diff --git a/src/core/asm.c b/src/core/asm.c
index 050aae26..3633360f 100644
--- a/src/core/asm.c
+++ b/src/core/asm.c
@@ -710,8 +710,8 @@ static JanetAssembleResult janet_asm1(JanetAssembler *parent, Janet source, int
             if (!janet_checktype(tup[1], JANET_INTEGER)) {
                 janet_asm_error(&a, "expected integer");
             }
-            mapping.line = janet_unwrap_integer(tup[0]);
-            mapping.column = janet_unwrap_integer(tup[1]);
+            mapping.start = janet_unwrap_integer(tup[0]);
+            mapping.end = janet_unwrap_integer(tup[1]);
             def->sourcemap[i] = mapping;
         }
     }
@@ -876,8 +876,8 @@ Janet janet_disasm(JanetFuncDef *def) {
         for (i = 0; i < def->bytecode_length; i++) {
             Janet *t = janet_tuple_begin(2);
             JanetSourceMapping mapping = def->sourcemap[i];
-            t[0] = janet_wrap_integer(mapping.line);
-            t[1] = janet_wrap_integer(mapping.column);
+            t[0] = janet_wrap_integer(mapping.start);
+            t[1] = janet_wrap_integer(mapping.end);
             sourcemap->data[i] = janet_wrap_tuple(janet_tuple_end(t));
         }
         sourcemap->count = def->bytecode_length;
diff --git a/src/core/bytecode.c b/src/core/bytecode.c
index 83106baf..0112e605 100644
--- a/src/core/bytecode.c
+++ b/src/core/bytecode.c
@@ -125,10 +125,10 @@ int32_t janet_verify(JanetFuncDef *def) {
     for (i = 0; i < def->bytecode_length; i++) {
         uint32_t instr = def->bytecode[i];
         /* Check for invalid instructions */
-        if ((instr & 0xFF) >= JOP_INSTRUCTION_COUNT) {
+        if ((instr & 0x7F) >= JOP_INSTRUCTION_COUNT) {
             return 3;
         }
-        enum JanetInstructionType type = janet_instructions[instr & 0xFF];
+        enum JanetInstructionType type = janet_instructions[instr & 0x7F];
         switch (type) {
             case JINT_0:
                 continue;
diff --git a/src/core/compile.c b/src/core/compile.c
index e67da663..1458347c 100644
--- a/src/core/compile.c
+++ b/src/core/compile.c
@@ -462,9 +462,9 @@ static int macroexpand1(
     if (janet_tuple_length(form) == 0)
         return 0;
     /* Source map - only set when we get a tuple */
-    if (janet_tuple_sm_line(form) > 0) {
-        c->current_mapping.line = janet_tuple_sm_line(form);
-        c->current_mapping.column = janet_tuple_sm_col(form);
+    if (janet_tuple_sm_start(form) >= 0) {
+        c->current_mapping.start = janet_tuple_sm_start(form);
+        c->current_mapping.end = janet_tuple_sm_end(form);
     }
     if (!janet_checktype(form[0], JANET_SYMBOL))
         return 0;
@@ -648,15 +648,15 @@ static void janetc_init(JanetCompiler *c, JanetTable *env, const uint8_t *where)
     c->recursion_guard = JANET_RECURSION_GUARD;
     c->env = env;
     c->source = where;
-    c->current_mapping.line = 0;
-    c->current_mapping.column = 0;
+    c->current_mapping.start = -1;
+    c->current_mapping.end = -1;
     /* Init result */
     c->result.error = NULL;
     c->result.status = JANET_COMPILE_OK;
     c->result.funcdef = NULL;
     c->result.macrofiber = NULL;
-    c->result.error_mapping.line = 0;
-    c->result.error_mapping.column = 0;
+    c->result.error_mapping.start = -1;
+    c->result.error_mapping.end = -1;
 }
 
