diff --git a/Makefile b/Makefile
index f938054..45e9534 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC=gcc
-CFLAGS=-std=gnu99 -g -Wall
+CFLAGS=-std=gnu99 -O2 -Wall -Wshadow -Wextra -Wno-unused-parameter
 LDFLAGS=
 
 .PHONY: clean test
diff --git a/README.md b/README.md
index 5c8a721..6d5990d 100644
--- a/README.md
+++ b/README.md
@@ -85,19 +85,15 @@ CTRL-Z         SUSPEND PROCESS
 The REPL also saves the history of commands in the file history.txt
 This file is loaded at startup, so one can recall previous commands.
 
-Future improvements:
-- floating point numbers
-- data files
-- system calls
-
 Known bugs:
-* the paste function does not work very well.
+* Operators "and" and "or" do not work like their typical Lisp counterpart 
+because they evaluate all their operands at the same time instead of one
+by one. You may use the versions in the library.lisp file to correct this behavior.
 * recall of multiline commands does not work as expected.
-* this doesn't have tail call optimization, so expect crashes with sometimes surprisingly short lists. 
-
+* this doesn't have tail call optimization, so expect crashes with sometimes with surprisingly short lists. 
 
 Original README (completed)
----------------
+===============
 
 One day I wanted to see what I can do with 1k lines of C and
 decided to write a Lisp interpreter. That turned to be a
@@ -269,7 +265,8 @@ exhaustion error.
 
     ( progn (print "I own ")
             (defun add(x y)(+ x y))
-            (println (add 3 7) " cents") )  ; -> prints "I own 10 cents"
+            (print (add 3 7) 
+            (println " cents") )  ; -> prints "I own 10 cents"
 
 ### Equivalence test operators
 
@@ -414,15 +411,3 @@ than itself. Useful for writing a macro that introduces new identifiers.
 
 As in the traditional Lisp syntax, `;` (semicolon) starts a single line comment.
 The comment continues to the end of line.
-
-No GC Branch
-------------
-
-There is a MiniLisp branch from which the code for garbage collection has been
-stripped. The accepted language is the same, but the code is simpler than the
-master branch's one. The reader might want to read the nogc branch first, then
-proceed to the master branch, to understand the code step by step.
-
-The nogc branch is available at
-[nogc](https://github.com/rui314/minilisp/tree/nogc). The original is available
-at [master](https://github.com/rui314/minilisp).
diff --git a/src/gc.c b/src/gc.c
index bbc299c..3f4dab0 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -116,11 +116,6 @@ void *alloc_semispace() {
     return mmap(NULL, MEMORY_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
 }
 
-void free_semispace(void *ptr){
-    if (ptr) munmap(ptr, MEMORY_SIZE);
-    mem_nused = 0;
-}
-
 // Copies the root objects.
 static void forward_root_objects(void *root) {
     Symbols = forward(Symbols);
@@ -141,7 +136,7 @@ static bool getEnvFlag(char *name) {
 // http://en.wikipedia.org/wiki/Cheney%27s_algorithm
 void gc(void *root) {
     assert(!gc_running);
-    gc_running = true; // 開始垃圾蒐集
+    gc_running = true;
 
     // Debug flags
     debug_gc = getEnvFlag("MINILISP_DEBUG_GC");
diff --git a/src/minilisp.c b/src/minilisp.c
index 40094a4..43de35a 100644
--- a/src/minilisp.c
+++ b/src/minilisp.c
@@ -28,10 +28,10 @@ void error(char *fmt, int line_num, ...) {
 }
 
 // Constants
-static Obj *True = &(Obj){ TTRUE };
-static Obj *Nil = &(Obj){ TNIL };
-static Obj *Dot = &(Obj){ TDOT };
-static Obj *Cparen = &(Obj){ TCPAREN };
+static Obj *True = &(Obj){ .type = TTRUE, .size = sizeof(Obj) };
+static Obj *Nil = &(Obj){ .type = TNIL, .size = sizeof(Obj) };
+static Obj *Dot = &(Obj){ .type = TDOT, .size = sizeof(Obj) };
+static Obj *Cparen = &(Obj){ .type = TCPAREN, .size = sizeof(Obj) };
 
 //======================================================================
 // Constructors
@@ -263,15 +263,8 @@ static Obj *read_string(void *root) {
 static Obj *read_expr(void *root) {
     for (;;) {
         char c = read_char();
-        if (c == '\n') {
-            if (peek() == '\r');
+        if (c == ' ' || c == '\n' || c == '\r' || c == '\t')
             continue;
-        }
-
-        if (c == ' ' || c == '\r' || c == '\t')
-            continue;
-        if (c == EOF)
-            return NULL;
         if (c == ';') {
             skip_line();
             continue;
@@ -292,6 +285,9 @@ static Obj *read_expr(void *root) {
             return make_int(root, -read_number(0));
         if (isalpha(c) || strchr(symbol_chars, c))
             return read_symbol(root, c);
+        if (c == EOF)
+            return NULL;
+
         error("Don't know how to handle %c", filepos.line_num, c);
     }
 }
@@ -808,9 +804,9 @@ static Obj *prim_macroexpand(void *root, Obj **env, Obj **list) {
 
