From 6a496753148a9f6d9cc1c5e1651becceb4f3a275 Mon Sep 17 00:00:00 2001
From: Kyle Isom <kyle@imap.cc>
Date: Tue, 27 Feb 2018 19:59:29 -0800
Subject: [PATCH] misc/kforth: Add system status, work on vocab, better
 write_num.

- Now system structure includes a status variable and an associated
  function for writing the status out.
- Adding more words to the builtin dictionary.
- write_num round 3.
- Include option to not print the stack each iteration.
---
 Makefile          |   7 +-
 defs.h            |   1 +
 dict.cc           | 948 +++++++++++++++++++++++++++++++++++++++++++++-
 dict.h            |   9 +-
 doc/part-0x05.rst |   2 +-
 io.cc             |  42 +-
 io.h              |   4 +
 kforth.cc         |  59 +--
 linux/defs.h      |   2 +
 linux/io.h        |   2 +
 parser.cc         |   4 +-
 stack.h           |  18 +
 system.cc         |  64 ++++
 system.h          |  15 +-
 14 files changed, 1080 insertions(+), 97 deletions(-)
 create mode 100644 system.cc

diff --git a/Makefile b/Makefile
index 4a09afc..b8d3250 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,9 @@
 CXXSTD :=	c++14
-CXXFLAGS :=	-std=$(CXXSTD) -Wall -Werror -g -O0
+CXXFLAGS :=	-std=$(CXXSTD) -Wall -Werror -Os -static
+LDFLAGS :=	-static
 OBJS :=		linux/io.o	\
 		io.o		\
+		system.o	\
 		parser.o	\
 		word.o		\
 		dict.o		\
@@ -11,7 +13,8 @@ TARGET :=	kforth
 all: $(TARGET)
 
 $(TARGET): $(OBJS)
-	$(CXX) $(CFLAGS) -o $@ $(OBJS)
+	$(CXX) $(CXXFLAGS) -o $@ $(OBJS)
+	strip $@
 
 clean:
 	rm -f $(OBJS) $(TARGET)
diff --git a/defs.h b/defs.h
index e070d27..8dff6ad 100644
--- a/defs.h
+++ b/defs.h
@@ -5,6 +5,7 @@
 #include "linux/defs.h"
 #else
 typedef int KF_INT;
+typedef long KF_LONG;
 constexpr uint8_t STACK_SIZE = 16;
 #endif
 
diff --git a/dict.cc b/dict.cc
index 96f18b7..a6a173f 100644
--- a/dict.cc
+++ b/dict.cc
@@ -4,23 +4,87 @@
 #include "system.h"
 #include "word.h"
 
+#include <stdlib.h>
 #include <string.h>
 
+constexpr size_t dshift = (sizeof(KF_INT) * 8) - 1;
+
+static bool
+pop_long(System *sys, KF_LONG *d)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	*d = a << dshift;
+	*d += b;
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static inline KF_INT
+mask(size_t bits)
+{
+	KF_INT m = 0;
+
+	for (size_t i = 0; i < bits; i++) {
+		m += 1 << i;
+	}
+	
+	return m;
+}
+
+static bool
+push_long(System *sys, KF_LONG d)
+{
+	KF_INT	a = static_cast<KF_INT>((d >> dshift) & mask(dshift));
+	KF_INT	b = static_cast<KF_INT>(d & mask(dshift));
+
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
 static bool
 add(System *sys)
 {
 	KF_INT	a = 0;
 	KF_INT	b = 0;
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	a += b;
-	return sys->dstack.push(a);
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 static bool
@@ -29,15 +93,23 @@ sub(System *sys)
 	KF_INT	a = 0;
 	KF_INT	b = 0;
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	b -= a;
-	return sys->dstack.push(b);
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 static bool
@@ -45,16 +117,25 @@ mul(System *sys)
 {
 	KF_INT	a = 0;
 	KF_INT	b = 0;
+
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	b *= a;
-	return sys->dstack.push(b);
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 static bool
@@ -63,15 +144,23 @@ div(System *sys)
 	KF_INT	a = 0;
 	KF_INT	b = 0;
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	b /= a;
-	return sys->dstack.push(b);
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 static bool
@@ -80,18 +169,27 @@ swap(System *sys)
 	KF_INT	a = 0;
 	KF_INT	b = 0;
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
 		return false;
 	}
 	