 /* Deinitialize a compiler struct */
@@ -717,8 +717,8 @@ static int cfun(JanetArgs args) {
     } else {
         t = janet_table(4);
         janet_table_put(t, janet_csymbolv(":error"), janet_wrap_string(res.error));
-        janet_table_put(t, janet_csymbolv(":line"), janet_wrap_integer(res.error_mapping.line));
-        janet_table_put(t, janet_csymbolv(":column"), janet_wrap_integer(res.error_mapping.column));
+        janet_table_put(t, janet_csymbolv(":start"), janet_wrap_integer(res.error_mapping.start));
+        janet_table_put(t, janet_csymbolv(":end"), janet_wrap_integer(res.error_mapping.end));
         if (res.macrofiber) {
             janet_table_put(t, janet_csymbolv(":fiber"), janet_wrap_fiber(res.macrofiber));
         }
diff --git a/src/core/core.janet b/src/core/core.janet
index b2b3a1a0..72ca03f0 100644
--- a/src/core/core.janet
+++ b/src/core/core.janet
@@ -1252,11 +1252,11 @@ value, one key will be ignored."
             (res)
             (do
               (:= good false)
-              (def {:error err :line errl :column errc :fiber errf} res)
+              (def {:error err :start start :end end :fiber errf} res)
               (onstatus
                 :compile
-                (if (< 0 errl)
-                  (string err "\n  in a form at line " errl ", column " errc)
+                (if (<= 0 start)
+                  (string err "\n  at (" start ":" end ")")
                   err)
                 errf
                 where))))
@@ -1309,7 +1309,7 @@ value, one key will be ignored."
               "\n")
   (when f
     (loop
-      [nf :in (reverse (fiber/lineage f))
+      [nf :in (reverse (debug/lineage f))
        :before (file/write stderr "  (fiber)\n")
        {:function func
         :tail tail
@@ -1317,8 +1317,8 @@ value, one key will be ignored."
         :c c
         :name name
         :source source
-        :line source-line
-        :column source-col} :in (fiber/stack nf)]
+        :source-start start
+        :source-end end} :in (debug/stack nf)]
       (file/write stderr "    in")
       (when c (file/write stderr " cfunction"))
       (if name
@@ -1327,14 +1327,15 @@ value, one key will be ignored."
       (if source
         (do
           (file/write stderr " [" source "]")
-          (if source-line
+          (if start
             (file/write
               stderr
-              " on line "
-              (string source-line)
-              ", column "
-              (string source-col)))))
-      (if (and (not source-line) pc)
+              " at ("
+              (string start)
+              ":"
+              (string end)
+              ")"))))
+      (if (and (not start) pc)
         (file/write stderr " (pc=" (string pc) ")"))
       (when tail (file/write stderr " (tailcall)"))
       (file/write stderr "\n"))))
@@ -1507,6 +1508,7 @@ value, one key will be ignored."
   (def newenv (make-env))
   (default chunks (fn [buf _] (file/read stdin :line buf)))
   (default onsignal (fn [sig x f source]
+                      (put newenv '_fiber @{:value f})
                       (case sig
                         :dead (do
                                 (put newenv '_ @{:value x})
diff --git a/src/core/corelib.c b/src/core/corelib.c
index 0190e698..d1282c40 100644
--- a/src/core/corelib.c
+++ b/src/core/corelib.c
@@ -801,6 +801,7 @@ JanetTable *janet_core_env(void) {
         janet_lib_os(args);
         janet_lib_parse(args);
         janet_lib_compile(args);
+        janet_lib_debug(args);
         janet_lib_string(args);
         janet_lib_marsh(args);
 #ifdef JANET_ASSEMBLER
diff --git a/src/core/debug.c b/src/core/debug.c
new file mode 100644
index 00000000..7e9c679f
--- /dev/null
+++ b/src/core/debug.c
@@ -0,0 +1,289 @@
+/*
+* Copyright (c) 2018 Calvin Rose
+*
+* Permission is hereby granted, free of charge, to any person obtaining a copy
+* of this software and associated documentation files (the "Software"), to
+* deal in the Software without restriction, including without limitation the
+* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+* sell copies of the Software, and to permit persons to whom the Software is
+* furnished to do so, subject to the following conditions:
+*
+* The above copyright notice and this permission notice shall be included in
+* all copies or substantial portions of the Software.
+*
+* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+* IN THE SOFTWARE.
+*/
+
+#include <janet/janet.h>
+#include "gc.h"
+#include "state.h"
+
+/* Implements functionality to build a debugger from within janet.
+ * The repl should also be able to serve as pretty featured debugger
+ * out of the box. */
+
+/* Add a break point to a function */
+int janet_debug_break(JanetFuncDef *def, int32_t pc) {
+    if (pc >= def->bytecode_length || pc < 0)