 // (print ...)
 static Obj *prim_print(void *root, Obj **env, Obj **list) {
-    for (Obj *args = *list; args != Nil; args = args->cdr) {
-        print(eval(root, env, &(args->car)));
-    }
+    DEFINE1(root, tmp);
+    *tmp = (*list)->car;
+    print(eval(root, env, tmp));
     return Nil;
 }
 
@@ -1023,6 +1019,8 @@ static void define_primitives(void *root, Obj **env) {
     add_primitive(root, env, "while", prim_while);
     add_primitive(root, env, "gensym", prim_gensym);
     add_primitive(root, env, "not", prim_not);
+    add_primitive(root, env, "and", prim_and);
+    add_primitive(root, env, "or", prim_or);
     add_primitive(root, env, "+", prim_plus);
     add_primitive(root, env, "-", prim_minus);
     add_primitive(root, env, "*", prim_mult);
@@ -1060,20 +1058,16 @@ static void define_primitives(void *root, Obj **env) {
 
 extern void *memory;
 
-void reset_minilisp(Obj **env) {
+void init_minilisp(Obj **env) {
     // Memory allocation
-    extern void *memory;
     extern void *alloc_semispace();
-    extern void free_semispace(void *);
-    gc_root = NULL;
-    free_semispace(memory);
     memory = alloc_semispace();
 
     // Constants and primitives
     Symbols = Nil;
-    *env = make_env(gc_root, &Nil, &Nil);
-    define_constants(gc_root, env);
-    define_primitives(gc_root, env);
+    *env = make_env(NULL, &Nil, &Nil);
+    define_constants(NULL, env);
+    define_primitives(NULL, env);
 }
 
 int eval_input(void *root, Obj **env, Obj **expr) {
diff --git a/src/repl.c b/src/repl.c
index c7aae7c..785bd49 100644
--- a/src/repl.c
+++ b/src/repl.c
@@ -75,6 +75,7 @@ void minilisp(char *text, size_t length, bool with_repl, Obj **env, Obj **expr)
     if (with_repl)
         for(int promptnum = 1;; promptnum++) {
             char prompt[15] = "";
+            filepos = (filepos_t){ .filename = "", .file_len = 0, .line_num = 1 };
             sprintf(prompt, "%d:", promptnum);
             char *line = bestline(prompt);
             if(line == NULL) continue;
@@ -96,14 +97,9 @@ void minilisp(char *text, size_t length, bool with_repl, Obj **env, Obj **expr)
                     extern size_t mem_nused;
                     printf("Memory used: %ld / Total: %d\n", mem_nused, MEMORY_SIZE);
                 }
-                else if (!strncmp(line, "/reset", 6)){
-                    DEFINE1(gc_root, env);
-                    reset_minilisp(env);
-                }
                 else if (!strncmp(line, "/help", 5)){
                     puts("Type Ctrl-C to quit.");
                     puts("/memory to display the amount of memory used.");
-                    puts("/reset to flush the interpreter objects.");
                 }
                 else {
                     printf("Unreconized command: %s", line);
@@ -220,7 +216,7 @@ int main(int argc, char **argv) {
     parse_args(argc, argv);
 
     DEFINE2(gc_root, env, expr);
-    reset_minilisp(env);
+    init_minilisp(env);
 
     for (int i = 0; i < num_files; i++) {
         printf("Loading %s\n", filenames[i]);
diff --git a/test.sh b/test.sh
index 5e47517..bf902e5 100755
--- a/test.sh
+++ b/test.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/bash -x
 
 function fail() {
   echo -n -e '\e[1;31m[ERROR]\e[0m '
@@ -7,13 +7,13 @@ function fail() {
 }
 
 function do_run() {
-  error=$(echo "$3" | ./minilisp 2>&1 > /dev/null)
+  error=$(echo "$3" | ./minilisp -r -x "${3}" 2>&1 > /dev/null)
   if [ -n "$error" ]; then
     echo FAILED
     fail "$error"
   fi
 
-  result=$(echo "$3" | ./minilisp 2> /dev/null | tail -1)
+  result=$(echo "$3" | ./minilisp -r -x "${3}" 2> /dev/null | tail -1)
   if [ "$result" != "$2" ]; then
     echo FAILED
     fail "$2 expected, but got $result"
@@ -136,9 +136,9 @@ run restargs '(3)'    '(defun f (x . y) (cons x y)) (f 3)'
 
 # strings
 run 'string-concat' 'one & two and 3' '(string-concat "one" " & " "two" " and " 3)'
-#run 'symbol->string' 'twelve' "
-#  (define twelve 12)
-#  (symbol->string 'twelve)"
+run 'symbol->string' 'twelve' "
+  (define twelve 12)
+  (symbol->string 'twelve)"
 run 'string->symbol' 'twelve' '(string->symbol "twelve")'
 
 # Lexical closures
@@ -154,9 +154,10 @@ run counter 3 '
   (counter)
   (counter)'
 
-#run progn 'I own 10 cents' '(progn (print "I own ") 
-#                              (defun add(x y)(+ x y))
-#                              (println (add 3 7) " cents"))'
+run progn 'I own 10 cents()' '(progn (print "I own ") 
+                              (defun add(x y)(+ x y))
+                              (print (add 3 7)) 
+                              (print " cents"))'
 
 # While loop
 run while 45 "