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#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
/// scanner
// constants
enum {
MAX_IDENT_LEN = 10
};
// token types
typedef enum {
S_undef,
S_token,
S_number,
S_identifier,
S_false,
S_true,
S_eof
} Sym;
typedef struct {
Sym sym;
union {
char s[MAX_IDENT_LEN];
int n;
bool b;
};
int tag;
} Symbol;
char *symbol_tostr( Symbol s, char *buf, size_t buflen )
{
switch( s.sym ) {
case S_undef:
snprintf( buf, buflen, "UNDEF" );
break;
case S_token:
if( isprint( s.tag ) ) {
snprintf( buf, buflen, "TOK(%c)", s.tag );
} else {
snprintf( buf, buflen, "TOK(0x%dx)", s.tag );
}
break;
case S_number:
snprintf( buf, buflen, "NUMBER(%d)", s.n );
break;
case S_identifier:
snprintf( buf, buflen, "IDENT(%s)", s.s );
break;
case S_eof:
snprintf( buf, buflen, "EOF" );
break;
default:
snprintf( buf, buflen, "ILLEGAL(%d)", s.sym );
}
return buf;
}
typedef struct {
int peek;
int row;
int col;
FILE *f;
Symbol s;
} Scanner;
void scanner_init( Scanner *s, FILE *f )
{
s->peek = ' ';
s->row = 1;
s->col = 1;
s->f = f;
s->s.sym = S_undef;
}
void scanner_skip_whitespace( Scanner *s )
{
for( ; ; s->peek = getc( s->f ) ) {
s->col++;
if( s->peek == ' ' || s->peek == '\t' ) {
continue;
} else if( s->peek == '\n' ) {
s->row++;
s->col = 1;
} else if( s->peek == EOF ) {
break;
} else {
break;
}
}
}
Symbol scanner_get_int( Scanner *s )
{
Symbol sym;
sym.sym = S_number;
sym.n = 0;
do {
sym.n = sym.n * 10 + ( s->peek - '0' );
s->peek = getc( s->f );
} while( isdigit( s->peek ) && ( s->peek != EOF ) );
return sym;
}
Symbol scanner_scan( Scanner *s )
{
Symbol sym;
if( s->peek == EOF ) {
sym.sym = S_eof;
return sym;
}
scanner_skip_whitespace( s );
if( isdigit( s->peek ) ) {
sym = scanner_get_int( s );
return sym;
}
sym.sym = S_token;
sym.tag = s->peek;
s->peek = ' ';
return sym;
}
/// parser
typedef struct {
Scanner *s;
} Parser;
void parser_init( Parser *p, Scanner *s )
{
p->s = s;
}
void parser_error( Parser *p, const char *s, Symbol sym )
{
char errbuf[255];
fprintf( stderr, "\nERR: %s at symbol '%s' at line %d, column %d\n",
s, symbol_tostr( sym, errbuf, 255 ), p->s->row, p->s->col );
exit( 1 );
}
void parser_term( Parser *p )
{
Symbol s = scanner_scan( p->s );
if( s.sym == S_number ) {
printf( "%d ", s.n );
} else {
parser_error( p, "expecting number", s );
}
}
void parser_rest( Parser *p )
{
Symbol s = scanner_scan( p->s );
if( s.sym == S_token ) {
switch( s.tag ) {
case '+':
parser_term( p );
putchar( '+' ); putchar( ' ' );
parser_rest( p );
break;
case '-':
parser_term( p );
putchar( '-' ); putchar( ' ' );
parser_rest( p );
break;
default:
parser_error( p, "expecting operator '+' or '-'", s );
}
} else if( s.sym == S_eof ) {
return;
} else {
parser_error( p, "expecting an operator '+' or '-'", s );
}
}
void parser_expr( Parser *p )
{
parser_term( p );
parser_rest( p );
}
void parser_parse( Parser *p )
{
parser_expr( p );
}
/// main
int main( void )
{
Scanner s;
Parser p;
scanner_init( &s, stdin );
parser_init( &p, &s );
parser_parse( &p );
puts( "" );
exit( 0 );
}
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