+        return 1;
+    def->bytecode[pc] |= 0x80;
+    return 0;
+}
+
+/* Remove a break point from a function */
+int janet_debug_unbreak(JanetFuncDef *def, int32_t pc) {
+    if (pc >= def->bytecode_length || pc < 0)
+        return 1;
+    def->bytecode[pc] &= ~((uint32_t)0x80);
+    return 0;
+}
+
+/*
+ * Find a location for a breakpoint given a source file an
+ * location.
+ */
+int janet_debug_find(
+        JanetFuncDef **def_out, int32_t *pc_out,
+        const uint8_t *source, int32_t offset) {
+    /* Scan the heap for right func def */
+    JanetGCMemoryHeader *current = janet_vm_blocks;
+    /* Keep track of the best source mapping we have seen so far */
+    int32_t besti = -1;
+    int32_t best_range = INT32_MAX;
+    JanetFuncDef *best_def = NULL;
+    while (NULL != current) {
+        if ((current->flags & JANET_MEM_TYPEBITS) == JANET_MEMORY_FUNCDEF) {
+            JanetFuncDef *def = (JanetFuncDef *)(current + 1);
+            if (def->sourcemap &&
+                    def->source &&
+                    !janet_string_compare(source, def->source)) {
+                /* Correct source file, check mappings. The chosen
+                 * pc index is the first match with the smallest range. */
+                int32_t i;
+                for (i = 0; i < def->bytecode_length; i++) {
+                    int32_t start = def->sourcemap[i].start;
+                    int32_t end = def->sourcemap[i].end;
+                    if (end - start < best_range &&
+                            start <= offset &&
+                            end >= offset) {
+                        best_range = end - start;
+                        besti = i;
+                        best_def = def;
+                    }
+                }
+            }
+        }
+        current = current->next;
+    }
+    if (best_def) {
+        *def_out = best_def;
+        *pc_out = besti;
+        return 0;
+    } else {
+        return 1;
+    }
+}
+
+/*
+ * CFuns
+ */
+
+/* Helper to find funcdef and bytecode offset to insert or remove breakpoints.
+ * Takes a source file name and byte offset. */
+static int helper_find(JanetArgs args, JanetFuncDef **def, int32_t *bytecode_offset) {
+    const uint8_t *source;
+    int32_t source_offset;
+    JANET_FIXARITY(args, 2);
+    JANET_ARG_STRING(source, args, 0);
+    JANET_ARG_INTEGER(source_offset, args, 1);
+    if (janet_debug_find(
+                def, bytecode_offset, source, source_offset)) {
+        JANET_THROW(args, "could not find breakpoint");
+    }
+    JANET_RETURN_NIL(args);
+}
+
+/* Helper to find funcdef and bytecode offset to insert or remove breakpoints.
+ * Takes a function and byte offset*/
+static int helper_find_fun(JanetArgs args, JanetFuncDef **def, int32_t *bytecode_offset) {
+    JanetFunction *func;
+    int32_t offset = 0;
+    JANET_MINARITY(args, 1);
+    JANET_MAXARITY(args, 2);
+    JANET_ARG_FUNCTION(func, args, 0);
+    if (args.n == 2) {
+        JANET_ARG_INTEGER(offset, args, 1);
+    }
+    *def = func->def;
+    *bytecode_offset = offset;
+    JANET_RETURN_NIL(args);
+}
+
+static int cfun_break(JanetArgs args) {
+    JanetFuncDef *def;
+    int32_t offset;
+    int status = helper_find(args, &def, &offset);
+    if (status == 0) janet_debug_break(def, offset);
+    return status;
+}
+
+static int cfun_unbreak(JanetArgs args) {
+    JanetFuncDef *def;
+    int32_t offset;
+    int status = helper_find(args, &def, &offset);
+    if (status == 0) janet_debug_unbreak(def, offset);
+    return status;
+}
+
+static int cfun_fbreak(JanetArgs args) {
+    JanetFuncDef *def;
+    int32_t offset;
+    int status = helper_find_fun(args, &def, &offset);
+    if (status == 0) {
+        if (janet_debug_break(def, offset)) {
+            JANET_THROW(args, "could not find breakpoint");
+        }
+    }
+    return status;
+}
+
+static int cfun_unfbreak(JanetArgs args) {
+    JanetFuncDef *def;
+    int32_t offset;
+    int status = helper_find_fun(args, &def, &offset);
+    if (status == 0) {
+        if (janet_debug_unbreak(def, offset)) {
+            JANET_THROW(args, "could not find breakpoint");
+        }
+    }
+    return status;
+}
+
+static int cfun_lineage(JanetArgs args) {
+    JanetFiber *fiber;
+    JanetArray *array;
+    JANET_FIXARITY(args, 1);
+    JANET_ARG_FIBER(fiber, args, 0);
+    array = janet_array(0);
+    while (fiber) {
+        janet_array_push(array, janet_wrap_fiber(fiber));
+        fiber = fiber->child;
+    }
+    JANET_RETURN_ARRAY(args, array);
+}
+
+/* Extract info from one stack frame */
+static Janet doframe(JanetStackFrame *frame) {
+    int32_t off;
+    JanetTable *t = janet_table(3);
+    JanetFuncDef *def = NULL;
+    if (frame->func) {
+        janet_table_put(t, janet_csymbolv(":function"), janet_wrap_function(frame->func));
