diff --git a/.clangd b/.clangd
index bf16b8a..8441862 100644
--- a/.clangd
+++ b/.clangd
@@ -6,7 +6,8 @@ CompileFlags:
       -Wpedantic,
       -xc,
       -D_POSIX_C_SOURCE=199309L,
-      "-fsanitize=address,undefined",
+      "-Isrc",
+      "-I../",
     ]
   Compiler: gcc
 ---
@@ -14,8 +15,7 @@ If:
   PathMatch: .*\.h
 CompileFlags:
   Remove: -xc
-  Add: [-std=c11, -Wall, -Wpedantic, -xc-header]
-  Compiler: gcc
+  Add: -xc-header
 ---
 If:
   PathMatch: bin/.*\.c
diff --git a/Makefile b/Makefile
index c9e2e73..e096bcb 100644
--- a/Makefile
+++ b/Makefile
@@ -19,7 +19,7 @@ CFLAGS=$(DEBUG_CFLAGS) $(LLVM_SAN_FLAGS) -std=c11 -Wall -Wpedantic $\
 LD=gcc
 LDFLAGS=$(LLVM_SAN_FLAGS)
 
-SRCS:=$(wildcard src/*.c)
+SRCS:=$(wildcard src/*.c) $(wildcard src/byterun/*.c)
 OBJS:=$(SRCS:src/%.c=bin/%.o)
 DEPS:=$(SRCS:src/%.c=bin/deps/%.d)
 
@@ -34,12 +34,11 @@ glisp: $(OBJS)
 	$(LD) $(LDFLAGS) -o $@ $^
 
 bin/init_globals.c: $(filter-out bin/init_globals.c,$(SRCS_WITH_HEADERS)) src/gen-init-globals.awk
-	@mkdir -p bin/
 	awk -f src/gen-init-globals.awk $(filter-out src/gen-init-globals.awk,$^) >$@
 
 bin/%.o: src/%.c
-	@mkdir -p bin/deps
-	$(CC) $(CFLAGS) -c -MMD -MF $(<:src/%.c=bin/deps/%.d) -o $@ $<
+	@mkdir -p $(dir $(<:src/%.c=bin/deps/%.d) $(<:src/%.c=bin/%))
+	$(CC) $(CFLAGS) -c -MMD -MF $(<:src/%.c=bin/deps/%.d) -I src/ -o $@ $<
 
