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Modula-2

Modula-2

Modula-2 is a pl created in 1978 by Niklaus Wirth.

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Modula-2 is a computer programming language designed and developed between 1977 and 1985 by Niklaus Wirth at the Swiss Federal Institute of Technology in Zurich (ETH Zurich) as a revision of Pascal to serve as the sole programming language for the operating system and application software for the personal workstation Lilith. The principal concepts were: The module as a compilation unit for separate compilation The coroutine as the basic building block for concurrent processes Types and procedures that allow access to machine-specific data. Modula-2 was viewed by Niklaus Wirth as a successor to his earlier programming languages Pascal and Modula. Read more on Wikipedia...


Example from hello-world:
MODULE HelloWorld; FROM Terminal2 IMPORT WriteString, WriteLn; BEGIN WriteString("Hello World"); WriteLn; END HelloWorld.
Example from the Hello World Collection:
(* Hello World in Modula-2 *) MODULE HelloWorld; FROM InOut IMPORT WriteString,WriteLn; BEGIN WriteString("Hello World!"); WriteLn; END HelloWorld.
Example from Linguist:
IMPLEMENTATION MODULE HuffChan; (* This module shows how to redefine standard IO file functions. It provides functions for reading and writing packed files opened in Raw mode. *) IMPORT IOChan, IOLink, ChanConsts, IOConsts, SYSTEM, Strings; FROM Storage IMPORT ALLOCATE, DEALLOCATE; CONST rbldFrq = 512; (* means: every 512 bytes rebuild table *) TYPE charTap = POINTER TO ARRAY [0..MAX(INTEGER)-1] OF CHAR; smbTp = POINTER TO smbT; smbT = RECORD (* Huffman's tree *) ch : CHAR; n : CARDINAL; (* frequncy of char ch *) left,right,next : smbTp; END; tblT = RECORD (* bit sequence for code *) vl : CARDINAL; (* bit sequence *) cnt : INTEGER; (* it length *) END; lclDataT = RECORD (* channel's local data *) tRoot : smbTp; htbl : ARRAY [0..255] OF tblT; (* code -> bit sequence table *) ftbl : ARRAY [0..255] OF CARDINAL; (* frequncey table *) wBf,rb1,rb2 : CARDINAL; wbc,rbc,smc : INTEGER; chid : IOChan.ChanId; END; lclDataTp = POINTER TO lclDataT; charp = POINTER TO CHAR; VAR did : IOLink.DeviceId; ldt : lclDataTp; PROCEDURE Shf(a:CARDINAL; b : INTEGER) : CARDINAL; (* shl a,b (or shr) *) BEGIN RETURN SYSTEM.CAST(CARDINAL,SYSTEM.SHIFT(SYSTEM.CAST(BITSET,a),b)); END Shf; PROCEDURE wrDword(a:CARDINAL); (* write 4 bytes to file *) BEGIN IOChan.RawWrite(ldt^.chid,SYSTEM.ADR(a),4); END wrDword; PROCEDURE rdDword() : CARDINAL; (* read 4 bytes from file *) VAR a,z : CARDINAL; BEGIN a:=0; IOChan.RawRead(ldt^.chid,SYSTEM.ADR(a),4,z); RETURN a; END rdDword; PROCEDURE wrSmb(ch : CHAR); (* write bit sequence for code ch *) VAR v,h : CARDINAL; b,c : INTEGER; BEGIN WITH ldt^ DO v:=htbl[ORD(ch)].vl; c:=htbl[ORD(ch)].cnt; IF c+wbc<=32 THEN wBf:=Shf(wBf,c); wBf:=wBf+v; wbc:=wbc+c; IF wbc=32 THEN wrDword(wBf); wBf:=0; wbc:=0; END; RETURN; END; b:=c+wbc-32; h:=Shf(v,-b); wBf:=Shf(wBf,32-wbc)+h; wrDword(wBf); wBf:=v-Shf(h,b); wbc:=b; END; END wrSmb; PROCEDURE flush(); (* write data in buffer *) BEGIN WITH ldt^ DO wBf:=Shf(wBf,32-wbc); wrDword(wBf); END; END flush; PROCEDURE getSym() : CHAR; (* find code for first bit sequence in buffer *) VAR t,i : CARDINAL; b : INTEGER; BEGIN WITH ldt^ DO IF rbc<=32 THEN rb2:=rdDword(); t:=Shf(rb2,-rbc); IF rbc=32 THEN t:=0; END; rb1:=rb1+t; rb2:=Shf(rb2,32-rbc); IF rbc=0 THEN rb2:=0; END; rbc:=rbc+32; END; FOR i:=0 TO 255 DO t:=Shf(rb1,htbl[i].cnt-32); IF t=htbl[i].vl THEN rb1:=Shf(rb1,htbl[i].cnt); b:=32-htbl[i].cnt; t:=Shf(rb2,-b); rb1:=rb1+t; rb2:=Shf(rb2,32-b); rbc:=rbc+b-32; RETURN CHR(i); END; END; END; END getSym; PROCEDURE Insert(s : smbTp); (* insert new character in Huffman's tree *) VAR cr : smbTp; BEGIN WITH ldt^ DO IF tRoot=NIL THEN cr:=tRoot; tRoot:=s; s^.next:=cr; RETURN; ELSIF tRoot^.n<=s^.n THEN