-	return sys->dstack.push(b);
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 static bool
@@ -100,27 +198,39 @@ rot(System *sys)
 	KF_INT	a = 0;
 	KF_INT	b = 0;
 	KF_INT	c = 0;
+
 	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.pop(&c)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
 		return false;
 	}
 	
 	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
 		return false;
 	}
 	
-	return sys->dstack.push(c);
+	if (!sys->dstack.push(c)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
 }
 
 // TODO: print multiple per line
@@ -161,6 +271,755 @@ definitions(System *sys)
 	}
 
 	sys->interface->wrln(line, linelen);
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+bye(System *sys)
+{
+	exit(0);
+	return true;
+}
+
+static bool
+dup(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+drop(System *sys)
+{
+	KF_INT	a;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+dotess(System *sys)
+{
+	write_dstack(sys->interface, sys->dstack);
+	sys->interface->newline();
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+dot(System *sys)
+{
+	KF_INT	a;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	write_num(sys->interface, a);
+	sys->interface->newline();
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+depth(System *sys)
+{
+	KF_INT	a = static_cast<KF_INT>(sys->dstack.size());
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+times_divide(System *sys)
+{
+	KF_INT	a, b, c;
+	KF_LONG	z;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&c)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	z = static_cast<KF_LONG>(c) * static_cast<KF_LONG>(b);
+	z /= static_cast<KF_LONG>(a);
+	a = static_cast<KF_INT>(z);
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+times_divide_mod(System *sys)
+{
+	KF_INT	a, b, c;
+	KF_LONG	y, z;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&c)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	z = static_cast<KF_LONG>(c) * static_cast<KF_LONG>(b);
+	y = z % static_cast<KF_LONG>(a);
+	z /= static_cast<KF_LONG>(a);
+	a = static_cast<KF_INT>(z);
+	b = static_cast<KF_INT>(y);
+
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+divide_mod(System *sys)
+{
+	KF_INT	a, b;
+	KF_INT	y, z;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	
+	z = b / a;
+	y = b % a;
+
+	if (!sys->dstack.push(y)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(z)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+
+/*
+static bool
+store(System *sys)
+{
+	KF_INT	a = 0; // address
+	KF_INT	b = 0; // value
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	KF_INT	*p = (KF_INT *)(a);
+	*p = b;
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+plus_store(System *sys)
+{
+	KF_INT	a = 0; // address
+	KF_INT	b = 0; // value
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	KF_INT	*p = (KF_INT *)(a);
+	*p += b;
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+*/
+
+static bool
+zero_less(System *sys)
+{
+	KF_INT	a;
+	bool	ok;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (a < 0) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+zero_equals(System *sys)
+{
+	KF_INT	a;
+	bool	ok;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (a == 0) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+zero_greater(System *sys)
+{
+	KF_INT	a;
+	bool	ok;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (a > 0) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+one_plus(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a++;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+one_minus(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a--;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+two_plus(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a += 2;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+two_minus(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a -= 2;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+two_divide(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a >>= 1;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+less_than(System *sys)
+{
+	KF_INT	a, b;
+	bool	ok;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (b < a) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+equals(System *sys)
+{
+	KF_INT	a, b;
+	bool	ok;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (b == a) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+greater_than(System *sys)
+{
+	KF_INT	a, b;
+	bool	ok;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (b > a) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+question_dupe(System *sys)
+{
+	KF_INT	a;
+
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	if (a != 0) {
+		if (!sys->dstack.push(a)) {
+			sys->status = STATUS_STACK_OVERFLOW;
+			return false;
+		}
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+absolute(System *sys)
+{
+	KF_INT	a;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (a < 0) {
+		if (!sys->dstack.push(-a)) {
+			sys->status = STATUS_STACK_OVERFLOW;
+			return false;
+		}
+	}
+	else {
+		if (!sys->dstack.push(a)) {
+			sys->status = STATUS_STACK_OVERFLOW;
+			return false;
+		}
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+land(System *sys)
+{
+	KF_INT	a, b;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a &= b;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+lor(System *sys)
+{
+	KF_INT	a, b;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.pop(&b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a |= b;
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+roll(System *sys)
+{
+	KF_INT	a, b;
+	size_t	i;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	i = sys->dstack.size() - static_cast<size_t>(a) - 1;
+	if (!sys->dstack.remove(i, &b)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	if (!sys->dstack.push(b)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+over(System *sys)
+{
+	KF_INT	a;
+	size_t	i = sys->dstack.size() - 2;
+	
+	if (!sys->dstack.get(i, a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+dplus(System *sys)
+{
+	KF_LONG	da, db;
+	
+	if (!pop_long(sys, &da)) {
+		// Status is already set.
+		return false;
+	}
+	
+	if (!pop_long(sys, &db)) {
+		// Status is already set.
+		return false;
+	}
+	
+	da += db;
+	
+	if (!push_long(sys, da)) {
+		// Status is already set.
+		return false;
+	}
+	
+	// Status is already set.
+	return true;
+}
+
+static bool
+dlt(System *sys)
+{
+	KF_LONG	da, db;
+	bool	ok;
+	
+	if (!pop_long(sys, &da)) {
+		// Status is already set.
+		return false;
+	}
+	
+	if (!pop_long(sys, &db)) {
+		// Status is already set.
+		return false;
+	}
+	
+	if (db < da) {
+		ok = sys->dstack.push(-1);
+	}
+	else {
+		ok = sys->dstack.push(0);
+	}
+	
+	if (!ok) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
+	return true;
+}
+
+static bool
+negate(System *sys)
+{
+	KF_INT	a;
+	
+	if (!sys->dstack.pop(&a)) {
+		sys->status = STATUS_STACK_UNDERFLOW;
+		return false;
+	}
+	
+	a = ~a;
+	a++;
+	
+	if (!sys->dstack.push(a)) {
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
+	}
+	
+	sys->status = STATUS_OK;
 	return true;
 }
 