 bin/init_globals.o: bin/init_globals.c
 	@mkdir -p bin/deps
diff --git a/src/base.h b/src/base.h
index 9e699a8..3d83446 100644
--- a/src/base.h
+++ b/src/base.h
@@ -76,15 +76,16 @@ static ALWAYS_INLINE LispVal *MAKE_LISP_FLOAT(lisp_float_t flt) {
 // ###############
 // # Other types #
 // ###############
+// Make sure this is kept up to date with byterun.h
 typedef enum {
-    TYPE_FIXNUM,
-    TYPE_FLOAT,
-    TYPE_CONS,
-    TYPE_STRING,
-    TYPE_SYMBOL,
-    TYPE_VECTOR,
-    TYPE_HASH_TABLE,
-    TYPE_FUNCTION,
+    TYPE_FIXNUM = 0,
+    TYPE_FLOAT = 1,
+    TYPE_CONS = 2,
+    TYPE_STRING = 3,
+    TYPE_SYMBOL = 4,
+    TYPE_VECTOR = 5,
+    TYPE_HASH_TABLE = 6,
+    TYPE_FUNCTION = 7,
     N_LISP_TYPES,
 } LispValType;
 extern const char *LISP_TYPE_NAMES[N_LISP_TYPES];
diff --git a/src/byterun/BYTECODE.md b/src/byterun/BYTECODE.md
new file mode 100644
index 0000000..44c7664
--- /dev/null
+++ b/src/byterun/BYTECODE.md
@@ -0,0 +1,59 @@
+The bytecode interpreter runs using a stack. Most instructions operate on the
+stack. Each instruction starts with a 1 byte opcode. If it has arguments, they
+come next (and are detailed below). All functions push their return value onto
+the stack (though some produce no return value).
+
+The leftmost (most significant) bit of the opcode is the "save flag" if it is
+set, the instruction does not remove its arguments from the stack.
+
+Each block of bytecode (function, etc.) starts with some constants. They have
+the following format
+
+WORDSIZE bytes - Number of constants
+NOTE: in the below MINSIZE is the minimum number of bytes needed to reach any
+object, signed.
+The constants start with 1 byte for type (as in base.h). Their formats follow:
+FIXNUM: WORDSIZE bytes (for the value with the tag already set).
+FLOAT: WORDSIZE bytes (for the value with the tag already set).
+CONS: two MINSIZE bytes fields for the car and cdr.
+STRING: WORDSIZE bytes for the length, then the bytes themselves.
+SYMBOL: WORDSIZE bytes for the length, then the bytes themselves. These are for
+the name. The VM interns the symbol when it loads the bytecode.
+VECTOR: WORDSIZE bytes for the length. Then MINSIZE bytes for each element.
+HASH_TABLE: Not a valid constant
+FUNCTION: TODO - Not implemented yet (this will include lambdas).
+LIST (Type code is FUNCTION + 1): Ditto vector, but a list is created
+instead. This is just a convenience.
+
+Instructions (Name - Opcode):
+
+NIL - 0x0: Push nil onto the stack.
+
+CONS - 0x1: Return a cons of the top of the stack. The top becomes the cdr and
+the next element the car.
+
+CAR - 0x2: Return the car of the cons on top of the stack.
+
+CDR - 0x3: Return the cdr of the cons on top of the stack.
+
+NULL - 0x4: Return t if the top if the stack is nil, otherwise return nil.
+
+POP - 0x5: Throw away the top of the stack (produces no value). Doing this with
+the save flag set is a noop.
+
+COPY - 0x6: Takes one argument which is a zero-indexed offset from the top of
+the stack (as in 0 is the top). Pushes a copy of the element onto the top of the
+stack.
+
+LOAD - 0x7: Load the constant numbered onto the top of the stack. This takes no
+stack arguments. It takes one constant argument (which is the smallest width
+necessary to load all constants). This argument is simply a number.
+
+EQ - 0x8: If the top two elements of the stack are the same, object, return t,
+otherwise return nil.
+
+FUNCALL - 0x9: Call the function on top of the stack. The second argument is the
+number of arguments. That many elements are then used as the arguments. The
+first argument is the one directly following the count.
+
+PRINT - 0x7f: DEBUG ONLY - print the top of the stack
diff --git a/src/byterun/assemble.c b/src/byterun/assemble.c
new file mode 100644
index 0000000..eda2882
--- /dev/null
+++ b/src/byterun/assemble.c
@@ -0,0 +1,210 @@
+#include "assemble.h"
+
+#include "base.h"
+#include "memory.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdbool.h>
+#include <strings.h>
+
+BytecodeOpcode bytecode_opcode_by_name(const char *name, size_t length) {
