diff --git a/Makefile b/Makefile
index 6b15ec0..4a09afc 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,8 @@ CXXFLAGS :=	-std=$(CXXSTD) -Wall -Werror -g -O0
 OBJS :=		linux/io.o	\
 		io.o		\
 		parser.o	\
+		word.o		\
+		dict.o		\
 		kforth.o
 TARGET :=	kforth
 
@@ -13,3 +15,7 @@ $(TARGET): $(OBJS)
 
 clean:
 	rm -f $(OBJS) $(TARGET)
+
+install: $(TARGET)
+	cp $(TARGET) ~/bin
+	chmod 0755 ~/bin/$(TARGET)
diff --git a/dict.cc b/dict.cc
new file mode 100644
index 0000000..53ad8cd
--- /dev/null
+++ b/dict.cc
@@ -0,0 +1,178 @@
+#include "defs.h"
+#include "dict.h"
+#include "stack.h"
+#include "system.h"
+#include "word.h"
+
+static bool
+add(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	a += b;
+	return sys->dstack.push(a);
+}
+
+static bool
+sub(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	b -= a;
+	return sys->dstack.push(b);
+}
+
+static bool
+mul(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	b *= a;
+	return sys->dstack.push(b);
+}
+
+static bool
+div(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	b *= a;
+	return sys->dstack.push(b);
+}
+
+static bool
+swap(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		return false;
+	}
+	
+	return sys->dstack.push(b);
+}
+
+static bool
+rot(System *sys)
+{
+	KF_INT	a = 0;
+	KF_INT	b = 0;
+	KF_INT	c = 0;
+	if (!sys->dstack.pop(&a)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&b)) {
+		return false;
+	}
+	
+	if (!sys->dstack.pop(&c)) {
+		return false;
+	}
+	
+	if (!sys->dstack.push(b)) {
+		return false;
+	}
+	
+	if (!sys->dstack.push(a)) {
+		return false;
+	}
+	
+	return sys->dstack.push(c);
+}
+
+// TODO: print multiple per line
+static bool
+definitions(System *sys)
+{
+	Word	*cursor = dict;
+	char	 buf[MAX_TOKEN_LENGTH];
+	size_t	 buflen = 0;
+	
+	while (cursor != nullptr) {
+		cursor->getname(buf, &buflen);
+		sys->interface->wrln(buf, buflen);
+		cursor = cursor->next();
+	}
+	
+	return true;
+}
+
+void
+init_dict()
+{
+	dict = new Builtin((const char *)"DEFINITIONS", 11, dict, definitions);
+	dict = new Builtin((const char *)"+", 1, dict, add);
+	dict = new Builtin((const char *)"-", 1, dict, sub);
+	dict = new Builtin((const char *)"*", 1, dict, mul);
+	dict = new Builtin((const char *)"/", 1, dict, div);
+	dict = new Builtin((const char *)"SWAP", 4, dict, swap);
+	dict = new Builtin((const char *)"ROT", 3, dict, rot);
+}
+
+
+LOOKUP
+lookup(struct Token *token, System *sys)
+{
+	Word	*cursor = dict;
+	KF_INT	 n;
+	
+	if (parse_num(token, &n)) {
+		if (sys->dstack.push(n)) {
+			return LOOKUP_OK;
+		}
+		return LOOKUP_FAILED;
+	}
+	
+	while (cursor != nullptr) {
+		if (cursor->match(token)) {
+			if (cursor->eval(sys)) {
+				return LOOKUP_OK;
+			}
+			return LOOKUP_FAILED;
+		}
+		cursor = cursor->next();
+	}
+	
+	return LOOKUP_NOTFOUND;
+}
\ No newline at end of file
diff --git a/dict.h b/dict.h
new file mode 100644
index 0000000..c63181b
--- /dev/null
+++ b/dict.h
@@ -0,0 +1,22 @@
+#ifndef __KF_DICT_H__
+#define __KF_DICT_H__
+
+#include "defs.h"
+#include "parser.h"
+#include "system.h"
+#include "word.h"
+
+static	Word	*dict = nullptr;
+
+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(void);
+LOOKUP	lookup(struct Token *, System *);
+
+
+
+#endif // __KF_DICT_H__
\ No newline at end of file
diff --git a/doc/index.rst b/doc/index.rst
index d313229..08a7242 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -10,6 +10,7 @@ Contents:
    part-0x02
    part-0x03
    part-0x04
+   part-0x05
 
