new ext_repr() approach

7 files changed, 225 insertions, 92 deletions

diff --git a/Makefile b/Makefile
index 3a3f37a..07feba0 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ main: main.o parser.o builtin.o model.o eval.o exc.o consts.o
 	g++ -o main $^ -pg -lgmp
 
 .cpp.o:
-	g++ $< -c -g -pg -DDEBUG -DGMP_SUPPORT
+	g++ $< -c -g -pg -DGMP_SUPPORT
 
 clean:
 	rm -f *.o
diff --git a/builtin.cpp b/builtin.cpp
index 6579e98..adf069d 100644
--- a/builtin.cpp
+++ b/builtin.cpp
@@ -35,7 +35,7 @@ bool is_list(Pair *ptr) {
     if (ptr == empty_list) return true;
     EvalObj *nptr; 
     for (;;) 
-        if ((nptr = ptr->cdr)->is_cons_obj()) 
+        if ((nptr = ptr->cdr)->is_pair_obj()) 
             ptr = TO_PAIR(nptr); 
         else break; 
     return ptr->cdr == empty_list;
@@ -227,8 +227,8 @@ bool CompNumObj::eq(NumObj *_r) {
 }
 
 
-string CompNumObj::ext_repr() {
-    return double_to_str(real) + double_to_str(imag, true) + "i";
+ReprCons *CompNumObj::get_repr_cons() {
+    return new ReprStr(double_to_str(real) + double_to_str(imag, true) + "i");
 }
 
 #undef A
@@ -299,8 +299,8 @@ bool RealNumObj::gt(NumObj *_r) {
     return real > static_cast<RealNumObj*>(_r)->real;
 }
 
-string RealNumObj::ext_repr() {
-    return double_to_str(real);
+ReprCons *RealNumObj::get_repr_cons() {
+    return new ReprStr(double_to_str(real));
 }
 
 ExactNumObj::ExactNumObj(NumLvl level) : NumObj(level, true) {}
@@ -448,11 +448,11 @@ bool RatNumObj::eq(NumObj *_r) {
 #endif
 }
 
-string RatNumObj::ext_repr() {
+ReprCons *RatNumObj::get_repr_cons() {
 #ifndef GMP_SUPPORT
-    return int_to_str(A) + "/" + int_to_str(B);
+    return new ReprStr(int_to_str(A) + "/" + int_to_str(B));
 #else
-    return val.get_str();
+    return new ReprStr(val.get_str());
 #endif
 }
 
@@ -529,11 +529,11 @@ bool IntNumObj::eq(NumObj *_r) {
     return val == static_cast<IntNumObj*>(_r)->val;
 }
 
-string IntNumObj::ext_repr() {
+ReprCons *IntNumObj::get_repr_cons() {
 #ifndef GMP_SUPPORT
-    return int_to_str(val);
+    return new ReprStr(int_to_str(val));
 #else
-    return val.get_str();
+    return new ReprStr(val.get_str());
 #endif
 }
 
@@ -544,7 +544,7 @@ void SpecialOptIf::prepare(Pair *pc) {
         throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS)
     state = 0;  // Prepared
 
-    if (pc->cdr->is_cons_obj())
+    if (pc->cdr->is_pair_obj())
         pc = TO_PAIR(pc->cdr);
     else 
         IF_EXP_ERR;
@@ -553,7 +553,7 @@ void SpecialOptIf::prepare(Pair *pc) {
 
     pc->skip = false;
 
-    if (pc->cdr->is_cons_obj())
+    if (pc->cdr->is_pair_obj())
         pc = TO_PAIR(pc->cdr);
     else
         IF_EXP_ERR;
@@ -563,7 +563,7 @@ void SpecialOptIf::prepare(Pair *pc) {
     pc->skip = true;
     if (pc->cdr != empty_list)
     {
-        if (pc->cdr->is_cons_obj())
+        if (pc->cdr->is_pair_obj())
         {
             TO_PAIR(pc->cdr)->skip = true;
             if (TO_PAIR(pc->cdr)->cdr != empty_list)
@@ -624,7 +624,9 @@ Pair *SpecialOptIf::call(ArgList *args, Environment * &envt,
     }
 }
 