+        def = frame->func->def;
+        if (def->name) {
+            janet_table_put(t, janet_csymbolv(":name"), janet_wrap_string(def->name));
+        }
+    } else {
+        JanetCFunction cfun = (JanetCFunction)(frame->pc);
+        if (cfun) {
+            Janet name = janet_table_get(janet_vm_registry, janet_wrap_cfunction(cfun));
+            if (!janet_checktype(name, JANET_NIL)) {
+                janet_table_put(t, janet_csymbolv(":name"), name);
+            }
+        }
+        janet_table_put(t, janet_csymbolv(":c"), janet_wrap_true());
+    }
+    if (frame->flags & JANET_STACKFRAME_TAILCALL) {
+        janet_table_put(t, janet_csymbolv(":tail"), janet_wrap_true());
+    }
+    if (frame->func && frame->pc) {
+        off = (int32_t) (frame->pc - def->bytecode);
+        janet_table_put(t, janet_csymbolv(":pc"), janet_wrap_integer(off));
+        if (def->sourcemap) {
+            JanetSourceMapping mapping = def->sourcemap[off];
+            janet_table_put(t, janet_csymbolv(":source-start"), janet_wrap_integer(mapping.start));
+            janet_table_put(t, janet_csymbolv(":source-end"), janet_wrap_integer(mapping.end));
+        }
+        if (def->source) {
+            janet_table_put(t, janet_csymbolv(":source"), janet_wrap_string(def->source));
+        }
+    }
+    return janet_wrap_table(t);
+}
+
+static int cfun_stack(JanetArgs args) {
+    JanetFiber *fiber;
+    JanetArray *array;
+    JANET_FIXARITY(args, 1);
+    JANET_ARG_FIBER(fiber, args, 0);
+    array = janet_array(0);
+    {
+        int32_t i = fiber->frame;
+        JanetStackFrame *frame;
+        while (i > 0) {
+            frame = (JanetStackFrame *)(fiber->data + i - JANET_FRAME_SIZE);
+            janet_array_push(array, doframe(frame));
+            i = frame->prevframe;
+        }
+    }
+    JANET_RETURN_ARRAY(args, array);
+}
+
+static const JanetReg cfuns[] = {
+    {"debug/break", cfun_break,
+        "(debug/break source byte-offset)\n\n"
+        "Sets a breakpoint with source a key at a given byte offset. An offset "
+        "of 0 is the first byte in a file. Will throw an error if the breakpoint location "
+        "cannot be found. For example\n\n"
+        "\t(debug/break \"core.janet\" 1000)\n\n"
+        "wil set a breakpoint at the 1000th byte of the file core.janet."},
+    {"debug/unbreak", cfun_unbreak,
+        "(debug/unbreak source byte-offset)\n\n"
+        "Remove a breakpoint with a source key at a given byte offset. An offset "
+        "of 0 is the first byte in a file. Will throw an error if the breakpoint "
+        "cannot be found."},
+    {"debug/fbreak", cfun_fbreak,
+        "(debug/fbreak fun [,pc=0])\n\n"
+        "Set a breakpoint in a given function. pc is an optional offset, which "
+        "is in bytecode instructions. fun is a function value. Will throw an error "
+        "if the offset is too large or negative."},
+    {"debug/funbreak", cfun_unfbreak,
+        "(debug/fbreak fun [,pc=0])\n\n"
+        "Unset a breakpoint set with debug/fbreak."},
+    {"debug/stack", cfun_stack,
+        "(debug/stack fib)\n\n"
+        "Gets information about the stack as an array of tables. Each table "
+        "in the array contains information about a stack frame. The top most, current "
+        "stack frame is the first table in the array, and the bottom most stack frame "
+        "is the last value. Each stack frame contains some of the following attributes:\n\n"
+        "\t:c - true if the stack frame is a c function invocation\n"
+        "\t:column - the current source column of the stack frame\n"
+        "\t:function - the function that the stack frame represents\n"
+        "\t:line - the current source line of the stack frame\n"
+        "\t:name - the human friendly name of the function\n"
+        "\t:pc - integer indicating the location of the program counter\n"
+        "\t:source - string with filename or other identifier for the source code\n"
+        "\t:tail - boolean indicating a tail call"
+    },
+    {"debug/lineage", cfun_lineage,
+        "(debug/lineage fib)\n\n"
+        "Returns an array of all child fibers from a root fiber. This function "
+        "is useful when a fiber signals or errors to an ancestor fiber. Using this function, "
+        "the fiber handling the error can see which fiber raised the signal. This function should "
+        "be used mostly for debugging purposes."
+    },
+    {NULL, NULL, NULL}
+};
+
+/* Module entry point */
+int janet_lib_debug(JanetArgs args) {
+    JanetTable *env = janet_env(args);
+    janet_cfuns(env, NULL, cfuns);
+    return 0;
+}
diff --git a/src/core/fiber.c b/src/core/fiber.c
index 7f806c0c..31f9b6e3 100644
--- a/src/core/fiber.c
+++ b/src/core/fiber.c
@@ -349,88 +349,11 @@ static int cfun_new(JanetArgs args) {
 