 Indices and tables
 ==================
diff --git a/doc/part-0x05.rst b/doc/part-0x05.rst
new file mode 100644
index 0000000..f2e0193
--- /dev/null
+++ b/doc/part-0x05.rst
@@ -0,0 +1,46 @@
+Write You a Forth, 0x05
+-----------------------
+
+:date: 2018-02-24 12:23
+:tags: wyaf, forth
+
+Today I need to start actually doing things with tokens. This requires two
+things:
+
+1. Some idea of what a word is, and
+2. A dictionary of words
+
+I started taking some notes on this previously, and I think there are a few
+kinds of words that are possible:
+
+1. Numbers (e.g. defining a variable)
+2. Built-in functions
+3. Lambda functions (that is, user-defined functions).
+
+Stage 1 really only needs to incorporate #2, so that's what I'll focus on for
+now. However, to prepare for the future, I'm going to define a ``Word`` base
+class and inherit from there. This interface is going to need to be
+stack-aware, so what I've done is define a ``System`` struct in ``system.h``::
+
+        #ifndef __KF_CORE_H__
+        #define __KF_CORE_H__
+        
+        #include "defs.h"
+        #include "stack.h"
+        
+        typedef struct _System {
+                Stack<KF_INT>        dstack;
+        } System;
+        
+        
+        #endif // __KF_CORE_H__
+
+This will let me later add in support for the return stack and other things
+that might be useful. Other ideas: adding something like an ``errno``
+equivalent to indicate the last error, and storing a dictionary of words. This
+will need some restructuring, though. Anyways, this works for now.
+
+The Word interface
+^^^^^^^^^^^^^^^^^^
+
+Now I can start defining a Word.h.
\ No newline at end of file
diff --git a/io.cc b/io.cc
index a4d70b8..77e0e2a 100644
--- a/io.cc
+++ b/io.cc
@@ -6,7 +6,7 @@
 static constexpr size_t	nbuflen = 11;
 
 void
-write_num(IO &interface, KF_INT n)
+write_num(IO *interface, KF_INT n)
 {
 
 	// TODO(kyle): make the size of the buffer depend on the size of
@@ -17,8 +17,12 @@ write_num(IO &interface, KF_INT n)
 	bool neg = n < 0;
 
 	if (n < 0) {
-		interface.wrch('-');
+		interface->wrch('-');
 		n = ~n;
+		if (n == 0) {
+			neg = false;
+			n++;
+		}
 	}
 
 	while (n != 0) {
@@ -30,5 +34,5 @@ write_num(IO &interface, KF_INT n)
 	}
 
 	uint8_t buflen = nbuflen - i % nbuflen;
-	interface.wrbuf(buf+i, buflen);
+	interface->wrbuf(buf+i, buflen);
 }
\ No newline at end of file
diff --git a/io.h b/io.h
index 4f957a6..38bf51b 100644
--- a/io.h
+++ b/io.h
@@ -21,7 +21,7 @@ public:
 	virtual void	wrln(char *buf, size_t len) = 0;
 };
 
-void	write_num(IO &, KF_INT);
+void	write_num(IO *, KF_INT);
 
 
 #endif // __KF_IO_H__
\ No newline at end of file
diff --git a/kforth.cc b/kforth.cc
index 77c7320..10d8aa2 100644
--- a/kforth.cc
+++ b/kforth.cc
@@ -1,6 +1,7 @@
+#include "dict.h"
 #include "io.h"
 #include "parser.h"
-#include "stack.h"
+#include "system.h"
 
 #include <stdlib.h>
 #include <string.h>
@@ -11,33 +12,33 @@
 
 static char     ok[] = "ok.\n";
 static char	bye[] = "bye";
-
-// dstack is the data stack.
-static Stack<KF_INT>	dstack;
+static System	sys;
 
 
 static void
-write_dstack(IO &interface)
+write_dstack()
 {
 	KF_INT	tmp;
-	interface.wrch('<');
-	for (size_t i = 0; i < dstack.size(); i++) {
+	sys.interface->wrch('<');
+	for (size_t i = 0; i < sys.dstack.size(); i++) {
 		if (i > 0) {
-			interface.wrch(' ');
+			sys.interface->wrch(' ');
 		}
 
-		dstack.get(i, tmp);
-		write_num(interface, tmp);
+		sys.dstack.get(i, tmp);
+		write_num(sys.interface, tmp);
 	}
-	interface.wrch('>');
+	sys.interface->wrch('>');
 }
 
 static bool
-parser(IO &interface, const char *buf, const size_t buflen)
+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;
 