+    struct Bucket {
+        size_t name_len;
+        const char *name;
+        BytecodeOpcode opcode;
+        struct Bucket *next;
+    };
+    static struct Bucket *TABLE[26] = {NULL};
+    static bool did_init = false;
+    if (!did_init) {
+#define PUT(mname)                                             \
+    {                                                          \
+        struct Bucket *n = lisp_malloc(sizeof(struct Bucket)); \
+        n->name_len = sizeof(#mname) - 1;                      \
+        n->name = #mname;                                      \
+        n->opcode = BO_##mname;                                \
+        size_t hash = tolower(#mname[0]) - 'a';                \
+        n->next = TABLE[hash];                                 \
+        TABLE[hash] = n;                                       \
+    }
+        PUT(NIL);
+        PUT(CONS);
+        PUT(CAR);
+        PUT(CDR);
+        PUT(NULL);
+        PUT(POP);
+        PUT(COPY);
+        PUT(LOAD);
+        PUT(EQ);
+        PUT(FUNCALL);
+        PUT(PRINT);
+#undef PUT
+        did_init = true;
+    }
+    if (!length) {
+        return BO_INVALID;
+    }
+    size_t hash = tolower(name[0]) - 'a';
+    assert(0 <= hash && hash <= 25);
+    for (struct Bucket *cur = TABLE[hash]; cur; cur = cur->next) {
+        if (cur->name_len == length && strcasecmp(cur->name, name) == 0) {
+            return cur->opcode;
+        }
+    }
+    return BO_INVALID;
+}
+
+const char *bytecode_opcode_name(BytecodeOpcode opcode, size_t *length) {
+#define DEF(name)                        \
+    case BO_##name:                      \
+        if (length) {                    \
+            *length = sizeof(#name) - 1; \
+        }                                \
+        return #name
+    switch (opcode) {
+        DEF(NIL);
+        DEF(CONS);
+        DEF(CAR);
+        DEF(CDR);
+        DEF(NULL);
+        DEF(POP);
+        DEF(COPY);
+        DEF(LOAD);
+        DEF(EQ);
+        DEF(FUNCALL);
+        DEF(PRINT);
+    case BO_INVALID:
+        return NULL;
+    default:
+        abort();
+    }
+#undef DEF
+}
+
+BytecodeConstType bytecode_const_type_by_name(const char *name, size_t length) {
+#define CHECK(type)                   \
+    if (strcasecmp(name, #type)) {    \
+        return BYTECODE_CONST_##type; \
+    }
+    CHECK(FIXNUM);
+    CHECK(FLOAT);
+    CHECK(CONS);
+    CHECK(STRING);
+    CHECK(SYMBOL);
+    CHECK(VECTOR);
+    CHECK(FUNCTION);
+    CHECK(LIST);
+    return BYTECODE_CONST_INVALID;
+#undef CHECK
+}
+
+const char *bytecode_const_name(BytecodeConstType type, size_t *length) {
+#define DEF(name)                        \
+    case BYTECODE_CONST_##name:          \
+        if (length) {                    \
+            *length = sizeof(#name) - 1; \
+        }                                \
+        return #name;
+    switch (type) {
+        DEF(FIXNUM);
+        DEF(FLOAT);
+        DEF(CONS);
+        DEF(STRING);
+        DEF(SYMBOL);
+        DEF(VECTOR);
+        DEF(FUNCTION);
+        DEF(LIST);
+    case BO_INVALID:
+        return NULL;
+    default:
+        abort();
+    }
+}
+
+enum AssembleMode { MODE_NONE, MODE_CONSTANTS, MODE_TEXT };
+
+typedef struct {
+    BytecodeConstType type;
+    union {
+        fixnum_t fixnum;
+        lisp_float_t lisp_float;
+        struct {
+            intptr_t car;
+            intptr_t cdr;
+        } cons;
+        struct {
+            size_t length;
+            const char *bytes;
+        } string;
+        struct {
+            size_t length;
+            const char *bytes;
+        } symbol;
+        struct {
+            size_t length;
+            intptr_t elements;
+        } vector;
+        struct {
+            // TODO implement
+            int dummy;
+        } function;
+        struct {
+            size_t length;
+            intptr_t elements;
+        } list;
+    };
+} AssembleConstant;
+
+struct AssembleState {
+    enum AssembleMode mode;