@@ -168,17 +1027,47 @@ void
 init_dict(System *sys)
 {
 	sys->dict = nullptr;
-	sys->dict = new Builtin((const char *)"DEFINITIONS", 11, sys->dict, definitions);
-	sys->dict = new Builtin((const char *)"+", 1, sys->dict, add);
-	sys->dict = new Builtin((const char *)"-", 1, sys->dict, sub);
-	sys->dict = new Builtin((const char *)"*", 1, sys->dict, mul);
-	sys->dict = new Builtin((const char *)"/", 1, sys->dict, div);
 	sys->dict = new Builtin((const char *)"SWAP", 4, sys->dict, swap);
 	sys->dict = new Builtin((const char *)"ROT", 3, sys->dict, rot);
+	sys->dict = new Builtin((const char *)"ROLL", 4, sys->dict, roll);
+	sys->dict = new Builtin((const char *)"OVER", 4, sys->dict, over);
+	sys->dict = new Builtin((const char *)"NEGATE", 6, sys->dict, negate);
+	sys->dict = new Builtin((const char *)"OR", 2, sys->dict, lor);
+	sys->dict = new Builtin((const char *)"DUP", 3, sys->dict, dup);
+	sys->dict = new Builtin((const char *)"DROP", 4, sys->dict, drop);
+	sys->dict = new Builtin((const char *)"DEPTH", 5, sys->dict, depth);
+	sys->dict = new Builtin((const char *)"DEFINITIONS", 11, sys->dict, definitions);
+	sys->dict = new Builtin((const char *)"D<", 2, sys->dict, dlt);
+	sys->dict = new Builtin((const char *)"D+", 2, sys->dict, dplus);
+	sys->dict = new Builtin((const char *)"BYE", 3, sys->dict, bye);
+	sys->dict = new Builtin((const char *)"ABS", 3, sys->dict, absolute);
+	sys->dict = new Builtin((const char *)"AND", 3, sys->dict, land);
+	sys->dict = new Builtin((const char *)"?DUP", 4, sys->dict, question_dupe);
+	sys->dict = new Builtin((const char *)">", 1, sys->dict, greater_than);
+	sys->dict = new Builtin((const char *)"=", 1, sys->dict, equals);
+	sys->dict = new Builtin((const char *)"<", 1, sys->dict, less_than);
+	sys->dict = new Builtin((const char *)"2/", 2, sys->dict, two_divide);
+	sys->dict = new Builtin((const char *)"2-", 2, sys->dict, two_minus);
+	sys->dict = new Builtin((const char *)"2+", 2, sys->dict, two_plus);
+	sys->dict = new Builtin((const char *)"1-", 2, sys->dict, one_minus);
+	sys->dict = new Builtin((const char *)"1+", 2, sys->dict, one_plus);
+	sys->dict = new Builtin((const char *)"0>", 2, sys->dict, zero_greater);
+	sys->dict = new Builtin((const char *)"0=", 2, sys->dict, zero_equals);
+	sys->dict = new Builtin((const char *)"0<", 2, sys->dict, zero_less);
+	sys->dict = new Builtin((const char *)"*/MOD", 5, sys->dict, times_divide_mod);
+	sys->dict = new Builtin((const char *)"*/", 2, sys->dict, times_divide);
+	sys->dict = new Builtin((const char *)"/MOD", 4, sys->dict, divide_mod);
+	sys->dict = new Builtin((const char *)"/", 1, sys->dict, div);
+	sys->dict = new Builtin((const char *)".S", 2, sys->dict, dotess);
+	sys->dict = new Builtin((const char *)".", 1, sys->dict, dot);
+	sys->dict = new Builtin((const char *)"-", 1, sys->dict, sub);
+	// sys->dict = new Builtin((const char *)"+!", 2, sys->dict, plus_store);
+	sys->dict = new Builtin((const char *)"+", 1, sys->dict, add);
+	sys->dict = new Builtin((const char *)"*", 1, sys->dict, mul);
+	// sys->dict = new Builtin((const char *)"!", 1, sys->dict, store);
 }
 
