%start program

 /* SEMANTIC RECORD */
 /* char *id: For returning identifiers */
 /*
Place to easily pasting/cutting the union declaration
 */

%union {
char *id;
}

/* Simple identifier */
 /*
Place to exchange the IDENTIFIER token declarations
 */
%token IDENTIFIER
%type <id> IDENTIFIER

%token LET IN
/* "integer" keyword */
/* both INT e INTEGER exist? Removed INT, occurrences changed.
%token INT
*/
%token INTEGER

/* Same question for NUMBER: should it exist?
   Replaced all of its occurrences with INTEGER
   -> wrong, written numbers X 'integer' keyword. Changes undone
*/
%token NUMBER

 /* FI was missing */
%token SKIP IF THEN ELSE FI END WHILE DO READ WRITE
     /* ASSGNOP was missing */
%token ASSGNOP 
%left '-' '+'
%left '*' '/'
%left '<' '>' '=' '' /* these where missing on the book, added */
%right '^ '

%{

#include <stdlib.h> /* For malloc in symbol table */
#include <string.h> /* For strcmp in symbol table */
#include <stdio.h> /* For error messages */
#include "st.h" /* The Symbol Table Module */

/* Redeclaration? Should not be #define YYDEBUG 1 / * for debugging / para depuração */

/*  Global variable 'Errors' to substitute the previously
  undeclared variable 'errors' */
  int Errors = 0;

int yyerror (char *s);     // function header, removes a warning 
int install( char* sym_name)
{
    symrec *s;
    s = getsym(sym_name);
    if (s == 0)
	s = putsym (sym_name);
    else
    {
	Errors++;
	printf("%s is already defined\n", sym_name);
	return 0;
    }
    return 1;
}

int context_check(char* sym_name)
{
    if ( getsym( sym_name ) == 0 )
    {
	printf("%s is an undeclared identifier\n", sym_name);
	return 0;
    }
    return 1;
}


%}

%%

 /* Grammar rules and actions */

program : LET declarations IN commands END ;

declarations : /* empty */
    | INTEGER id_seq IDENTIFIER '.' { install( $3 ); }
;

id_seq : /* empty */
    | id_seq IDENTIFIER ','	    { install( $2 ); }
;
commands : /* empty */
    | commands command ';'
;
command : SKIP
    | READ IDENTIFIER		    { context_check( $2 ); }
    | WRITE exp
    | IDENTIFIER ASSGNOP exp	    { context_check( $1 ); }
    | IF exp THEN commands ELSE commands FI
    | WHILE exp DO commands END
;
 /* expressions */
exp : NUMBER
				    /* in book it is $2, wrong */
   | IDENTIFIER			    { context_check( $1 ); }
   | exp '<' exp
   | exp '=' exp
   | exp '>' exp
   | exp '+' exp
   | exp '-' exp
   | exp '' exp
   | exp '/' exp
   | exp '^ ' exp
   | '(' exp ')'
;

%%

 /* C subroutines */

/* não tem saída, a árvore de reconhec. fica implícita */
/* no output, implicit parse tree */
int main( int argc, char *argv[] )
{
    extern FILE *yyin;
    ++argv; --argc;
    yyin = fopen( argv[0], "r" );
    // yydebug = 1;           // line commented -> bad fix

    // errors = 0;            // initialization unneeded => line removed 
    yyparse ();
    return 0;
}
int yyerror (char *s) /* called by yyparse() in error situations */
{
    printf ("%s\n", s);
    return 0;
}