 static int cfun_status(JanetArgs args) {
     JanetFiber *fiber;
-    const char *status = "";
     JANET_FIXARITY(args, 1);
     JANET_ARG_FIBER(fiber, args, 0);
     uint32_t s = (fiber->flags & JANET_FIBER_STATUS_MASK) >>
         JANET_FIBER_STATUS_OFFSET;
-    switch (s) {
-        case JANET_STATUS_DEAD: status = ":dead"; break;
-        case JANET_STATUS_ERROR: status = ":error"; break;
-        case JANET_STATUS_DEBUG: status = ":debug"; break;
-        case JANET_STATUS_PENDING: status = ":pending"; break;
-        case JANET_STATUS_USER0: status = ":user0"; break;
-        case JANET_STATUS_USER1: status = ":user1"; break;
-        case JANET_STATUS_USER2: status = ":user2"; break;
-        case JANET_STATUS_USER3: status = ":user3"; break;
-        case JANET_STATUS_USER4: status = ":user4"; break;
-        case JANET_STATUS_USER5: status = ":user5"; break;
-        case JANET_STATUS_USER6: status = ":user6"; break;
-        case JANET_STATUS_USER7: status = ":user7"; break;
-        case JANET_STATUS_USER8: status = ":user8"; break;
-        case JANET_STATUS_USER9: status = ":user9"; break;
-        case JANET_STATUS_NEW: status = ":new"; break;
-        default:
-        case JANET_STATUS_ALIVE: status = ":alive"; break;
-    }
-    JANET_RETURN_CSYMBOL(args, status);
-}
-
-/* Extract info from one stack frame */
-static Janet doframe(JanetStackFrame *frame) {
-    int32_t off;
-    JanetTable *t = janet_table(3);
-    JanetFuncDef *def = NULL;
-    if (frame->func) {
-        janet_table_put(t, janet_csymbolv(":function"), janet_wrap_function(frame->func));
-        def = frame->func->def;
-        if (def->name) {
-            janet_table_put(t, janet_csymbolv(":name"), janet_wrap_string(def->name));
-        }
-    } else {
-        JanetCFunction cfun = (JanetCFunction)(frame->pc);
-        if (cfun) {
-            Janet name = janet_table_get(janet_vm_registry, janet_wrap_cfunction(cfun));
-            if (!janet_checktype(name, JANET_NIL)) {
-                janet_table_put(t, janet_csymbolv(":name"), name);
-            }
-        }
-        janet_table_put(t, janet_csymbolv(":c"), janet_wrap_true());
-    }
-    if (frame->flags & JANET_STACKFRAME_TAILCALL) {
-        janet_table_put(t, janet_csymbolv(":tail"), janet_wrap_true());
-    }
-    if (frame->func && frame->pc) {
-        off = (int32_t) (frame->pc - def->bytecode);
-        janet_table_put(t, janet_csymbolv(":pc"), janet_wrap_integer(off));
-        if (def->sourcemap) {
-            JanetSourceMapping mapping = def->sourcemap[off];
-            janet_table_put(t, janet_csymbolv(":line"), janet_wrap_integer(mapping.line));
-            janet_table_put(t, janet_csymbolv(":column"), janet_wrap_integer(mapping.column));
-        }
-        if (def->source) {
-            janet_table_put(t, janet_csymbolv(":source"), janet_wrap_string(def->source));
-        }
-    }
-    return janet_wrap_table(t);
-}
-
-static int cfun_stack(JanetArgs args) {
-    JanetFiber *fiber;
-    JanetArray *array;
-    JANET_FIXARITY(args, 1);
-    JANET_ARG_FIBER(fiber, args, 0);
-    array = janet_array(0);
-    {
-        int32_t i = fiber->frame;
-        JanetStackFrame *frame;
-        while (i > 0) {
-            frame = (JanetStackFrame *)(fiber->data + i - JANET_FRAME_SIZE);
-            janet_array_push(array, doframe(frame));
-            i = frame->prevframe;
-        }
-    }
-    JANET_RETURN_ARRAY(args, array);
+    JANET_RETURN_CSYMBOL(args, janet_status_names[s]);
 }
 
