1. Chapter 2.6 Modula 2 Structured Types

2. Types in Modula 2 Simple Types: values can’t be decomposed –Ordinal Types: bijection with natural numbers –Reals: approx. representation for real values –Pointers: addresses in data memory Structured Types: Values have # components –Arrays: all components have same type –Records: components can have # types –Sets: small sets of ordinal values –Procedures: entire subprograms

3. Types in Modula 2 Simple Types: values can’t be decomposed –Ordinal Types: bijection with natural numbers –Reals: approx. representation for real values –Pointers: addresses in data memory Structured Types: Values have # components –Arrays: all components have same type –Records: components can have # types –Sets: small sets of ordinal values –Procedures: entire subprograms

4. ARRAY type index typecomponent type ARRAY type

5. ARRAY element array variable designatorindex expression array element

6. ARRAY applications MonSunSatFriThuWedTue 8 19 18 17 16 15 14 13 12 11 10 9 info. teleN st.pr. teleEst.pr. teleEst.pr. info. st.pr.info. st.pr.info.

7. ARRAY applications TYPE Day = (Mon,Tue,Wed,Thu,Fri,Sat,Sun); Hour = [8..19]; Course = ARRAY[0..10] OF CHAR; Schedule = ARRAY Day, Hour OF Course; VAR RoomK1 : Schedule; BEGIN... RoomK1[Wed,8] := "info.";... END

8. Sieve of Eratosthenes Print all primes <= Max Make a set of cardinals 2 <= x <= MAX FOR all cardinals present in set Print the first cardinal x remaining in the set Remove all multiples of x from the set

9. Sieve of Eratosthenes Make a set of cardinals 2 <= x <= MAX CONST Max = 1000; VAR Sieve : ARRAY[2..Max] OF BOOLEAN; i : [2..Max];... FOR i:= 2 TO MAX DO Sieve[i] := TRUE END; (* FOR *) 2876543... FALSE TRUE

10. Sieve of Eratosthenes FOR all cardinals present in the set Print the first cardinal in the set Remove all multiples of it VAR p : CARDINAL;... FOR i := 2 TO Max DO IF Sieve[i] THEN p := i; WriteCard(p,5); WriteLn; WHILE p <= Max DO Sieve[p] := FALSE; p := p + i END (* WHILE *) END (* IF *) END (* FOR *)

11. Types in Modula 2 Simple Types: values can’t be decomposed –Ordinal Types: bijection with natural numbers –Reals: approx. representation for real values –Pointers: addresses in data memory Structured Types: Values have # components –Arrays: all components have same type –Records: components can have # types –Sets: small sets of ordinal values –Procedures: entire subprograms

12. Repairing a flat tire Refinement of “tools” Tools : –Jack : device to lift a car –Wrench : device to loose or fasten bolts

13. RECORD example TYPE Date = RECORD Day : [1.. 31]; Month : [1.. 12]; Year : [1900.. 2100] END; VAR Today : Date;

14. RECORD type END field listfields fixed fields field type

15. RECORD element record variable designator field identifier Today.Day := 20; Today.Month := 10; Today.Year := 1998; WITH Today DO Day := 20; Month := 10; Year := 1998; END

16. Nested RECORDs example (1) TYPE Date = RECORD Day : [1.. 31]; Month : [1.. 12]; Year : [1900.. 2100] END; String = ARRAY [0..29] OF Char; Identity = RECORD Name, FirstName : String; BirthPlace : String; BirthDate : Date; IssueDate : Date; END; VAR Myself : Identity; Today : Date;

17. Nested RECORDs example (2) Today.Day := 20; Today.Month := 10; Today.Year := 1998 Myself.Name := "Tiberghien"; Myself.FirstName := "Jacques"; Myself.BirthPlace := "Berchem"; Myself.BirthDate.Day := 1; Myself.BirthDate.Month := 4; Myself.BirthDate.Year := 1946; Myself.IssueDate := Today;

18. Nested RECORDs example (2) WITH Today DO Day := 20; Month := 10; Year := 1998 END; WITH Myself DO Name := "Tiberghien"; FirstName := "Jacques"; BirthPlace := "Berchem"; WITH BirthDate DO Day := 1; Month := 4; Year := 1946; END; IssueDate := Today; END

19. Variant RECORDs variant variant list variant fields

20. Variant RECORD with explicit tag field Car =RECORD Weight : CARDINAL; NumberDoors : CARDINAL; FrameId,EngineId : ARRAY[0..19] OF CHAR; Fuel :(Gasoline,FuelOil,LPG,Electricity); CASE Engine :(Explosion,Electricity) OF Explosion : NbrCylinders : CARDINAL; VolCylinders : CARDINAL | Electricity : Supply : (AC,DC); Voltage : CARDINAL; END;

21. Variant RECORD with implicit tag field Car =RECORD Weight : CARDINAL; NumberDoors : CARDINAL; FrameId,EngineId : ARRAY[0..19] OF CHAR; Fuel :(Gasoline,FuelOil,LPG,Electricity); CASE (Explosion,Electricity) OF Explosion : NbrCylinders : CARDINAL; VolCylinders : CARDINAL | Electricity : Supply : (AC,DC); Voltage : CARDINAL; END;

22. Types in Modula 2 Simple Types: values can’t be decomposed –Ordinal Types: bijection with natural numbers –Reals: approx. representation for real values –Pointers: addresses in data memory Structured Types: Values have # components –Arrays: all components have same type –Records: components can have # types –Sets: small sets of ordinal values –Procedures: entire subprograms