-string SpecialOptIf::ext_repr() { return string("#<Builtin Macro: if>"); }
+ReprCons *SpecialOptIf::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: if>"); 
+}
 
 SpecialOptLambda::SpecialOptLambda() : SpecialOptObj("lambda") {}
 #define FILL_MARKS(pc, flag)  \
@@ -634,7 +636,7 @@ do  \
     Pair *ptr; \
     for (ptr = pc;;)  \
     { \
-        if ((nptr = ptr->cdr)->is_cons_obj()) \
+        if ((nptr = ptr->cdr)->is_pair_obj()) \
             ptr = TO_PAIR(nptr); \
         else break; \
         ptr->skip = flag; \
@@ -659,7 +661,7 @@ do  \
     Pair *ptr; \
     for (ptr = TO_PAIR(p);;)  \
     { \
-        if ((nptr = ptr->cdr)->is_cons_obj()) \
+        if ((nptr = ptr->cdr)->is_pair_obj()) \
             ptr = TO_PAIR(nptr); \
         else break; \
         CHECK_SYMBOL(ptr->car); \
@@ -706,18 +708,20 @@ Pair *SpecialOptLambda::call(ArgList *args, Environment * &envt,
     return ret_addr->next;  // Move to the next instruction
 }
 
-string SpecialOptLambda::ext_repr() { return string("#<Builtin Macro: lambda>"); }
+ReprCons *SpecialOptLambda::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: lambda>"); 
+}
 
 SpecialOptDefine::SpecialOptDefine() : SpecialOptObj("define") {}
 
 void SpecialOptDefine::prepare(Pair *pc) {
-    if (!pc->cdr->is_cons_obj())
+    if (!pc->cdr->is_pair_obj())
         throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS);
 
     if (TO_PAIR(pc->cdr)->car->is_simple_obj())  // Simple value assignment
     {
         pc = TO_PAIR(pc->cdr);
-        if (!pc->cdr->is_cons_obj())
+        if (!pc->cdr->is_pair_obj())
             throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS);
         pc->skip = true;           // Skip the identifier
         TO_PAIR(pc->cdr)->skip = false; 
@@ -773,17 +777,19 @@ Pair *SpecialOptDefine::call(ArgList *args, Environment * &envt,
     return ret_addr->next;
 }
 
-string SpecialOptDefine::ext_repr() { return string("#<Builtin Macro: define>"); }
+ReprCons *SpecialOptDefine::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: define>"); 
+}
 
 void SpecialOptSet::prepare(Pair *pc) {
-    if (!pc->cdr->is_cons_obj())
+    if (!pc->cdr->is_pair_obj())
         throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS);
 
     pc = TO_PAIR(pc->cdr);
 
     pc->skip = true;       // Skip the identifier
 
-    if (!pc->cdr->is_cons_obj())
+    if (!pc->cdr->is_pair_obj())
         throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS);
 
     pc = TO_PAIR(pc->cdr);
@@ -811,7 +817,9 @@ Pair *SpecialOptSet::call(ArgList *args, Environment * &envt,
 
 SpecialOptSet::SpecialOptSet() : SpecialOptObj("set!") {}
 
-string SpecialOptSet::ext_repr() { return string("#<Builtin Macro: set!>"); }
+ReprCons *SpecialOptSet::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: set!>"); 
+}
 
 SpecialOptQuote::SpecialOptQuote() : SpecialOptObj("quote") {}
 
@@ -830,7 +838,9 @@ Pair *SpecialOptQuote::call(ArgList *args, Environment * &envt,
     return ret_addr->next;
 }
 
-string SpecialOptQuote::ext_repr() { return string("#<Builtin Macro: quote>"); }
+ReprCons *SpecialOptQuote::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: quote>"); 
+}
 