 static int cfun_current(JanetArgs args) {
@@ -438,19 +361,6 @@ static int cfun_current(JanetArgs args) {
     JANET_RETURN_FIBER(args, janet_vm_fiber);
 }
 
-static int cfun_lineage(JanetArgs args) {
-    JanetFiber *fiber;
-    JanetArray *array;
-    JANET_FIXARITY(args, 1);
-    JANET_ARG_FIBER(fiber, args, 0);
-    array = janet_array(0);
-    while (fiber) {
-        janet_array_push(array, janet_wrap_fiber(fiber));
-        fiber = fiber->child;
-    }
-    JANET_RETURN_ARRAY(args, array);
-}
-
 static int cfun_maxstack(JanetArgs args) {
     JanetFiber *fiber;
     JANET_FIXARITY(args, 1);
@@ -500,32 +410,10 @@ static const JanetReg cfuns[] = {
         "\t:alive - the fiber is currently running and cannot be resumed\n"
         "\t:new - the fiber has just been created and not yet run"
     },
-    {"fiber/stack", cfun_stack,
-        "(fiber/stack fib)\n\n"
-        "Gets information about the stack as an array of tables. Each table "
-        "in the array contains information about a stack frame. The top most, current "
-        "stack frame is the first table in the array, and the bottom most stack frame "
-        "is the last value. Each stack frame contains some of the following attributes:\n\n"
-        "\t:c - true if the stack frame is a c function invokation\n"
-        "\t:column - the current source column of the stack frame\n"
-        "\t:function - the function that the stack frame represents\n"
-        "\t:line - the current source line of the stack frame\n"
-        "\t:name - the human friendly name of the function\n"
-        "\t:pc - integer indicating the location of the program counter\n"
-        "\t:source - string with filename or other identifier for the source code\n"
-        "\t:tail - boolean indicating a tail call"
-    },
     {"fiber/current", cfun_current,
         "(fiber/current)\n\n"
         "Returns the currently running fiber."
     },
-    {"fiber/lineage", cfun_lineage,
-        "(fiber/lineage fib)\n\n"
-        "Returns an array of all child fibers from a root fiber. This function "
-        "is useful when a fiber signals or errors to an ancestor fiber. Using this function, "
-        "the fiber handling the error can see which fiber raised the signal. This function should "
-        "be used mostly for debugging purposes."
-    },
     {"fiber/maxstack", cfun_maxstack,
         "(fiber/maxstack fib)\n\n"
         "Gets the maximum stack size in janet values allowed for a fiber. While memory for "
diff --git a/src/core/marsh.c b/src/core/marsh.c
index 4b794e92..53c9103a 100644
--- a/src/core/marsh.c
+++ b/src/core/marsh.c
@@ -234,8 +234,8 @@ static void marshal_one_def(MarshalState *st, JanetFuncDef *def, int flags) {
     if (def->flags & JANET_FUNCDEF_FLAG_HASSOURCEMAP) {
         for (int32_t i = 0; i < def->bytecode_length; i++) {
             JanetSourceMapping map = def->sourcemap[i];
-            pushint(st, map.line);
-            pushint(st, map.column);
+            pushint(st, map.start);
+            pushint(st, map.end);
         }
     }
 }
@@ -740,8 +740,8 @@ static const uint8_t *unmarshal_one_def(
                 JANET_OUT_OF_MEMORY;
             }
             for (int32_t i = 0; i < bytecode_length; i++) {
-                def->sourcemap[i].line = readint(st, &data);
-                def->sourcemap[i].column = readint(st, &data);
+                def->sourcemap[i].start = readint(st, &data);
+                def->sourcemap[i].end = readint(st, &data);
             }
         } else {
             def->sourcemap = NULL;
diff --git a/src/core/parse.c b/src/core/parse.c
index a4845c06..a1cf7d1f 100644
--- a/src/core/parse.c
+++ b/src/core/parse.c
@@ -102,8 +102,7 @@ struct JanetParseState {
     int32_t counter;
     int32_t argn;
     int flags;
-    size_t start_line;
-    size_t start_col;
+    size_t start;
     Consumer consumer;
 };
 
