diff --git a/Makefile b/Makefile
index cc596b2..106ffab 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,13 @@
+.PHONY: run
 UNIVERSAL_SERVICE_DIR=universalservice
 CFLAGS=-I${UNIVERSAL_SERVICE_DIR}/include -g -I${UNIVERSAL_SERVICE_DIR}/examples/string -std=c89 -Wall -pedantic -Werror
 LDFLAGS=-L${UNIVERSAL_SERVICE_DIR} -luniversalservice -L${UNIVERSAL_SERVICE_DIR}/examples/string -lunsstring
 
 flatrate: main.c
 	$(CC) main.c -o flatrate $(CFLAGS) $(LDFLAGS)
+run: flatrate
+	LD_LIBRARY_PATH="$$(pwd)/${UNIVERSAL_SERVICE_DIR}/:$$(pwd)/${UNIVERSAL_SERVICE_DIR}/examples/string" ./flatrate < prelude.scm
+debug: flatrate
+	LD_LIBRARY_PATH="$$(pwd)/${UNIVERSAL_SERVICE_DIR}/:$$(pwd)/${UNIVERSAL_SERVICE_DIR}/examples/string" gdb -tui ./flatrate
+valgrind: flatrate
+	LD_LIBRARY_PATH="$$(pwd)/${UNIVERSAL_SERVICE_DIR}/:$$(pwd)/${UNIVERSAL_SERVICE_DIR}/examples/string" valgrind ./flatrate < prelude.scm
diff --git a/main.c b/main.c
index 7ec3acb..b9560b0 100644
--- a/main.c
+++ b/main.c
@@ -31,6 +31,7 @@
 #include "cheney_c89.h"
 
 static struct uns_gc gc;
+static struct uns_ctr empty_list;
 
 enum token_type {
 	T_EOF,
@@ -40,12 +41,13 @@ enum token_type {
 	QUASIQUOTE,
 	UNQUOTE,
 	UNQUOTE_LIST,
-	IDENT,
-	NUMBER,
-	STRING,
+	T_IDENT,
+	T_NUMBER,
+	T_STRING,
 	TOKEN_NUM
 };
 
+#if 0
 static const char *token2string[TOKEN_NUM] = {
 	"EOF",
 	"(",
@@ -55,9 +57,10 @@ static const char *token2string[TOKEN_NUM] = {
 	",",
 	",@",
 	"IDENT",
-	"NUMBER",
-	"STRING"
+	"NUMBER_TOK",
+	"STRING_TOK"
 };
+#endif
 
 struct token {
 	enum token_type typ;
@@ -92,7 +95,7 @@ static void tok_string(FILE *input, struct token *tok)
 {
 	int c;
 
-	tok->typ = STRING;
+	tok->typ = T_STRING;
 	uns_string_alloc(&gc, &tok->dat, 32);
 	for (;;) {
 		c = getc(input);
@@ -146,7 +149,7 @@ static void tok_num(FILE *input, struct token *tok, int mul)
 {
 	int c = getc(input);
 
-	tok->typ = NUMBER;
+	tok->typ = T_NUMBER;
 	uns_string_alloc(&gc, &tok->dat, 32);
 	do {
 		uns_string_append_char(&gc, &tok->dat, c);
@@ -167,7 +170,7 @@ static int part_of_ident(int c)
 
 static void tok_ident(FILE *input, struct token *tok, int c)
 {
-	tok->typ = IDENT;
+	tok->typ = T_IDENT;
 
 	uns_string_alloc(&gc, &tok->dat, 32);
 	do {
@@ -228,61 +231,302 @@ static void tokenize(FILE *input, struct token *tok)
 	}
 }
 
