tokenize.c

#include "chibi.h"

char *user_input;
Token *token;

// Reports an error and exit.
void error(char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  exit(1);
}

// Reports an error location and exit.
static void verror_at(char *loc, char *fmt, va_list ap) {

  int pos = loc - user_input;
  fprintf(stderr, "%s\n", user_input);
  fprintf(stderr, "%*s", pos, ""); // print pos spaces.
  fprintf(stderr, "^ ");
  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  exit(1);
}
// Reports an error location and exit.
void error_at(char *loc, char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  verror_at(loc, fmt, ap);
}

// Reports an error location and exit.
void error_tok(Token *tok, char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  verror_at(tok->str, fmt, ap);
}

// Consumes the current token if it matches `op`.
Token *consume(char *op) {
  if (token->kind != TK_RESERVED || strlen(op) != token->len ||
      strncmp(token->str, op, token->len))
    return NULL;
  Token *t = token;
  token = token->next;
  return t;
}
// Returns true if the current token matches a given string.
Token *peek(char *s) {
    if (token->kind != TK_RESERVED || strlen(s) != token->len ||
        strncmp(token->str, s, token->len))
        return NULL;
    return token;
}


// Ensure that the current token is `op`.
void expect(char *s) {
  if (!peek(s))
    error_tok(token, "expected \"%s\"", s);
  token = token->next;
}

Token *consume_ident(void) {
    if (token->kind != TK_IDENT)
        return NULL;
    Token *t = token;
    token = token->next;
    return t;
}

// Ensure that the current token is TK_NUM.
long expect_number(void) {
  if (token->kind != TK_NUM)
    error_tok(token, "expected a number");
  long val = token->val;
  token = token->next;
  return val;
}

bool at_eof(void) {
  return token->kind == TK_EOF;
}

// Ensure that the current token is TK_IDENT.
char *expect_ident(void) {
    if (token->kind != TK_IDENT)
        error_tok(token, "expected an identifier");
    char *s = strndup(token->str, token->len);
    token = token->next;
    return s;
}

// Create a new token and add it as the next token of `cur`.
static Token *new_token(TokenKind kind, Token *cur, char *str, int len) {
  Token *tok = calloc(1, sizeof(Token));
  tok->kind = kind;
  tok->str = str;
  tok->len = len;
  cur->next = tok;
  return tok;
}

static bool startswith(char *p, char *q) {
  return strncmp(p, q, strlen(q)) == 0;
}

static bool is_alpha(char c) {
  return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_';
}

static bool is_alnum(char c) {
  return is_alpha(c) || ('0' <= c && c <= '9');
}

static char *starts_with_reserved(char *p) {
  // Keyword
  static char *kw[] = {"return", "if", "else", "while", "for", "int", "sizeof"};

  for (int i = 0; i < sizeof(kw) / sizeof(*kw); i++) {
    int len = strlen(kw[i]);
    if (startswith(p, kw[i]) && !is_alnum(p[len]))
      return kw[i];
  }

  // Multi-letter punctuator
  static char *ops[] = {"==", "!=", "<=", ">="};

  for (int i = 0; i < sizeof(ops) / sizeof(*ops); i++)
    if (startswith(p, ops[i]))
      return ops[i];

  return NULL;
}

// Tokenize `user_input` and returns new tokens.
Token *tokenize(void) {
  char *p = user_input;
  Token head = {};
  Token *cur = &head;

  while (*p) {
    // Skip whitespace characters.
    if (isspace(*p)) {
      p++;
      continue;
    }

    // Keywords or multi-letter punctuators
    char *kw = starts_with_reserved(p);
    if (kw) {
      int len = strlen(kw);
      cur = new_token(TK_RESERVED, cur, p, len);
      p += len;
      continue;
    }

    // Identifier
    if (is_alpha(*p)) {
        char *q = p++;
        while (is_alnum(*p))
            p++;
        cur = new_token(TK_IDENT, cur, q, p - q);
        continue;
    }

    // Single-letter punctuators
    if (ispunct(*p)) {
      cur = new_token(TK_RESERVED, cur, p++, 1);
      continue;
    }

    // Integer literal
    if (isdigit(*p)) {
      cur = new_token(TK_NUM, cur, p, 0);
      char *q = p;
      cur->val = strtol(p, &p, 10);
      cur->len = p - q;
      continue;
    }

    error_at(p, "invalid token");
  }

  new_token(TK_EOF, cur, p, 0);
  return head.next;
}