1 files changed, 94 insertions, 0 deletions
diff --git a/parser.cpp b/parser.cpp
new file mode 100644
index 0000000..0143700
--- /dev/null
+++ b/parser.cpp
@@ -0,0 +1,94 @@
+#include <cstdio>
+#include <cctype>
+#include <sstream>
+#include "parser.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;
+        tk->get_token(token); 
+        if (token == "(")
+            *top_ptr++ = NULL;  // Make the beginning of a new level
+        else if (token == ")")
+        {
+            Cons *lst = empty_list;
+            while (*(--top_ptr))
+                lst = new Cons(*top_ptr, lst); // Collect the list
+            *top_ptr++ = lst;
+        }
+        else *top_ptr++ = ASTGenerator::to_obj(token);
+    }
+}