 SpecialOptEval::SpecialOptEval() : SpecialOptObj("eval") {}
 
@@ -858,7 +868,9 @@ Pair *SpecialOptEval::call(ArgList *args, Environment * &envt,
     }
 }
 
-string SpecialOptEval::ext_repr() { return string("#<Builtin Macro: eval>"); }
+ReprCons *SpecialOptEval::get_repr_cons() { 
+    return new ReprStr("#<Builtin Macro: eval>"); 
+}
 
 BUILTIN_PROC_DEF(make_pair) {
     ARGS_EXACTLY_TWO;
@@ -867,7 +879,7 @@ BUILTIN_PROC_DEF(make_pair) {
 
 BUILTIN_PROC_DEF(pair_car) {
     ARGS_EXACTLY_ONE;
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
 
     return TO_PAIR(args->car)->car;
@@ -875,7 +887,7 @@ BUILTIN_PROC_DEF(pair_car) {
 
 BUILTIN_PROC_DEF(pair_cdr) {
     ARGS_EXACTLY_ONE;
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
 
     return TO_PAIR(args->car)->cdr;
@@ -1054,12 +1066,12 @@ BUILTIN_PROC_DEF(is_boolean) {
 
 BUILTIN_PROC_DEF(is_pair) {
     ARGS_EXACTLY_ONE;
-    return new BoolObj(args->car->is_cons_obj());
+    return new BoolObj(args->car->is_pair_obj());
 }
 
 BUILTIN_PROC_DEF(pair_set_car) {
     ARGS_EXACTLY_TWO;
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
     TO_PAIR(args->car)->car = TO_PAIR(args->cdr)->car;
     return new UnspecObj();
@@ -1067,7 +1079,7 @@ BUILTIN_PROC_DEF(pair_set_car) {
 