@@ -46,50 +47,66 @@ parser(IO &interface, const char *buf, const size_t buflen)
 	token.length = 0;
 
 	while ((result = parse_next(buf, buflen, &offset, &token)) == PARSE_OK) {
-		interface.wrbuf((char *)"token: ", 7);
-		interface.wrbuf(token.token, token.length);
-		interface.wrln((char *)".", 1);
-
-		if (!parse_num(&token, dstack)) {
-			interface.wrln((char *)"failed to parse numeric", 23);
+		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;
+			break;
+		}
+		
 		// Temporary hack until the interpreter is working further.
 		if (match_token(token.token, token.length, bye, 3)) {
-			interface.wrln((char *)"Goodbye!", 8);
+			sys.interface->wrln((char *)"Goodbye!", 8);
 			exit(0);
 		}
 	}
 
 	switch (result) {
+	case PARSE_OK:
+		return false;
 	case PARSE_EOB:
-		interface.wrbuf(ok, 4);
+		sys.interface->wrbuf(ok, 4);
 		return true;
 	case PARSE_LEN:
-		interface.wrln((char *)"parse error: token too long", 27);
+		sys.interface->wrln((char *)"parse error: token too long", 27);
 		return false;
 	case PARSE_FAIL:
-		interface.wrln((char *)"parser failure", 14);
+		sys.interface->wrln((char *)"parser failure", 14);
 		return false;
 	default:
-		interface.wrln((char *)"*** the world is broken ***", 27);
+		sys.interface->wrln((char *)"*** the world is broken ***", 27);
 		exit(1);
 	}
 }
 
 static void
-interpreter(IO &interface)
+interpreter()
 {
 	static size_t buflen = 0;
 	static char linebuf[81];
 
 	while (true) {
-		write_dstack(interface);
-		interface.wrch('\n');
-		interface.wrch('?');
-		interface.wrch(' ');
-		buflen = interface.rdbuf(linebuf, 80, true, '\n');
-		parser(interface, linebuf, buflen);
+		write_dstack();
+		sys.interface->wrch('\n');
+		sys.interface->wrch('?');
+		sys.interface->wrch(' ');
+		buflen = sys.interface->rdbuf(linebuf, 80, true, '\n');
+		parser(linebuf, buflen);
 	}
 }
 
@@ -99,10 +116,12 @@ const size_t	bannerlen = 19;
 int
 main(void)
 {
+	init_dict();
 #ifdef __linux__
 	Console interface;
+	sys.interface = &interface;
 #endif
-	interface.wrbuf(banner, bannerlen);
-	interpreter(interface);
+	sys.interface->wrbuf(banner, bannerlen);
+	interpreter();
 	return 0;
 }
\ No newline at end of file
diff --git a/linux/io.cc b/linux/io.cc
index aeef8bb..51015e1 100644
--- a/linux/io.cc
+++ b/linux/io.cc
@@ -25,6 +25,9 @@ Console::rdbuf(char *buf, size_t len, bool stopat, char stopch)
 
 	while (n < len) {
 		ch = this->rdch();
+		if (ch == 0x04) {
+			break;
+		}
 
 		if (stopat && stopch == ch) {
 			break;
diff --git a/parser.cc b/parser.cc
index 6a94687..f7e35f4 100644
--- a/parser.cc
+++ b/parser.cc
@@ -19,7 +19,22 @@ match_token(const char *a, const size_t alen,
 		return false;
 	}
 
-	return memcmp(a, b, alen) == 0;
+	for (size_t i = 0; i < alen; i++) {
+		if (a[i] == b[i]) {
+			continue;
+		}
+		
+		if ((a[i] ^ 0x20) == b[i]) {
+			continue;
+		}
+		
+		if (a[i] == (b[i] ^ 0x20)) {
+			continue;
+		}
+		
+		return false;
+	}
+	return true;
 }
 
 PARSE_RESULT
@@ -72,9 +87,9 @@ parse_next(const char *buf, const size_t length, size_t *offset,
 }
 
 bool
-parse_num(struct Token *token, Stack<KF_INT> &s)
+parse_num(struct Token *token, KF_INT *n)
 {
-	KF_INT	n = 0;
+	KF_INT	tmp = 0;
 	uint8_t i = 0;
 	bool    sign = false;
 
@@ -83,6 +98,9 @@ parse_num(struct Token *token, Stack<KF_INT> &s)
 	}
 
 	if (token->token[i] == '-') {
+		if (token->length == 1) {
+			return false;
+		}
 		i++;
 		sign = true;
 	}
@@ -96,14 +114,15 @@ parse_num(struct Token *token, Stack<KF_INT> &s)
 			return false;
 		}
 