+    size_t line_no;
+
+    size_t num_constants;
+    AssembleConstant *constants;
+    size_t num_instructions;
+};
+
+static bool is_blank_string(const char *data, size_t len) {
+    for (size_t i = 0; i < len; ++i) {
+        if (data[i] != ' ' && data[i] != '\t') {
+            return false;
+        }
+    }
+    return true;
+}
+
+static BytecodeAssembleStatus
+process_line_none_mode(struct AssembleState *restrict state,
+                       const size_t line_len, const char line[line_len],
+                       BytecodeAssembleError *restrict error) {}
+
+BytecodeAssembleStatus
+bytecode_assemble(const size_t src_length, const char src[src_length],
+                  size_t *restrict out_length, char **restrict out,
+                  BytecodeAssembleError *restrict error) {
+    StringStream stream;
+    string_stream_init(&stream);
+    struct AssembleState state = {
+        .mode = MODE_NONE,
+        .line_no = 1,
+        .num_constants = 0,
+        .constants = NULL,
+        .num_instructions = 0,
+    };
+    const char *line = NULL;
+    size_t line_len;
+    while (strgetline(src, src_length, &line, &line_len)) {
+        switch (state.mode) {
+        case MODE_NONE:
+            process_line_none_mode(&state, line_len, line, error);
+            break;
+        case MODE_CONSTANTS:
+        case MODE_TEXT:
+            break;
+        }
+        ++state.line_no;
+    }
+    string_stream_steal(&stream, out, out_length);
+    return BYTECODE_ASSEMBLE_OK;
+}
diff --git a/src/byterun/assemble.h b/src/byterun/assemble.h
new file mode 100644
index 0000000..d6d8a48
--- /dev/null
+++ b/src/byterun/assemble.h
@@ -0,0 +1,32 @@
+#ifndef INCLUDED_ASSEMBLE_H
+#define INCLUDED_ASSEMBLE_H
+
+#include "byterun.h"
+
+#include <stddef.h>
+
+BytecodeOpcode bytecode_opcode_by_name(const char *name, size_t length);
+const char *bytecode_opcode_name(BytecodeOpcode opcode, size_t *length);
+
+BytecodeConstType bytecode_const_type_by_name(const char *name, size_t length);
+const char *bytecode_const_name(BytecodeConstType type, size_t *length);
+
+typedef enum {
+    BYTECODE_ASSEMBLE_OK,
+    BYTECODE_ASSEMBLE_SYNTAX,
+} BytecodeAssembleStatus;
+
+typedef struct {
+    size_t line;
+    size_t col;
+    size_t length;
+    const char *detail;
+} BytecodeAssembleError;
+
+BytecodeAssembleStatus bytecode_assemble(const size_t src_length,
+                                         const char src[src_length],
+                                         size_t *restrict out_length,
+                                         char **restrict out,
+                                         BytecodeAssembleError *restrict error);
+
+#endif
diff --git a/src/byterun/byterun.c b/src/byterun/byterun.c
new file mode 100644
index 0000000..267d70e
--- /dev/null
+++ b/src/byterun/byterun.c
@@ -0,0 +1 @@
+#include "byterun.h"
diff --git a/src/byterun/byterun.h b/src/byterun/byterun.h
new file mode 100644
index 0000000..59c70d5
--- /dev/null
+++ b/src/byterun/byterun.h
@@ -0,0 +1,33 @@
+#ifndef INCLUDED_BYTERUN_H
+#define INCLUDED_BYTERUN_H
+
+typedef enum {
+    BO_NIL = 0x00,
+    BO_CONS = 0x01,
+    BO_CAR = 0x02,
+    BO_CDR = 0x03,
+    BO_NULL = 0x04,
+    BO_POP = 0x05,
+    BO_COPY = 0x06,
+    BO_LOAD = 0x07,
+    BO_EQ = 0x08,
+    BO_FUNCALL = 0x09,
+    BO_PRINT = 0x7f,
+    BO_INVALID = 0xff,
+} BytecodeOpcode;
+
+// make sure this is kept up to date with base.h
+typedef enum {
+    BYTECODE_CONST_FIXNUM = 0,
+    BYTECODE_CONST_FLOAT = 1,
+    BYTECODE_CONST_CONS = 2,
+    BYTECODE_CONST_STRING = 3,
+    BYTECODE_CONST_SYMBOL = 4,
+    BYTECODE_CONST_VECTOR = 5,
+    // So such constant BYTECODE_CONST_HASH_TABLE = 6,
+    BYTECODE_CONST_FUNCTION = 7,
+    BYTECODE_CONST_LIST = 8,
+    BYTECODE_CONST_INVALID = 0xff,
+} BytecodeConstType;
+
+#endif
diff --git a/src/gc.h b/src/gc.h
index 3136090..2be5c16 100644
--- a/src/gc.h
+++ b/src/gc.h
@@ -67,7 +67,7 @@ void lisp_gc_register_static_object(void *val);
 void gc_move_to_set(void *val, ObjectGCSet new_set);
 