 BUILTIN_PROC_DEF(pair_set_cdr) {
     ARGS_EXACTLY_TWO;
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
     TO_PAIR(args->car)->cdr = TO_PAIR(args->cdr)->car;
     return new UnspecObj();
@@ -1082,13 +1094,13 @@ BUILTIN_PROC_DEF(is_list) {
     ARGS_EXACTLY_ONE;
     if (args->car == empty_list)
         return new BoolObj(true);
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         return new BoolObj(false);
     args = TO_PAIR(args->car);
     EvalObj *nptr;
     for (;;)
     {
-        if ((nptr = args->cdr)->is_cons_obj())
+        if ((nptr = args->cdr)->is_pair_obj())
             args = TO_PAIR(nptr);
         else break;
     }
@@ -1113,14 +1125,14 @@ BUILTIN_PROC_DEF(length) {
     ARGS_EXACTLY_ONE;
     if (args->car == empty_list)
         return new IntNumObj(mpz_class(0));
-    if (!args->car->is_cons_obj())
+    if (!args->car->is_pair_obj())
         throw TokenError("a list", RUN_ERR_WRONG_TYPE);
     int num = 0;
     EvalObj *nptr;
     for (args = TO_PAIR(args->car);;)
     {
         num++;
-        if ((nptr = args->cdr)->is_cons_obj())
+        if ((nptr = args->cdr)->is_pair_obj())
             args = TO_PAIR(nptr);
         else 
             break;
@@ -1140,7 +1152,7 @@ Pair *copy_list(Pair *src, EvalObj * &tail) {
     {
         TO_PAIR(tail)->cdr = new Pair(*src);
         tail = TO_PAIR(TO_PAIR(tail)->cdr);
-        if ((nptr = src->cdr)->is_cons_obj())
+        if ((nptr = src->cdr)->is_pair_obj())
             src = TO_PAIR(nptr);
         else break;
     }
@@ -1154,18 +1166,18 @@ BUILTIN_PROC_DEF(append) {
         if (tail == empty_list)
         {
             head = args->car;
-            if (head->is_cons_obj())
+            if (head->is_pair_obj())
                 head = copy_list(TO_PAIR(head), tail);
             else tail = head;
         }
         else 
         {
-            if (tail->is_cons_obj())
+            if (tail->is_pair_obj())
             {
                 Pair *prev = TO_PAIR(tail);
                 if (prev->cdr != empty_list)
                     throw TokenError("empty list", RUN_ERR_WRONG_TYPE);
-                if (args->car->is_cons_obj())
+                if (args->car->is_pair_obj())
                     prev->cdr = copy_list(TO_PAIR(args->car), tail);
                 else
                     prev->cdr = args->car;
@@ -1182,7 +1194,7 @@ BUILTIN_PROC_DEF(reverse) {
     Pair *tail = empty_list;
     EvalObj *ptr;
     for (ptr = args->car; 
-            ptr->is_cons_obj(); ptr = TO_PAIR(ptr)->cdr)
+            ptr->is_pair_obj(); ptr = TO_PAIR(ptr)->cdr)
         tail = new Pair(TO_PAIR(ptr)->car, tail);
     if (ptr != empty_list)
         throw TokenError("a list", RUN_ERR_WRONG_TYPE);
@@ -1200,12 +1212,12 @@ BUILTIN_PROC_DEF(list_tail) {
         throw TokenError("a non-negative integer", RUN_ERR_WRONG_TYPE);
     EvalObj *ptr;
     for (i = 0, ptr = args->car;
-            ptr->is_cons_obj(); ptr = TO_PAIR(ptr)->cdr, i++)
+            ptr->is_pair_obj(); ptr = TO_PAIR(ptr)->cdr, i++)
         if (i == k) break;
     if (i != k)
         throw TokenError("a pair", RUN_ERR_WRONG_TYPE);
     EvalObj *tail;
-    if (ptr->is_cons_obj())
+    if (ptr->is_pair_obj())
         return copy_list(TO_PAIR(ptr), tail);
     else
         return ptr;
diff --git a/builtin.h b/builtin.h
index 589e7a9..2633ed8 100644
--- a/builtin.h
+++ b/builtin.h
@@ -40,7 +40,7 @@ class CompNumObj: public InexactNumObj {
         bool lt(NumObj *r);
         bool gt(NumObj *r);
         bool eq(NumObj *r);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class RealNumObj
@@ -65,7 +65,7 @@ class RealNumObj: public InexactNumObj {
         bool lt(NumObj *r);
         bool gt(NumObj *r);
         bool eq(NumObj *r);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 
 };
 
@@ -105,7 +105,7 @@ class RatNumObj: public ExactNumObj {
         bool lt(NumObj *r);
         bool gt(NumObj *r);
         bool eq(NumObj *r);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class IntNumObj
@@ -138,7 +138,7 @@ class IntNumObj: public ExactNumObj {
         bool lt(NumObj *r);
         bool gt(NumObj *r);
         bool eq(NumObj *r);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 
@@ -165,7 +165,7 @@ class SpecialOptIf: public SpecialOptObj {
         void prepare(Pair *pc);
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptLambda
@@ -178,7 +178,7 @@ class SpecialOptLambda: public SpecialOptObj {
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
 
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptDefine
@@ -190,7 +190,7 @@ class SpecialOptDefine: public SpecialOptObj {
         void prepare(Pair *pc);
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptSet
@@ -202,7 +202,7 @@ class SpecialOptSet: public SpecialOptObj {
         void prepare(Pair *pc);
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptLambda
@@ -215,7 +215,7 @@ class SpecialOptQuote: public SpecialOptObj {
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
 
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptEval
@@ -230,7 +230,7 @@ class SpecialOptEval: public SpecialOptObj {
         Pair *call(ArgList *args, Environment * &envt, 
                     Continuation * &cont, FrameObj ** &top_ptr);
 
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 #define BUILTIN_PROC_DEF(func)\
diff --git a/main.cpp b/main.cpp
index 810537d..db635e8 100644
--- a/main.cpp
+++ b/main.cpp
@@ -5,12 +5,8 @@
 #include "exc.h"
 #include <cstdio>
 