cr:=tRoot; tRoot:=s; s^.next:=cr; RETURN; END; cr:=tRoot; WHILE (cr^.next<>NIL) & (cr^.next^.n>s^.n) DO cr:=cr^.next; END; s^.next:=cr^.next; cr^.next:=s; END; END Insert; PROCEDURE BuildTree(); (* build Huffman's tree *) VAR cr,ocr,ncr : smbTp; BEGIN WITH ldt^ DO LOOP ocr:=NIL; cr:=tRoot; WHILE cr^.next^.next<>NIL DO ocr:=cr; cr:=cr^.next; END; NEW(ncr); ncr^.n:=cr^.n+cr^.next^.n; ncr^.left:=cr; ncr^.right:=cr^.next; IF ocr<>NIL THEN ocr^.next:=NIL; Insert(ncr); ELSE tRoot:=NIL; Insert(ncr); EXIT; END; END; END; END BuildTree; PROCEDURE BuildTable(cr: smbTp; vl,n: CARDINAL); (* build table: code -> bit sequence *) BEGIN WITH ldt^ DO IF cr^.left=NIL THEN htbl[ORD(cr^.ch)].vl:=vl; htbl[ORD(cr^.ch)].cnt:=n; DISPOSE(cr); RETURN; END; vl:=vl*2; BuildTable(cr^.left,vl,n+1); BuildTable(cr^.right,vl+1,n+1); DISPOSE(cr); END; END BuildTable; PROCEDURE clcTab(); (* build code/bitseq. table from frequency table *) VAR i : CARDINAL; s : smbTp; BEGIN WITH ldt^ DO tRoot:=NIL; FOR i:=0 TO 255 DO NEW(s); s^.ch:=CHR(i); s^.n:=ftbl[i]; s^.left:=NIL; s^.right:=NIL; s^.next:=NIL; Insert(s); END; BuildTree(); BuildTable(tRoot,0,0); END; END clcTab; PROCEDURE iniHuf(); VAR i : CARDINAL; BEGIN WITH ldt^ DO FOR i:=0 TO 255 DO ftbl[i]:=1; END; wBf:=0; wbc:=0; rb1:=0; rb2:=0; rbc:=0; smc:=0; clcTab(); END; END iniHuf; PROCEDURE RawWrite(x: IOLink.DeviceTablePtr; buf: SYSTEM.ADDRESS; len: CARDINAL); VAR i : CARDINAL; ch : CHAR; cht : charTap; BEGIN IF len = 0 THEN RETURN; END; ldt:=SYSTEM.CAST(lclDataTp,x^.cd); cht:=SYSTEM.CAST(charTap,buf); WITH ldt^ DO FOR i:=0 TO len-1 DO ch:=cht^[i]; wrSmb(ch); IF ch = 377C THEN wrSmb(ch); END; ftbl[ORD(ch)]:=ftbl[ORD(ch)]+1; smc:=smc+1; IF smc=rbldFrq THEN clcTab(); smc:=0; END; END; END; x^.result:=IOChan.ReadResult(ldt^.chid); END RawWrite; PROCEDURE RawRead(x: IOLink.DeviceTablePtr; buf: SYSTEM.ADDRESS; blen: CARDINAL; VAR len: CARDINAL); VAR i : CARDINAL; cht : charTap; ch : CHAR; BEGIN ldt:=SYSTEM.CAST(lclDataTp,x^.cd); cht:=SYSTEM.CAST(charTap,buf); IF (blen=0) OR (x^.result<>IOConsts.allRight) THEN len:=0; RETURN; END; WITH ldt^ DO FOR i:=0 TO blen-1 DO ch:=getSym(); IF ch = 377C THEN ch:=getSym(); IF ch = 0C THEN x^.result:=IOConsts.endOfInput; len:=i; cht^[i]:=0C; RETURN; END; END; cht^[i]:=ch; ftbl[ORD(ch)]:=ftbl[ORD(ch)]+1; smc:=smc+1; IF smc=rbldFrq THEN clcTab(); smc:=0; END; END; len:=blen; END; END RawRead; PROCEDURE CreateAlias(VAR cid: ChanId; io: ChanId; VAR res: OpenResults); VAR x : IOLink.DeviceTablePtr; BEGIN IOLink.MakeChan(did,cid); IF cid = IOChan.InvalidChan() THEN res:=ChanConsts.outOfChans ELSE NEW(ldt); IF ldt=NIL THEN IOLink.UnMakeChan(did,cid); res:=ChanConsts.outOfChans; RETURN; END; x:=IOLink.DeviceTablePtrValue(cid,did,IOChan.notAvailable,""); ldt^.chid:=io; x^.cd:=ldt; x^.doRawWrite:=RawWrite; x^.doRawRead:=RawRead; res:=ChanConsts.opened; iniHuf(); x^.result:=IOConsts.allRight; END; END CreateAlias; PROCEDURE DeleteAlias(VAR cid: ChanId); VAR x : IOLink.DeviceTablePtr; BEGIN x:=IOLink.DeviceTablePtrValue(cid,did,IOChan.notAvailable,""); ldt:=x^.cd; IF ldt^.rbc=0 THEN wrSmb(377C); wrSmb(0C); flush(); END; DISPOSE(ldt); IOLink.UnMakeChan(did,cid); END DeleteAlias; BEGIN IOLink.AllocateDeviceId(did); END HuffChan.
Example from Wikipedia:
ABS EXCL LONGINT REAL BITSET FALSE LONGREAL SIZE BOOLEAN FLOAT MAX TRUE CAP HALT MIN TRUNC CARDINAL HIGH NIL VAL CHAR INC ODD CHR INCL ORD DEC INTEGER PROC

Language features

Feature Supported Example Token
Booleans TRUE FALSE
Strings
"Hello world"
"
Print() Debugging WriteString
MultiLine Comments
(* A comment
*)
(* *)
Pointers
Comments
Semantic Indentation ϴ
Operator Overloading ϴ
Line Comments ϴ

Books about Modula-2 from ISBNdb

title authors year publisher
Programming in Modula-2 (Texts and monographs in computer science) Wirth, Niklaus 1985 Springer-Verlag
assembly-language.html · modula-2.html · dart.html

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