PL0编译器实现：从源码到PCODE解析

program   PL0   (input,output); 
(*PL/0   compiler   with   code   generation*) 
(*Program   5.6   in   Algorithms   +   Data   Structures   =   Programs*) 
(*Almost   identical   with   the   version   in   Compilerbau   *) 
label   
    99; 
const 
    norw   =   11;             (*no.   of   reserved   words*) 
    txmax   =   100;         (*length   of   identifier   table*) 
    nmax   =   14;             (*max.   no.   of   digits   in   numbers*) 
    al   =   10;                 (*length   of   identifiers*) 
    amax   =   2047;         (*maximum   address*) 
    levmax   =   3;           (*maximum   depth   of   block   nesting*) 
    cxmax   =   200;         (*size   of   code   array*) 

type 
    symbol   =   (nul,ident,number,plus,minus,times,slash,oddsym, 
                        eql,neq,lss,leq,gtr,geq,lparen,rparen,comma,semicolon, 
                        period,becomes,beginsym,endsym,ifsym,thensym, 
                        whilesym,dosym,callsym,constsym,varsym,procsym); 
    alfa   =         packed   array[1..al]   of   char; 
    object_1   =   (constant,variable,prozedure);
    symset   =   set   of   symbol; 
    fct   =         (lit,opr,lod,sto,cal,int,jmp,jpc);       (*functions*) 
    instruction   =   
        packed   record 
            f:   fct;             (*function   code*) 
            l:   0..levmax;(*level*) 
            a:   0..amax;     (*displacement   address*) 
        end; 

(* 
    lit   0,a:   load   constant   a 
    opr   0,a:   execute   operation   a 
    lod   l,a:   load   variable   l,a 
    sto   l,a:   store   variable   l,a 
    cal   l,a:   call   procedure   a   at   level   l 
    int   0,a:   increment   t-register   by   a 
    jmp   0,a:   jump   to   a 
    jpc   0,a:   jump   conditional   to   a*) 

var 
    ch:   char;         (*last   character   read*) 
    sym:   symbol;   (*last   symbol   read*) 
    id:   alfa;         (*last   identifier   read*) 
    num:   integer;(*last   number   read*) 
    cc:   integer;   (*character   count*) 
    ll:   integer;   (*line   length*) 
    kk,err:   integer; 
    cx:   integer;   (*code   allocation   index*) 
    line:   array[1..81]   of   char; 
    a:   alfa; 
    code:   array[0..cxmax]   of   instruction; 
    word:   array[1..norw]   of   alfa; 
    wsym:   array[1..norw]   of   symbol; 
    ssym:   array[char]   of   symbol; 
    mnemonic:   array[fct]   of   
                            packed   array[1..5]   of   char; 
    declbegsys,statbegsys,facbegsys:   symset; 
    table:   
        array[0..txmax]   of