-#ifdef DEBUG
-extern Pair *empty_list;
-#endif
-
 int main() {
-    //freopen("in.scm", "r", stdin);
+    freopen("in.scm", "r", stdin);
     Tokenizor *tk = new Tokenizor();
     ASTGenerator *ast = new ASTGenerator();
     Evaluator *eval = new Evaluator();
diff --git a/model.cpp b/model.cpp
index b652d47..4502577 100644
--- a/model.cpp
+++ b/model.cpp
@@ -3,13 +3,15 @@
 #include "exc.h"
 #include "consts.h"
 
+static ReprCons *repr_stack[REPR_STACK_SIZE];
+
 FrameObj::FrameObj(ClassType _ftype) : ftype(_ftype) {}
 
 EmptyList *empty_list = new EmptyList();
 
 EmptyList::EmptyList() : Pair(NULL, NULL) {}
 
-string EmptyList::ext_repr() { return string("()"); }
+ReprCons *EmptyList::get_repr_cons() { return new ReprStr("()"); }
 
 bool FrameObj::is_ret_addr() { 
     return ftype & CLS_RET_ADDR;
@@ -35,7 +37,7 @@ bool EvalObj::is_opt_obj() {
     return otype & CLS_OPT_OBJ;
 }
 
-bool EvalObj::is_cons_obj() {
+bool EvalObj::is_pair_obj() {
     return this != empty_list && (otype & CLS_CONS_OBJ);
 }
 
@@ -57,12 +59,40 @@ bool EvalObj::is_true() {
 }
 
 string EvalObj::ext_repr() {
+    ReprCons **top_ptr = repr_stack; 
+    *top_ptr++ = this->get_repr_cons();
+    //printf("%s\n", (this->get_repr_cons())->repr.c_str());
+    EvalObj *obj;
+    while (!(*repr_stack)->done)
+    {
+        if ((*(top_ptr - 1))->done)
+        {
+            top_ptr--;
+            obj = (*(top_ptr - 1))->next((*top_ptr)->repr + " ");
+            if (obj)
+                *top_ptr++ = obj->get_repr_cons();
+            else
+            {
+                *(top_ptr - 1) = new ReprStr((*(top_ptr - 1))->repr);
+            }
+        }
+        else
+        {
+            obj = (*(top_ptr - 1))->next("");
+            *top_ptr++ = obj->get_repr_cons();
+        }
+    }
+    return (*repr_stack)->repr;
 }
 
 Pair::Pair(EvalObj *_car, EvalObj *_cdr) : 
     EvalObj(CLS_CONS_OBJ), car(_car), cdr(_cdr), skip(false), 
     next(NULL) {}
 
+ReprCons *Pair::get_repr_cons() {
+    return new ListReprCons(this);
+}
+
 RetAddr::RetAddr(Pair *_addr) : FrameObj(CLS_RET_ADDR), addr(_addr) {}
 
 ParseBracket::ParseBracket(unsigned char _btype) : 
@@ -70,12 +100,16 @@ ParseBracket::ParseBracket(unsigned char _btype) :
 
 UnspecObj::UnspecObj() : EvalObj(CLS_SIM_OBJ) {}
 
-string UnspecObj::ext_repr() { return string("#<Unspecified>"); }
+ReprCons *UnspecObj::get_repr_cons() { 
+    return new ReprStr("#<Unspecified>");
+}
 
 SymObj::SymObj(const string &str) : 
     EvalObj(CLS_SIM_OBJ | CLS_SYM_OBJ), val(str) {}
 
-string SymObj::ext_repr() { return val; }
+ReprCons *SymObj::get_repr_cons() { 
+    return new ReprStr(val); 
+}
 
 OptObj::OptObj() : EvalObj(CLS_SIM_OBJ | CLS_OPT_OBJ) {}
 
@@ -95,7 +129,7 @@ Pair *ProcObj::call(ArgList *args, Environment * &genvt,
     // static_cast<SymObj*> because the params is already checked
     EvalObj *ppar, *nptr;
     for (ppar = params;
-            ppar->is_cons_obj(); 
+            ppar->is_pair_obj(); 
             ppar = TO_PAIR(ppar)->cdr)
     {
         if ((nptr = args->cdr) != empty_list)
@@ -115,7 +149,9 @@ Pair *ProcObj::call(ArgList *args, Environment * &genvt,
     return body;                    // Move pc to the proc entry point
 }
 
