parser.cpp


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#include <cstdio>
#include <cctype>
#include <sstream>
#include "parser.h"
#include "exc.h"
#include "consts.h"
#include "builtin.h"

using std::stringstream;

static char buff[TOKEN_BUFF_SIZE];
static EvalObj *parse_stack[PARSE_STACK_SIZE];
extern Cons *empty_list;

Tokenizor::Tokenizor() : stream(stdin), buff_ptr(buff) {}
void Tokenizor::set_stream(FILE *_stream) {
    stream = _stream;
}

#define IS_BRACKET(ch) \
    ((ch) == '(' || (ch) == ')') 
#define IS_SPACE(ch) \
    ((ch) == ' ' || (ch) == '\t' || (ch) == '\n')
#define IS_DELIMITER(ch) \
    (IS_BRACKET(ch) || IS_SPACE(ch))
#define POP \
do { \
    *buff_ptr = 0; \
    ret = string(buff); \
    buff_ptr = buff; \
} while (0)

bool Tokenizor::get_token(string &ret) {
    char ch;
    bool flag = false;
    while (fread(&ch, 1, 1, stream))
    {
        if (buff_ptr != buff && 
            (IS_BRACKET(*buff) || IS_DELIMITER(ch)))
        {
            POP;
            flag = true;
        }
        if (!IS_SPACE(ch)) *buff_ptr++ = ch;
        if (flag) return true;
    }
    if (buff_ptr != buff) POP;
    return false; // can't read more 
}

ASTGenerator::ASTGenerator() {}
EvalObj *ASTGenerator::to_float(const string &str) {
    stringstream ss(str);
    double val;
    ss >> val;
    if (ss.fail() || !ss.eof()) return NULL;
    return new FloatObj(val);
}

EvalObj *ASTGenerator::to_int(const string &str) {
    stringstream ss(str);
    int val;
    ss >> val;
    if (ss.fail() || !ss.eof()) return NULL;
    return new IntObj(val);
}


EvalObj *ASTGenerator::to_obj(const string &str) {
    EvalObj *res = NULL;
    if ((res = ASTGenerator::to_int(str)))
        return res;
    if ((res = ASTGenerator::to_float(str)))
        return res;
    return new SymObj(str);
}
Cons *ASTGenerator::absorb(Tokenizor *tk) {
    EvalObj **top_ptr = parse_stack;
    for (;;)
    {
        if (top_ptr > parse_stack && *parse_stack)
            return new Cons(*(top_ptr - 1), empty_list);
        string token;
        if (!tk->get_token(token)) return NULL;
        if (token == "(")
            *top_ptr++ = NULL;  // Make the beginning of a new level
        else if (token == ")")
        {
            Cons *lst = empty_list;
            while (top_ptr >= parse_stack && *(--top_ptr))
                lst = new Cons(*top_ptr, lst); // Collect the list
            if (top_ptr < parse_stack)
                throw NormalError(READ_ERR_UNEXPECTED_RIGHT_BRACKET);
            *top_ptr++ = lst;
        }
        else *top_ptr++ = ASTGenerator::to_obj(token);
    }
}