 // note that the argument is restrict!
-void lisp_gc_now(LispGCStats *restrict status);
+void lisp_gc_now(LispGCStats *restrict stats);
 
 // Debug
 void debug_print_gc_stats(FILE *stream, const LispGCStats *stats);
diff --git a/src/main.c b/src/main.c
index ef4eadf..8ece9d7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,30 +1,36 @@
+#include "byterun/assemble.h"
 #include "lisp.h"
 #include "read.h"
 
 #include <stdio.h>
 
-DEFUN(cool_func, "cool-func", (LispVal * a, LispVal *b), "(a &optional b)",
-      "") {
-    printf("A: ");
-    debug_obj_info(stdout, a);
-    printf("B: ");
-    debug_obj_info(stdout, b);
-    return Qnil;
-}
+/* DEFUN(cool_func, "cool-func", (LispVal * a, LispVal *b), "(a &optional b)",
+ */
+/*       "") { */
+/*     printf("A: "); */
+/*     debug_obj_info(stdout, a); */
+/*     printf("B: "); */
+/*     debug_obj_info(stdout, b); */
+/*     return Qnil; */
+/* } */
 
-int main(int argc, const char **argv) {
-    LispGCStats gc_stats;
-    lisp_init();
-    REGISTER_GLOBAL_FUNCTION(cool_func);
-    push_stack_frame(Qnil, Qnil, Qnil);
-    ReadStream s;
-    const char BUF[] = "(cool-func 1 (cons 1 2))";
-    read_stream_init(&s, BUF, sizeof(BUF) - 1);
-    LispVal *l = read(&s);
-    Feval(l);
-    lisp_gc_now(&gc_stats);
-    debug_print_gc_stats(stdout, &gc_stats);
-    pop_stack_frame();
-    lisp_shutdown();
+/* int main(int argc, const cha-r **argv) { */
+/* LispGCStats gc_stats; */
+/* lisp_init(); */
+/* REGISTER_GLOBAL_FUNCTION(cool_func); */
+/* push_stack_frame(Qnil, Qnil, Qnil); */
+/* ReadStream s; */
+/* const char BUF[] = "(cool-func 1 (cons 1 2))"; */
+/* read_stream_init(&s, BUF, sizeof(BUF) - 1); */
+/* LispVal *l = read(&s); */
+/* Feval(l); */
+/* lisp_gc_now(&gc_stats); */
+/* debug_print_gc_stats(stdout, &gc_stats); */
+/* pop_stack_frame(); */
+/* lisp_shutdown(); */
+/*     return 0; */
+/* } */
+
+int main(int argc, const char **argvc) {
     return 0;
 }
diff --git a/src/memory.c b/src/memory.c
index 8698bb3..34ecf88 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -36,3 +36,69 @@ void *lisp_aligned_alloc(size_t alignment, size_t size) {
     }
     return ptr;
 }
+
+#define STRING_STREAM_BLOCK_SIZE 32
+static void ensure_string_stream_space(StringStream *restrict stream,
+                                       size_t space) {
+    size_t min_size = stream->nchars + space;
+    size_t new_size = stream->size;
+    while (new_size < min_size) {
+        new_size += STRING_STREAM_BLOCK_SIZE;
+    }
+    if (new_size != stream->size) {
+        stream->buffer = lisp_realloc(stream->buffer, new_size + 1);
+    }
+}
+
+int string_stream_printf(StringStream *restrict stream,
+                         const char *restrict format, ...) {
+    va_list args;
+    va_start(args, format);
+    int rval = string_stream_vprintf(stream, format, args);
+    va_end(args);
+    return rval;
+}
+
+int string_stream_vprintf(StringStream *restrict stream,
+                          const char *restrict format, va_list args) {
+    va_list args_copy;
+    va_copy(args_copy, args);
