILE First # NIL DO WrChar(First^.Ch); p := First; First:= First^Next; DISPOSE(p) END; WrLn; END;(* Line handling *) s

Linear List ExampleLinked List Writing First p T i h WHILE First # NIL DO WrChar(First^.Ch); p := First; First:= First^Next; DISPOSE(p) END; WrLn; END;(* Line handling *) si

Linear List ExampleLinked List Writing First p T h WHILE First # NIL DO WrChar(First^.Ch); p := First; First:= First^Next; DISPOSE(p) END; WrLn; END;(* Line handling *) si

Recursive Data Structures Implementation: Linear Lists