-
-LOOKUP
+bool
 lookup(struct Token *token, System *sys)
 {
 	Word	*cursor = sys->dict;
@@ -186,20 +1075,39 @@ lookup(struct Token *token, System *sys)
 	
 	if (parse_num(token, &n)) {
 		if (sys->dstack.push(n)) {
-			return LOOKUP_OK;
+			sys->status = STATUS_OK;
+			return true;
 		}
-		return LOOKUP_FAILED;
+		sys->status = STATUS_STACK_OVERFLOW;
+		return false;
 	}
 	
 	while (cursor != nullptr) {
 		if (cursor->match(token)) {
-			if (cursor->eval(sys)) {
-				return LOOKUP_OK;
+			if (!cursor->eval(sys)) {
+				sys->dstack.clear();
+				return false;
 			}
-			return LOOKUP_FAILED;
+			return true;
 		}
 		cursor = cursor->next();
 	}
 	
-	return LOOKUP_NOTFOUND;
-}
\ No newline at end of file
+	sys->status = STATUS_UNKNOWN_WORD;
+	return false;
+}
+
+void
+reset_system(System *sys)
+{
+	sys->status = STATUS_OK;
+	sys->dstack.clear();
+	
+	auto cursor = sys->dict;
+	auto next   = cursor;
+	while (cursor != nullptr) {
+		next = cursor->next();
+		delete cursor;
+		cursor = next;
+	}
+}
diff --git a/dict.h b/dict.h
index e9b5677..9085492 100644
--- a/dict.h
+++ b/dict.h
@@ -6,14 +6,9 @@
 #include "system.h"
 #include "word.h"
 
-typedef enum _LOOKUP_ : uint8_t {
-	LOOKUP_OK = 0,	     // Lookup executed properly.
-	LOOKUP_NOTFOUND = 1, // The token isn't in the dictionary.
-	LOOKUP_FAILED = 2    // The word failed to execute.
-} LOOKUP;
-
 void	init_dict(System *);
-LOOKUP	lookup(struct Token *, System *);
+void	reset_system(System *);
+bool	lookup(struct Token *, System *);
 
 
 
diff --git a/doc/part-0x05.rst b/doc/part-0x05.rst
index 8cc5d5b..b3decf2 100644
--- a/doc/part-0x05.rst
+++ b/doc/part-0x05.rst
@@ -1,7 +1,7 @@
 Write You a Forth, 0x05
 -----------------------
 