@@ -147,8 +146,7 @@ static void pushstate(JanetParser *p, Consumer consumer, int flags) {
     s.argn = 0;
     s.flags = flags;
     s.consumer = consumer;
-    s.start_line = p->line;
-    s.start_col = p->col;
+    s.start = p->offset;
     _pushstate(p, s);
 }
 
@@ -159,8 +157,8 @@ static void popstate(JanetParser *p, Janet val) {
         if (newtop->flags & PFLAG_CONTAINER) {
             /* Source mapping info */
             if (janet_checktype(val, JANET_TUPLE)) {
-                janet_tuple_sm_line(janet_unwrap_tuple(val)) = (int32_t) top.start_line;
-                janet_tuple_sm_col(janet_unwrap_tuple(val)) = (int32_t) top.start_col;
+                janet_tuple_sm_start(janet_unwrap_tuple(val)) = (int32_t) top.start;
+                janet_tuple_sm_end(janet_unwrap_tuple(val)) = (int32_t) p->offset;
             }
             newtop->argn++;
             push_arg(p, val);
@@ -176,8 +174,8 @@ static void popstate(JanetParser *p, Janet val) {
             t[0] = janet_csymbolv(which);
             t[1] = val;
             /* Quote source mapping info */
-            janet_tuple_sm_line(t) = (int32_t) newtop->start_line;
-            janet_tuple_sm_col(t) = (int32_t) newtop->start_col;
+            janet_tuple_sm_start(t) = (int32_t) newtop->start;
+            janet_tuple_sm_end(t) = (int32_t) p->offset;
             val = janet_wrap_tuple(janet_tuple_end(t));
         } else {
             return;
@@ -522,16 +520,11 @@ static int root(JanetParser *p, JanetParseState *state, uint8_t c) {
 int janet_parser_consume(JanetParser *parser, uint8_t c) {
     int consumed = 0;
     if (parser->error) return 0;
-    if (c == '\n') {
-        parser->line++;
-        parser->col = 0;
-    } else if (c != '\r') {
-        parser->col++;
-    }
     while (!consumed && !parser->error) {
         JanetParseState *state = parser->states + parser->statecount - 1;
         consumed = state->consumer(parser, state, c);
     }
+    parser->offset++;
     parser->lookback = c;
     return 1;
 }
@@ -584,9 +577,8 @@ void janet_parser_init(JanetParser *parser) {
     parser->statecount = 0;
     parser->statecap = 0;
     parser->error = NULL;
-    parser->line = 1;
-    parser->col = 0;
     parser->lookback = -1;
+    parser->offset = 0;
 
     pushstate(parser, root, PFLAG_CONTAINER);
 }
@@ -742,10 +734,7 @@ static int cfun_where(JanetArgs args) {
     JANET_FIXARITY(args, 1);
     JANET_CHECKABSTRACT(args, 0, &janet_parse_parsertype);
     p = (JanetParser *) janet_unwrap_abstract(args.v[0]);
-    Janet *tup = janet_tuple_begin(2);
-    tup[0] = janet_wrap_integer((int32_t)p->line);
-    tup[1] = janet_wrap_integer((int32_t)p->col);
-    JANET_RETURN_TUPLE(args, janet_tuple_end(tup));
+    JANET_RETURN_INTEGER(args, p->offset);
 }
 
 static int cfun_state(JanetArgs args) {
diff --git a/src/core/run.c b/src/core/run.c
index 1d5be862..6a44ab65 100644
--- a/src/core/run.c
+++ b/src/core/run.c
@@ -67,7 +67,7 @@ void janet_stacktrace(JanetFiber *fiber, const char *errtype, Janet err) {
                 int32_t off = (int32_t) (frame->pc - def->bytecode);
                 if (def->sourcemap) {
                     JanetSourceMapping mapping = def->sourcemap[off];
-                    fprintf(stderr, " on line %d, column %d", mapping.line, mapping.column);
+                    fprintf(stderr, " at (%d:%d)", mapping.start, mapping.end);
                 } else {
                     fprintf(stderr, " pc=%d", off);
                 }
@@ -75,6 +75,8 @@ void janet_stacktrace(JanetFiber *fiber, const char *errtype, Janet err) {
             fprintf(stderr, "\n");
         }
     }
+
+    janet_v_free(fibers);
 }
 
 /* Run a string */
diff --git a/src/core/tuple.c b/src/core/tuple.c
index c8f3dd65..b64a9b52 100644
--- a/src/core/tuple.c
+++ b/src/core/tuple.c
@@ -32,8 +32,8 @@ Janet *janet_tuple_begin(int32_t length) {
     char *data = janet_gcalloc(JANET_MEMORY_TUPLE, 4 * sizeof(int32_t) + length * sizeof(Janet));
     Janet *tuple = (Janet *)(data + (4 * sizeof(int32_t)));
     janet_tuple_length(tuple) = length;
-    janet_tuple_sm_line(tuple) = 0;
-    janet_tuple_sm_col(tuple) = 0;
+    janet_tuple_sm_start(tuple) = -1;
+    janet_tuple_sm_end(tuple) = -1;
     return tuple;
 }
 
diff --git a/src/core/util.c b/src/core/util.c
index 27450911..200e381f 100644
--- a/src/core/util.c
+++ b/src/core/util.c
@@ -53,6 +53,42 @@ const char *const janet_type_names[16] = {
     ":abstract"
 };
 
