147 lines
2.5 KiB
C
147 lines
2.5 KiB
C
/*
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E ::= T{+T}
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T ::= F{*F}
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F ::= (E)|i
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdbool.h>
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#include <ctype.h>
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#define eprintf(...) fprintf(stderr, __VA_ARGS__)
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typedef enum TokenType {
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INTEGER = 1,
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PLUS = 2,
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MULT = 4,
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LBRACE = 8,
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RBRACE = 16,
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LF = 32,
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EF = 64,
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} TokenType;
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typedef struct _Token {
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TokenType type;
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int value;
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} Token;
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void fatal(const char* message);
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Token scan();
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int e();
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int t();
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int f();
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static Token current;
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int main(int argc, char* argv[]) {
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current = scan();
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int result = e();
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printf("Success, result: %d\n", result);
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return 0;
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}
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Token scan() {
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static char prev_s = 0;
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Token token = {0, 0};
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char s;
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if (prev_s) {
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s = prev_s;
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prev_s = 0;
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}
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else {
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s = getchar();
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}
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while (isblank(s)) s = getchar();
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while (s >= '0' && s <= '9') {
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token.type = INTEGER;
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token.value = token.value * 10 + ((int) (s - '0'));
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s = getchar();
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}
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if (token.type == INTEGER) {
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prev_s = s;
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return token;
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}
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switch (s) {
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case '+': token.type = PLUS; break;
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case '*': token.type = MULT; break;
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case '(': token.type = LBRACE; break;
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case ')': token.type = RBRACE; break;
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case '\n':
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case '\r':
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case '\f':
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token.type = LF; break;
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case EOF: token.type = EF; break;
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default:
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eprintf("'%c' (%d)\n", s, s);
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fatal("Unexpected symbol");
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break;
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}
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return token;
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}
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int e() {
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int result = t();
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while (current.type == PLUS) {
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current = scan();
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result += t();
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}
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return result;
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}
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int t() {
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int result = f();
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while (current.type == MULT) {
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current = scan();
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result *= f();
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}
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return result;
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}
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int f() {
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int result = 0;
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if (current.type == LBRACE) {
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current = scan();
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result = e();
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if (current.type != RBRACE) {
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fatal("Expected closing parentheses");
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}
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}
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else if (current.type == INTEGER) {
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result = current.value;
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}
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else if (current.type == LF) {
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fatal("Unexpected line feed");
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}
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else if (current.type == EF) {
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fatal("Unexpected EOF");
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}
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else {
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fatal("Unexpected token");
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}
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current = scan();
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return result;
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}
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void fatal(const char* message) {
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eprintf("Error: %s\n", message);
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exit(1);
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}
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