-:date: 2018-02-24 12:23
+:date: 2018-02-27 08:06
 :tags: wyaf, forth
 
 NB: Today's update was pretty large, so I don't show all of the code; this is
diff --git a/io.cc b/io.cc
index a86156b..bdb27cc 100644
--- a/io.cc
+++ b/io.cc
@@ -8,21 +8,12 @@ static constexpr size_t	nbuflen = 11;
 void
 write_num(IO *interface, KF_INT n)
 {
-
-	// TODO(kyle): make the size of the buffer depend on the size of
-	// KF_INT.
 	char buf[nbuflen];
-	uint8_t i = nbuflen;
-	memset(buf, 0, i);
-	bool neg = n < 0;
+	uint8_t i = nbuflen - 1;
+	memset(buf, 0, nbuflen);
 
 	if (n < 0) {
 		interface->wrch('-');
-		n = ~n;
-		if (n == 0) {
-			neg = false;
-			n++;
-		}
 	}
 	else if (n == 0) {
 		interface->wrch('0');
@@ -30,13 +21,28 @@ write_num(IO *interface, KF_INT n)
 	}
 
 	while (n != 0) {
-		char ch = (n % 10) + '0';
-		if (neg && (i == nbuflen)) ch++;
-		buf[i-1] = ch;
-		i--;
+		char x = n % 10;
+		x = x < 0 ? -x : x;
+		x += '0';
+		buf[i--] = x;
 		n /= 10;
 	}
 
-	uint8_t buflen = nbuflen - i % nbuflen;
-	interface->wrbuf(buf+i, buflen);
-}
\ No newline at end of file
+	interface->wrbuf(buf+i, nbuflen - i);
+}
+
+void
+write_dstack(IO *interface, Stack<KF_INT> dstack)
+{
+	KF_INT	tmp;
+	interface->wrch('<');
+	for (size_t i = 0; i < dstack.size(); i++) {
+		if (i > 0) {
+			interface->wrch(' ');
+		}
+
+		dstack.get(i, tmp);
+		write_num(interface, tmp);
+	}
+	interface->wrch('>');
+}
diff --git a/io.h b/io.h
index 38bf51b..8604546 100644
--- a/io.h
+++ b/io.h
@@ -2,6 +2,7 @@
 #define __KF_IO_H__
 
 #include "defs.h"
+#include "stack.h"
 
 class IO {
 public:
@@ -19,9 +20,12 @@ public:
 	// Line I/O
 	virtual bool	rdln(char *buf, size_t len, size_t *readlen) = 0;
 	virtual void	wrln(char *buf, size_t len) = 0;
+	
+	virtual void	newline(void) = 0;
 };
 
 void	write_num(IO *, KF_INT);
+void	write_dstack(IO *, Stack<KF_INT>);
 
 
 #endif // __KF_IO_H__
\ No newline at end of file
diff --git a/kforth.cc b/kforth.cc
index 565b5b0..73cc528 100644
--- a/kforth.cc
+++ b/kforth.cc
@@ -10,25 +10,10 @@
 #include "linux.h"
 #endif // __linux__
 
-static char     ok[] = "ok.\n";
 static System	sys;
-
-
-static void
-write_dstack()
-{
-	KF_INT	tmp;
-	sys.interface->wrch('<');
-	for (size_t i = 0; i < sys.dstack.size(); i++) {
-		if (i > 0) {
-			sys.interface->wrch(' ');
-		}
-
-		sys.dstack.get(i, tmp);
-		write_num(sys.interface, tmp);
-	}
-	sys.interface->wrch('>');
-}
+#ifndef TRACE_STACK
+#define TRACE_STACK false
+#endif
 
 static bool
 parser(const char *buf, const size_t buflen)
@@ -36,8 +21,6 @@ parser(const char *buf, const size_t buflen)
 	static size_t		offset = 0;
 	static struct Token	token;
 	static PARSE_RESULT	result = PARSE_FAIL;
-	static LOOKUP		lresult = LOOKUP_FAILED;
-	static bool		stop = false;
 
 	offset = 0;
 