-string ProcObj::ext_repr() { return string("#<Procedure>"); }
+ReprCons *ProcObj::get_repr_cons() { 
+    return new ReprStr("#<Procedure>"); 
+}
 
 SpecialOptObj::SpecialOptObj(string _name) : OptObj(), name(_name) {}
 
@@ -123,7 +159,9 @@ BoolObj::BoolObj(bool _val) : EvalObj(CLS_SIM_OBJ | CLS_BOOL_OBJ), val(_val) {}
 
 bool BoolObj::is_true() { return val; }
 
-string BoolObj::ext_repr() { return string(val ? "#t" : "#f"); }
+ReprCons *BoolObj::get_repr_cons() { 
+    return new ReprStr(val ? "#t" : "#f"); 
+}
 
 BoolObj *BoolObj::from_string(string repr) {
     if (repr.length() != 2 || repr[0] != '#') 
@@ -142,7 +180,9 @@ bool NumObj::is_exact() { return exactness; }
 
 StrObj::StrObj(string _str) : EvalObj(CLS_SIM_OBJ | CLS_STR_OBJ), str(_str) {}
 
-string StrObj::ext_repr() { return str; }
+ReprCons *StrObj::get_repr_cons() { 
+    return new ReprStr(str); 
+}
 
 CharObj::CharObj(char _ch) : EvalObj(CLS_SIM_OBJ | CLS_CHAR_OBJ), ch(_ch) {}
 
@@ -157,16 +197,24 @@ CharObj *CharObj::from_string(string repr) {
     throw TokenError(char_name, RUN_ERR_UNKNOWN_CHAR_NAME);
 }
 
-string CharObj::ext_repr() {
+ReprCons *CharObj::get_repr_cons() {
     string val = "";
     if (ch == ' ') val = "space";
     else if (ch == '\n') val = "newline";
     else val += ch;
-    return "#\\" + val;
+    return new ReprStr("#\\" + val);
 }
 
 VecObj::VecObj() : EvalObj(CLS_SIM_OBJ | CLS_VECT_OBJ) {}
 
+EvalObj *VecObj::get_obj(int idx) {
+    return vec[idx];
+}
+
+int VecObj::get_size() { 
+    return vec.end() - vec.begin();
+}
+
 void VecObj::resize(int new_size) {
     vec.resize(new_size);
 }
@@ -175,6 +223,10 @@ void VecObj::push_back(EvalObj *new_elem) {
     vec.push_back(new_elem);
 }
 
+ReprCons *VecObj::get_repr_cons() {
+    return new VectReprCons(this);
+}
+
 StrObj *StrObj::from_string(string repr) {
     size_t len = repr.length();
     if (repr[0] == '\"' && repr[len - 1] == '\"')
@@ -193,8 +245,8 @@ Pair *BuiltinProcObj::call(ArgList *args, Environment * &envt,
     return ret_addr->next;          // Move to the next instruction
 }
 
-string BuiltinProcObj::ext_repr() { 
-    return "#<Builtin Procedure: " + name + ">";
+ReprCons *BuiltinProcObj::get_repr_cons() { 
+    return new ReprStr("#<Builtin Procedure: " + name + ">");
 }
 
 Environment::Environment(Environment *_prev_envt) : prev_envt(_prev_envt) {}
@@ -221,7 +273,50 @@ EvalObj *Environment::get_obj(EvalObj *obj) {
 }
 