-		n *= 10;
-		n += (uint8_t)(token->token[i] - '0');
+		tmp *= 10;
+		tmp += (uint8_t)(token->token[i] - '0');
 		i++;
 	}
 
 	if (sign) {
-		n *= -1;
+		tmp *= -1;
 	}
 
-	return s.push(n);
+	*n = tmp;
+	return true;
 }
\ No newline at end of file
diff --git a/parser.h b/parser.h
index 4cdef1d..af2f5a7 100644
--- a/parser.h
+++ b/parser.h
@@ -21,7 +21,7 @@ PARSE_RESULT	parse_next(const char *, const size_t, size_t *, struct Token *);
 
 // TODO(kyle): investigate a better return value, e.g. to differentiate between
 // stack failures and parse failures.
-bool		parse_num(struct Token *, Stack<KF_INT> &);
+bool		parse_num(struct Token *, KF_INT *);
 
 
 #endif // __KF_PARSER_H__
diff --git a/stack.h b/stack.h
index e23fe9a..849b710 100644
--- a/stack.h
+++ b/stack.h
@@ -7,9 +7,10 @@ template <typename T>
 class Stack {
 public:
         bool   push(T val);
-	bool   pop(T &val);
+	bool   pop(T *val);
 	bool   get(size_t, T &);
-	size_t size(void) { return this->arrlen; };
+	size_t size(void) { return this->arrlen; }
+	void   clear(void) { this->arrlen = 0; }
 private:
 	T arr[STACK_SIZE];
 	size_t arrlen;
@@ -31,14 +32,15 @@ Stack<T>::push(T val)
 // pop returns false if there was a stack underflow.
 template <typename T>
 bool
-Stack<T>::pop(T &val)
+Stack<T>::pop(T *val)
 {
 	if (this->arrlen == 0) {
 		return false;
 	}
 
-	val = this->arr[this->arrlen - 1];
+	*val = this->arr[this->arrlen - 1];
 	this->arrlen--;
+	return true;
 }
 
 // get returns false on invalid bounds.
diff --git a/system.h b/system.h
new file mode 100644
index 0000000..77413d3
--- /dev/null
+++ b/system.h
@@ -0,0 +1,14 @@
+#ifndef __KF_CORE_H__
+#define __KF_CORE_H__
+
+#include "defs.h"
+#include "io.h"
+#include "stack.h"
+
+typedef struct _System {
+	Stack<KF_INT>	 dstack;
+	IO		*interface;
+} System;
+
+
+#endif // __KF_CORE_H__
\ No newline at end of file
diff --git a/word.cc b/word.cc
new file mode 100644
index 0000000..399b275
--- /dev/null
+++ b/word.cc
@@ -0,0 +1,39 @@
+#include "defs.h"
+#include "parser.h"
+#include "system.h"
+#include "word.h"
+
+#include <string.h>
+
+
+Builtin::Builtin(const char *name, size_t namelen, Word *head, bool (*target)(System *))
+	: prev(head), fun(target)
+{
+	memcpy(this->name, name, namelen);
+	this->namelen = namelen;
+}
+	
+bool
+Builtin::eval(System *sys)
+{
+	return this->fun(sys);
+}
+
+Word *
+Builtin::next()
+{
+	return this->prev;
+}
+	
+bool
+Builtin::match(struct Token *token)
+{
+	return match_token(this->name, this->namelen, token->token, token->length);
+}
+
+void
+Builtin::getname(char *buf, size_t *buflen)
+{
+	memcpy(buf, this->name, this->namelen);
+	*buflen = namelen;
+}
\ No newline at end of file
diff --git a/word.h b/word.h
new file mode 100644
index 0000000..84b7684
--- /dev/null
+++ b/word.h
@@ -0,0 +1,37 @@
+#ifndef __KF_WORD_H__
+#define __KF_WORD_H__
+
+#include "defs.h"
+#include "parser.h"
+#include "stack.h"
+#include "system.h"
+
+class Word {
+public:
+	virtual ~Word() {};
+
+	virtual bool  eval(System *) = 0;
+	virtual Word *next(void) = 0;
+	virtual bool  match(struct Token *) = 0;
+	virtual void  getname(char *, size_t *) = 0;
+};
+
+class Builtin : public Word {
+public:
+	~Builtin() {};
+	Builtin(const char *name, size_t namelen, Word *head, bool (*fun)(System *));
+	
+	bool  eval(System *);
+	Word *next(void);
+	bool  match(struct Token *);
+	void  getname(char *, size_t *);
+	
+private:
+	char		 name[MAX_TOKEN_LENGTH];
+	size_t		 namelen;
+	Word		*prev;
+	bool		(*fun)(System *);
+};
+
+
+#endif // __KF_WORD_H__
\ No newline at end of file