@@ -46,34 +29,17 @@ parser(const char *buf, const size_t buflen)
 	token.length = 0;
 
 	while ((result = parse_next(buf, buflen, &offset, &token)) == PARSE_OK) {
-		lresult = lookup(&token, &sys);
-		switch (lresult) {
-		case LOOKUP_OK:
-			continue;
-		case LOOKUP_NOTFOUND:
-			sys.interface->wrln((char *)"word not found", 15);
-			stop = true;
-			break;
-		case LOOKUP_FAILED:
-			sys.interface->wrln((char *)"execution failed", 17);
-			stop = true;
-			break;
-		default:
-			sys.interface->wrln((char *)"*** the world is broken ***", 27);
-			exit(1);
-		}
-		
-		if (stop) {
-			stop = false;
+		if (!lookup(&token, &sys)) {
 			break;
 		}
 	}
 
+	system_write_status(&sys);
+	sys.interface->newline();
 	switch (result) {
 	case PARSE_OK:
 		return false;
 	case PARSE_EOB:
-		sys.interface->wrbuf(ok, 4);
 		return true;
 	case PARSE_LEN:
 		sys.interface->wrln((char *)"parse error: token too long", 27);
@@ -94,8 +60,10 @@ interpreter()
 	static char linebuf[81];
 
 	while (true) {
-		write_dstack();
-		sys.interface->wrch('\n');
+		if (TRACE_STACK) {
+			write_dstack(sys.interface, sys.dstack);
+			sys.interface->newline();
+		}
 		sys.interface->wrch('?');
 		sys.interface->wrch(' ');
 		buflen = sys.interface->rdbuf(linebuf, 80, true, '\n');
@@ -103,18 +71,19 @@ interpreter()
 	}
 }
 
-static char	banner[] = "kforth interpreter\n";
-const size_t	bannerlen = 19;
+static char	banner[] = "kforth interpreter";
+const size_t	bannerlen = 18;
 
 int
 main(void)
 {
+	reset_system(&sys);
 	init_dict(&sys);
 #ifdef __linux__
 	Console interface;
 	sys.interface = &interface;
 #endif
-	sys.interface->wrbuf(banner, bannerlen);
+	sys.interface->wrln(banner, bannerlen);
 	interpreter();
 	return 0;
 }
\ No newline at end of file
diff --git a/linux/defs.h b/linux/defs.h
index 3740f5a..edcbdb2 100644
--- a/linux/defs.h
+++ b/linux/defs.h
@@ -5,6 +5,8 @@
 #include <stdint.h>
 
 typedef int32_t KF_INT;
+typedef int64_t	KF_LONG;
+
 constexpr uint8_t	STACK_SIZE = 128;
 
 #endif
\ No newline at end of file
diff --git a/linux/io.h b/linux/io.h
index a64e7e4..7de9acb 100644
--- a/linux/io.h
+++ b/linux/io.h
@@ -17,6 +17,8 @@ public:
 	// Line I/O
 	bool	rdln(char *buf, size_t len, size_t *readlen);
 	void	wrln(char *buf, size_t len);
+	
+	void	newline(void) { this->wrch('\n'); };
 private:
 };
 
diff --git a/parser.cc b/parser.cc
index 5d26ba4..c52bd4d 100644
--- a/parser.cc
+++ b/parser.cc
@@ -5,7 +5,7 @@
 #include <ctype.h>
 #include <string.h>
 
-static void
+static inline void
 reset(struct Token *t)
 {
 	t->token = nullptr;
@@ -48,9 +48,7 @@ parse_next(const char *buf, const size_t length, size_t *offset,
 {
 	size_t	 cursor = *offset;
 
-	// Clear the token.
 	reset(token);
-
 	if (cursor == length) {
 		return PARSE_EOB;
 	}
diff --git a/stack.h b/stack.h
index 849b710..a4f31a8 100644
--- a/stack.h
+++ b/stack.h
@@ -9,6 +9,7 @@ public:
         bool   push(T val);
 	bool   pop(T *val);
 	bool   get(size_t, T &);
+	bool   remove(size_t, T *);
 	size_t size(void) { return this->arrlen; }
 	void   clear(void) { this->arrlen = 0; }
 private:
@@ -56,4 +57,21 @@ Stack<T>::get(size_t i, T &val)
 	return true;
 }
 