 Continuation::Continuation(Environment *_envt, Pair *_pc, 
-                            Continuation *_prev_cont, 
-                            Pair *_proc_body) : 
-        envt(_envt), pc(_pc), prev_cont(_prev_cont), 
-        proc_body(_proc_body) {}
+        Continuation *_prev_cont, 
+        Pair *_proc_body) : 
+    envt(_envt), pc(_pc), prev_cont(_prev_cont), 
+    proc_body(_proc_body) {}
+
+ReprCons::ReprCons(bool _done) : done(_done) {}
+ReprStr::ReprStr(string _repr) : ReprCons(true) { repr = _repr; }
+EvalObj *ReprStr::next(const string &prev) {
+    throw NormalError(INT_ERR);
+}
+
+ListReprCons::ListReprCons(Pair *_ptr) : 
+    ReprCons(false), ptr(_ptr) { repr = "("; }
+
+EvalObj *ListReprCons::next(const string &prev) {
+    repr += prev;
+    EvalObj *res;
+    if (ptr->is_simple_obj())
+    {
+        repr += ". ";
+        res = ptr;
+        ptr = empty_list;
+        return res;
+    }
+    if (ptr == empty_list)
+    {
+        *repr.rbegin() = ')';
+        return NULL;
+    }
+
+    res = TO_PAIR(ptr)->car;
+    ptr = TO_PAIR(ptr)->cdr;
+    return res;
+}
+
+VectReprCons::VectReprCons(VecObj *_ptr) :
+    ReprCons(false), ptr(_ptr), idx(0) { repr = "#("; }
+
+EvalObj *VectReprCons::next(const string &prev) {
+    repr += prev;
+    if (idx == ptr->get_size())
+    {
+        *repr.rbegin() = ')';
+        return NULL;
+    }
+    else return ptr->get_obj(idx++);
+}
diff --git a/model.h b/model.h
index 32a1785..062a61d 100644
--- a/model.h
+++ b/model.h
@@ -18,6 +18,8 @@ typedef unsigned char NumLvl;
 const int CLS_RET_ADDR = 1 << 0;
 const int CLS_EVAL_OBJ = 1 << 1;
 const int CLS_PAR_BRA = 1 << 2;
+const int CLS_REPR_CONS = 1 << 3;
+const int CLS_REPR_STR = 1 << 4;
 
 const int CLS_SIM_OBJ = 1 << 0;
 const int CLS_CONS_OBJ = 1 << 1;
@@ -29,6 +31,7 @@ const int CLS_CHAR_OBJ = 1 << 6;
 const int CLS_STR_OBJ = 1 << 7;
 const int CLS_VECT_OBJ = 1 << 8;
 
+const int REPR_STACK_SIZE = 65536;
 
 #define TO_PAIR(ptr) \
     (static_cast<Pair*>(ptr))
@@ -65,6 +68,7 @@ class FrameObj {
 
 
 class Pair;
+class ReprCons;
 /** @class EvalObj
  * Objects that represents a value in evaluation
  */
@@ -93,7 +97,7 @@ class EvalObj : public FrameObj {
         /** Check if the object is an operator */
         bool is_opt_obj();
         /** Check if the object is a Pair */
-        bool is_cons_obj();
+        bool is_pair_obj();
         /** Check if the object is a number */
         bool is_num_obj();
         /** Check if the object is a boolean */
@@ -101,11 +105,13 @@ class EvalObj : public FrameObj {
         ClassType get_otype();
         virtual void prepare(Pair *pc);
         /** Any EvalObj has its external representation */
-        virtual string ext_repr();
+        string ext_repr();
         /** Always true for all EvalObjs except BoolObj */
         virtual bool is_true();         
+        virtual ReprCons *get_repr_cons() = 0;
 };
 
+class ListReprCons;
 /** @class Pair
  * Pair construct, which can be used to represent a list, or further
  * more, a syntax tree
@@ -119,6 +125,7 @@ class Pair : public EvalObj {
         Pair* next;                     /**< The next branch in effect */
 
         Pair(EvalObj *car, EvalObj *cdr);  /**< Create a Pair (car . cdr) */
+        ReprCons *get_repr_cons();
 };
 