+enum item_type {
+	CELL,
+	LAMBDA,
+	INTEGER,
+	STRING,
+	SYMBOL,
+	EMPTY_LIST,
+	LISP_NULL
+};
+
+static void alloc_of_type(struct uns_ctr *ctr, int typ)
+{
+	void *p;
+	int fields;
+	int i;
+
+	switch (typ) {
+	case CELL: fields = 2; break;
+	case LAMBDA: fields = 2; break;
+	case INTEGER: fields = 1; break;
+	case STRING: fields = 1; break;
+	case SYMBOL: fields = 1; break;
+	case EMPTY_LIST: fields = 0; break;
+	case LISP_NULL: fields = 0; break;
+	}
+
+	ctr->p = gc.alloc_record(&gc, fields + 1);
+	p = gc.alloc(&gc, sizeof(int));
+	memcpy(p, &typ, sizeof(int));
+	gc.record_set_ptr(ctr->p, 0, p);
+
+	for (i = 0; i < fields; i++)
+		gc.record_set_ptr(ctr->p, i + 1, NULL);
+}
+
+static int get_type(Uns_ptr p)
+{
+	int typ;
+	void *innerp;
+
+	if (!p)
+		return LISP_NULL;
+	innerp = gc.record_get_ptr(p, 0);
+
+	memcpy(&typ, innerp, sizeof(int));
+	return typ;
+}
+
+static void alloc_symbol_from_cstring(struct uns_ctr *ctr, const char *s, size_t slen)
+{
+	struct uns_ctr str = {0};
+
+	uns_root_add(&gc, &str);
+	uns_string_alloc(&gc, &str, slen);
+	uns_string_append_bytes(&gc, &str, s, slen);
+
+	alloc_of_type(ctr, SYMBOL);
+	gc.record_set_ptr(ctr->p, 1, str.p);
+
+	uns_root_remove(&gc, &str);
+}
+
+static void alloc_integer(struct uns_ctr *ctr, long l)
+{
+	void *p;
+	alloc_of_type(ctr, INTEGER);
+
+	p = gc.alloc(&gc, sizeof(long));
+	memcpy(p, &l, sizeof(long));
+	gc.record_set_ptr(ctr->p, 1, p);
+}
+
+static int expr_all(FILE *input, struct token *tok, struct uns_ctr *expr);
+
+static int list_expr(FILE *input, struct uns_ctr *expr, struct token *tok)
+{
+	struct uns_ctr in_car = {0};
+	struct uns_ctr in_cdr = {0};
+	struct uns_ctr cur_head = {0};
+	int r = 1;
+
+	uns_root_add(&gc, &in_car);
+	uns_root_add(&gc, &in_cdr);
+	uns_root_add(&gc, &cur_head);
+
+	alloc_of_type(expr, CELL);
+	cur_head.p = expr->p;
+
+	for (;;) {
+		if (!expr_all(input, tok, &in_car)) {
+			r = 0;
+			goto end;
+		}
+
+		gc.record_set_ptr(cur_head.p, 1, in_car.p);
+
+		tokenize(input, tok);
+		if (tok->typ == RPAREN)
+			break;
+
+		alloc_of_type(&in_cdr, CELL);
+		gc.record_set_ptr(cur_head.p, 2, in_cdr.p);
+		cur_head.p = in_cdr.p;
+	}
+
+	gc.record_set_ptr(cur_head.p, 2, empty_list.p);
+end:
+	uns_root_remove(&gc, &in_car);
+	uns_root_remove(&gc, &in_cdr);
+	uns_root_remove(&gc, &cur_head);
+	return r;
+}
+
+static int surround_expr(FILE *input, struct uns_ctr *expr, struct token *tok, const char *name)
+{
+	struct uns_ctr tmp = {0};
+	struct uns_ctr quoted = {0};
+	int r = 0;
+
+	uns_root_add(&gc, &tmp);
+	uns_root_add(&gc, &quoted);
+
+	alloc_of_type(expr, CELL);
+
+	alloc_symbol_from_cstring(&tmp, name, strlen(name));
+	gc.record_set_ptr(expr->p, 1, tmp.p);
+
+	alloc_of_type(&tmp, CELL);
+	gc.record_set_ptr(expr->p, 2, tmp.p);
+
+	tokenize(input, tok);
+	if (expr_all(input, tok, &quoted)) {
+		r = 1;
+		gc.record_set_ptr(tmp.p, 1, quoted.p);
+		gc.record_set_ptr(tmp.p, 2, empty_list.p);
+	}
+
+	uns_root_remove(&gc, &tmp);
+	uns_root_remove(&gc, &quoted);
+	return r;
+}
+
+/* expr does not call tokenizer directly: it acts on an input token */
+static int expr_all(FILE *input, struct token *tok, struct uns_ctr *expr)
+{
+	switch (tok->typ) {
+	case LPAREN:
+		tokenize(input, tok);
+		if (tok->typ == RPAREN)
+			expr->p = empty_list.p;
+		else
+			return list_expr(input, expr, tok);
+		break;
+	case QUOTE:
+		return surround_expr(input, expr, tok, "quote");
+	case QUASIQUOTE:
+		return surround_expr(input, expr, tok, "quasiquote");
+	case UNQUOTE:
+		return surround_expr(input, expr, tok, "unquote");
+	case UNQUOTE_LIST:
+		return surround_expr(input, expr, tok, "unquote-list");
+	case T_IDENT:
+		alloc_of_type(expr, SYMBOL);
+		gc.record_set_ptr(expr->p, 1, tok->dat.p);
+		break;
+	case T_NUMBER:
+		alloc_integer(expr, tok->i);
+		break;
+	case T_STRING:
+		alloc_of_type(expr, STRING);
+		gc.record_set_ptr(expr->p, 1, tok->dat.p);
+		break;
+	case RPAREN: case T_EOF: case TOKEN_NUM:
+		return 0;
+	}
+
+	return 1;
+}
+
+static int read_next(FILE *input, struct uns_ctr *expr)
+{
+	struct token tok = {0};
+	int r = 0;
+
+	uns_root_add(&gc, &tok.dat);
+	tokenize(input, &tok);
+	expr->p = NULL;
+	if (tok.typ != T_EOF)
+		r = expr_all(input, &tok, expr);
+	uns_root_remove(&gc, &tok.dat);
+
+	return r;
+}
+
 static void oom(struct uns_gc *gc_)
 {
 	(void)gc_;
 	printf("oom\n");
-	exit(1);
+	abort();
 }
 