+    int space = vsnprintf(NULL, 0, format, args_copy);
+    if (space < 0) {
+        abort();
+    }
+    va_end(args_copy);
+    ensure_string_stream_space(stream, space);
+    int rval = vsnprintf(stream->buffer + stream->nchars,
+                         stream->size + 1 - stream->nchars, format, args);
+    if (rval < 0) {
+        abort();
+    }
+    stream->nchars += rval;
+    return rval;
+}
+
+bool strgetline(const char *restrict buf, size_t buf_length,
+                const char **restrict start, size_t *restrict length) {
+    if (!*start) {
+        *start = buf;
+        if (!buf_length) {
+            *length = 0;
+            return true;
+        }
+    } else if (!buf_length) {
+        return false;
+    } else if (*start + *length >= buf + buf_length - 1) {
+        return false;
+    } else /* if (*start) */ {
+        *start += *length + 1;
+    }
+    size_t left = buf_length - (*start - buf);
+    char *found;
+    if ((found = memchr(*start, '\n', left))) {
+        *length = found - *start;
+    } else {
+        *length = left;
+    }
+    return true;
+}
diff --git a/src/memory.h b/src/memory.h
index 43f504c..fb1e020 100644
--- a/src/memory.h
+++ b/src/memory.h
@@ -2,6 +2,7 @@
 #define INCLUDED_MEMORY_H
 
 #include <float.h>
+#include <stdarg.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -18,6 +19,12 @@
 #    define ALWAYS_INLINE inline
 #endif
 
+#if __has_attribute(format)
+#    define FORMAT(n, m) __attribute__((format(printf, n, m)))
+#else
+#    define FORMAT(n, m)
+#endif
+
 // Byte order stuff
 typedef enum {
     ENDIAN_LITTLE,
@@ -123,4 +130,40 @@ static ALWAYS_INLINE void add_timespecs(const struct timespec *t1,
     out->tv_nsec = nsec;
 }
 
+typedef struct {
+    // this is actually size + 1 bytes for the null byte
+    char *buffer;
+    size_t size;
+    size_t nchars;
+} StringStream;
+
+static inline void string_stream_init(StringStream *restrict stream) {
+    stream->buffer = lisp_malloc(1);
+    stream->size = 0;
+    stream->buffer[stream->size] = '\0';
+    stream->nchars = 0;
+}
+
+static inline void string_stream_free(StringStream *restrict stream) {
+    lisp_free(stream->buffer);
+}
+
+static inline void string_stream_steal(StringStream *restrict stream,
+                                       char **restrict out,
+                                       size_t *restrict out_length) {
+    *out = stream->buffer;
+    *out_length = stream->nchars;
+}
+
+int string_stream_printf(StringStream *restrict stream,
+                         const char *restrict format, ...) FORMAT(2, 3);
+int string_stream_vprintf(StringStream *restrict stream,
+                          const char *restrict format, va_list args);
+
+// Get the next line in BUF starting at *START (or &buf[0] if *START is
+// NULL). Store the length of the line in LENGTH. BUF is BUF_LENGTH bytes
+// long. Return true if we found another line and false otherwise.
+bool strgetline(const char *restrict buf, size_t buf_length,
+                const char **restrict start, size_t *restrict length);
+
 #endif