 /** @class EmptyList
@@ -127,7 +134,7 @@ class Pair : public EvalObj {
 class EmptyList: public Pair {
     public:
         EmptyList();
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class RetAddr
@@ -141,13 +148,36 @@ class RetAddr : public FrameObj {
         RetAddr(Pair *addr);
 };
 
-class ReprConstructor : public FrameObj {
-    virtual EvalObj *next();
+class ReprCons {
+    public:
+        bool done;
+        string repr;
+        ReprCons(bool done); 
+        virtual EvalObj *next(const string &prev) = 0;
+};
+
+class ReprStr : public ReprCons {
+    public:
+        ReprStr(string repr);
+        EvalObj *next(const string &prev);
 };
 
-class ExtRepr : public FrameObj {
+class ListReprCons : public ReprCons {
+    private:
+        EvalObj *ptr;
     public:
-    string repr;
+        ListReprCons(Pair *ptr);
+        EvalObj *next(const string &prev);
+};
+
+class VecObj;
+class VectReprCons : public ReprCons {
+    private:
+        VecObj *ptr;
+        int idx;
+    public:
+        VectReprCons(VecObj *ptr);
+        EvalObj *next(const string &prev);
 };
 
 /** @class ParseBracket
@@ -166,7 +196,7 @@ class ParseBracket : public FrameObj {
 class UnspecObj: public EvalObj {
     public:
         UnspecObj();
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SymObj
@@ -177,10 +207,7 @@ class SymObj: public EvalObj {
         string val;
 
         SymObj(const string &);
-#ifdef DEBUG
-        string _debug_repr();
-#endif
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 // Everything is cons
@@ -222,7 +249,7 @@ class ProcObj: public OptObj {
         ProcObj(Pair *body, Environment *envt, EvalObj *params);
         Pair *call(ArgList *args, Environment * &envt,
                     Continuation * &cont, FrameObj ** &top_ptr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class SpecialOptObj
@@ -253,7 +280,7 @@ class BuiltinProcObj: public OptObj {
         BuiltinProcObj(BuiltinProc proc, string name);
         Pair *call(ArgList *args, Environment * &envt,
                     Continuation * &cont, FrameObj ** &top_ptr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class BoolObj
@@ -264,7 +291,7 @@ class BoolObj: public EvalObj {
         bool val;                       /**< true for \#t, false for \#f */ 
         BoolObj(bool);                  /**< Converts a C bool value to a BoolObj*/
         bool is_true();                 /**< Override EvalObj `is_true()` */
-        string ext_repr();
+        ReprCons *get_repr_cons();
         /** Try to construct an BoolObj object 
          * @return NULL if failed
          */
@@ -313,7 +340,7 @@ class StrObj: public EvalObj {
          * @return NULL if failed
          */
         static StrObj *from_string(string repr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 /** @class CharObj
@@ -329,7 +356,7 @@ class CharObj: public EvalObj {
          * @return NULL if failed
          */
         static CharObj *from_string(string repr);
-        string ext_repr();
+        ReprCons *get_repr_cons();
 };
 
 
@@ -344,10 +371,13 @@ class VecObj: public EvalObj {
     public:
         /** Construct a vector object */
         VecObj();
+        int get_size();
+        EvalObj *get_obj(int idx);
         /** Resize the vector */
         void resize(int new_size);
         /** Add a new element to the rear */
         void push_back(EvalObj *new_elem);
+        ReprCons *get_repr_cons();
 };
 
 typedef map<string, EvalObj*> Str2EvalObj;
diff --git a/parser.cpp b/parser.cpp
index b6486cc..ff21b7b 100644
--- a/parser.cpp
+++ b/parser.cpp
@@ -196,7 +196,7 @@ Pair *ASTGenerator::absorb(Tokenizor *tk) {
                 else
                 {
                     Pair *_lst = new Pair(obj, lst);    // Collect the list
-                    _lst->next = lst->is_cons_obj() ? TO_PAIR(lst) : NULL;
+                    _lst->next = lst->is_pair_obj() ? TO_PAIR(lst) : NULL;
                     lst = _lst;
                 }
             }