 static void after_gc(struct uns_gc *gc_)
 {
 	(void)gc_;
 
-	if (gc.after_collection >= gc.next_alloc * 7/10)
-		gc.next_alloc *= 2;
+	fprintf(stderr,
+	        "The garbage collector has run %ld times\n"
+	        "\tbefore collection: %lu\n"
+	        "\tafter collection: %lu\n",
+	        gc.collection_number,
+	        gc.before_collection,
+	        gc.after_collection
+	);
+
+
+	gc.next_alloc *= 2;
 }
 
-int main(void)
+static void init_gc(void)
 {
-	FILE *input = stdin;
-	struct token tok;
-	int indent = 0;
-	int i;
-
 	gc.next_alloc = 512;
 	gc.oom = oom;
 	gc.after_gc = after_gc;
 
 	gc.ctx = malloc(uns_cheney_c89_ctx_size);
 	if(!gc.ctx || !uns_cheney_c89_init(&gc))
-		return 1;
-	uns_root_add(&gc, &tok.dat);
+		exit(1);
+	gc.next_alloc *= 2;
 
-	do {
-		tokenize(input, &tok);
-		if (tok.typ == LPAREN)
-			indent++;
-		else if (tok.typ == RPAREN)
-			indent--;
+	uns_root_add(&gc, &empty_list);
+	alloc_of_type(&empty_list, EMPTY_LIST);
+}
 
-		for (i = 0; i < indent; i++)
-			printf(" ");
+static void display(struct uns_ctr *ctr)
+{
+	struct uns_ctr tmp = {0};
+	long l;
 
-		printf("%s ", token2string[tok.typ]);
-		switch (tok.typ) {
-		case STRING: case IDENT:
-			printf("[%s] ", uns_string_cstring(&gc, &tok.dat));
-			break;
-		case NUMBER:
-			printf("[%ld] ", tok.i);
-			break;
-		default:
-			break;
-		}
+	if (!ctr->p) {
+		printf("__null");
+		return;
+	}
+
+	switch (get_type(ctr->p)) {
+	case CELL:
+		uns_root_add(&gc, &tmp);
+
+		printf("(");
+		tmp.p = gc.record_get_ptr(ctr->p, 1);
+		display(&tmp);
+
+		printf(" . ");
+
+		tmp.p = gc.record_get_ptr(ctr->p, 2);
+		display(&tmp);
+		printf(")");
+
+		uns_root_remove(&gc, &tmp);
+		return;
+	case INTEGER:
+		memcpy(&l, gc.record_get_ptr(ctr->p, 1), sizeof(long));
+		printf("%ld ", l);
+		return;
+	case STRING:
+		tmp.p = gc.record_get_ptr(ctr->p, 1);
+		uns_root_add(&gc, &tmp);
+		printf("\"%s\" ", uns_string_cstring(&gc, &tmp));
+		uns_root_remove(&gc, &tmp);
+		return;
+	case SYMBOL:
+		tmp.p = gc.record_get_ptr(ctr->p, 1);
+		uns_root_add(&gc, &tmp);
+		printf("'%s ", uns_string_cstring(&gc, &tmp));
+		uns_root_remove(&gc, &tmp);
+		return;
+	case EMPTY_LIST:
+		printf("'() ");
+		return;
+	default:
+		abort();
+	}
+}
+
+int main(void)
+{
+	struct uns_ctr expr = {0};
+
+	init_gc();
+	uns_root_add(&gc, &expr);
+
+	while (read_next(stdin, &expr)) {
+		display(&expr);
 		printf("\n");
-	} while (tok.typ != T_EOF);
+	}
 
+	uns_root_remove(&gc, &expr);
 	uns_cheney_c89_deinit(&gc);
 	return 0;
 }