+// remove returns false on invalid bounds
+template <typename T>
+bool
+Stack<T>::remove(size_t i, T *val)
+{
+	if (i > this->arrlen) {
+		return false;
+	}
+
+	*val = this->arr[i];
+	for (; i < (arrlen - 1); i++) {
+		this->arr[i] = this->arr[i+1];
+	}
+	arrlen--;
+	return true;
+}
+
 #endif // __KF_STACK_H__
\ No newline at end of file
diff --git a/system.cc b/system.cc
new file mode 100644
index 0000000..aebd834
--- /dev/null
+++ b/system.cc
@@ -0,0 +1,64 @@
+#include "defs.h"
+#include "system.h"
+
+#include <string.h>
+
+constexpr static char	STATE_STR_OK[] = "ok";
+constexpr static char   STATE_STR_STACK_OVERFLOW[] = "stack overflow";
+constexpr static char   STATE_STR_STACK_UNDERFLOW[] = "stack underflow";
+constexpr static char   STATE_STR_EXECUTION_FAILURE[] = "execution failure";
+constexpr static char	STATE_STR_UNKNOWN_WORD[] = "unknown word";
+constexpr static char	STATE_STR_UNKNOWN_STATE[] = "undefined state";
+constexpr static char	STATE_STR_ERROR_CODE[] = " (error code ";
+
+void
+system_clear_error(System *sys)
+{
+	sys->status = STATUS_OK;
+}
+
+void
+system_write_status(System *sys)
+{
+	char	*buf = nullptr;
+	size_t	 len = 0;
+
+	if (sys->interface == nullptr) {
+		return;
+	}
+	
+	switch (sys->status) {
+	case STATUS_OK:
+		buf = (char *)(STATE_STR_OK);
+		len = sizeof STATE_STR_OK;
+		break;
+	case STATUS_STACK_OVERFLOW:
+		buf = (char *)(STATE_STR_STACK_OVERFLOW);
+		len = sizeof STATE_STR_STACK_OVERFLOW;
+		break;
+	case STATUS_STACK_UNDERFLOW:
+		buf = (char *)(STATE_STR_STACK_UNDERFLOW);
+		len = sizeof STATE_STR_STACK_UNDERFLOW;
+		break;
+	case STATUS_EXECUTION_FAILURE:
+		buf = (char *)(STATE_STR_EXECUTION_FAILURE);
+		len = sizeof STATE_STR_EXECUTION_FAILURE;
+		break;
+	case STATUS_UNKNOWN_WORD:
+		buf = (char *)(STATE_STR_UNKNOWN_WORD);
+		len = sizeof STATE_STR_UNKNOWN_WORD;
+		break;
+	default:
+		buf = (char *)(STATE_STR_UNKNOWN_STATE);
+		len = sizeof STATE_STR_UNKNOWN_STATE;
+		break;
+	}
+	
+	sys->interface->wrbuf(buf, len);
+	if (sys->status != STATUS_OK) {
+		sys->interface->wrbuf((char *)STATE_STR_ERROR_CODE, sizeof STATE_STR_ERROR_CODE);
+		write_num(sys->interface, (KF_INT)sys->status);
+		sys->interface->wrch(')');
+	}
+	sys->interface->wrch('.');
+}
\ No newline at end of file
diff --git a/system.h b/system.h
index 00f4a34..91aa1fa 100644
--- a/system.h
+++ b/system.h
@@ -5,11 +5,24 @@
 #include "io.h"
 #include "stack.h"
 
+typedef enum _SYS_STATUS : uint8_t {
+	STATUS_OK = 0,
+	STATUS_STACK_OVERFLOW = 1,
+	STATUS_STACK_UNDERFLOW = 2,
+	STATUS_EXECUTION_FAILURE = 3,
+	STATUS_UNKNOWN_WORD = 4
+} SYS_STATUS;
+
+class Word;
+
 typedef struct _System {
 	Stack<KF_INT>	 dstack;
 	IO		*interface;
-	struct Word	*dict;
+	Word		*dict;
+	SYS_STATUS	 status;
 } System;
 
+void	system_clear_error(System *sys);
+void	system_write_status(System *sys);
 
 #endif // __KF_CORE_H__
\ No newline at end of file