+const char *const janet_signal_names[14] = {
+    ":ok",
+    ":error",
+    ":debug",
+    ":yield",
+    ":user0",
+    ":user1",
+    ":user2",
+    ":user3",
+    ":user4",
+    ":user5",
+    ":user6",
+    ":user7",
+    ":user8",
+    ":user9"
+};
+
+const char *const janet_status_names[16] = {
+    ":dead",
+    ":error",
+    ":debug",
+    ":pending",
+    ":user0",
+    ":user1",
+    ":user2",
+    ":user3",
+    ":user4",
+    ":user5",
+    ":user6",
+    ":user7",
+    ":user8",
+    ":user9",
+    ":new",
+    ":alive"
+};
+
 /* Calculate hash for string */
 
 int32_t janet_string_calchash(const uint8_t *str, int32_t len) {
diff --git a/src/core/util.h b/src/core/util.h
index 4b1cecfb..1bc7cc4d 100644
--- a/src/core/util.h
+++ b/src/core/util.h
@@ -57,5 +57,6 @@ int janet_lib_parse(JanetArgs args);
 int janet_lib_asm(JanetArgs args);
 #endif
 int janet_lib_compile(JanetArgs args);
+int janet_lib_debug(JanetArgs args);
 
 #endif
diff --git a/src/core/vm.c b/src/core/vm.c
index 09a1b6f3..1e1d2453 100644
--- a/src/core/vm.c
+++ b/src/core/vm.c
@@ -54,6 +54,8 @@ JanetSignal janet_continue(JanetFiber *fiber, Janet in, Janet *out) {
     /* Expected types on type error */
     uint16_t expected_types;
 
+    uint8_t first_opcode;
+
     /* Signal to return when done */
     JanetSignal signal = JANET_SIGNAL_OK;
 
@@ -92,16 +94,24 @@ JanetSignal janet_continue(JanetFiber *fiber, Janet in, Janet *out) {
          * instruction. */
         retreg = in;
         goto vm_resume_child;
-    } else if (startstatus != JANET_STATUS_NEW) {
+    } else if (startstatus != JANET_STATUS_NEW && 
+            ((*pc & 0xFF) == JOP_SIGNAL)) {
         /* Only should be hit if child is waiting on a SIGNAL instruction */
         /* If waiting for response to signal, use input and increment pc */
         stack[oparg(1, 0xFF)] = in;
         pc++;
     }
 
+    /* The first opcode to execute. If the first opcode has
+     * the breakpoint bit set and we were in the debug state, skip
+     * that first breakpoint. */
+    first_opcode = (startstatus == JANET_STATUS_DEBUG)
+        ? (*pc & 0x7F)
+        : (*pc & 0xFF);
+
 /* Use computed gotos for GCC and clang, otherwise use switch */
-#ifdef __GNUC__
-#define VM_START() {vm_next();
+#ifdef ____GNUC__
+#define VM_START() { goto *op_lookup[first_opcode];
 #define VM_END() }
 #define VM_OP(op) label_##op :
 #define VM_DEFAULT() label_unknown_op:
@@ -193,11 +203,11 @@ static void *op_lookup[255] = {
     &&label_unknown_op
 };
 #else
-#define VM_START() for(;;){switch(*pc & 0xFF){
+#define VM_START() uint8_t opcode = first_opcode; for (;;) {switch(opcode) {
 #define VM_END() }}
 #define VM_OP(op) case op :
 #define VM_DEFAULT() default:
-#define vm_next() continue
+#define vm_next() opcode = *pc & 0xFF; continue
 #endif
 
 #define vm_checkgc_next() janet_maybe_collect(); vm_next()
@@ -279,6 +289,7 @@ static void *op_lookup[255] = {
     VM_START();
 
     VM_DEFAULT();
+    signal = JANET_SIGNAL_DEBUG;
     retreg = janet_wrap_nil();
     goto vm_exit;
 
@@ -535,7 +546,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_GREATER_THAN_INTEGER)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_integer(stack[oparg(2, 0xFF)]) >
@@ -543,7 +553,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_GREATER_THAN_IMMEDIATE)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_integer(stack[oparg(2, 0xFF)]) > ((*(int32_t *)pc) >> 24)
@@ -551,7 +560,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_GREATER_THAN_REAL)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_real(stack[oparg(2, 0xFF)]) >
@@ -559,7 +567,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_GREATER_THAN_EQUAL_REAL)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_real(stack[oparg(2, 0xFF)]) >=
@@ -575,7 +582,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_EQUALS_INTEGER)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_integer(stack[oparg(2, 0xFF)]) ==
@@ -584,7 +590,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_EQUALS_REAL)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_real(stack[oparg(2, 0xFF)]) ==
@@ -593,7 +598,6 @@ static void *op_lookup[255] = {
     pc++;
     vm_next();
 
-    /* Candidate */
     VM_OP(JOP_EQUALS_IMMEDIATE)
     stack[oparg(1, 0xFF)] = janet_wrap_boolean(
             janet_unwrap_integer(stack[oparg(2, 0xFF)]) == ((*(int32_t *)pc) >> 24)
diff --git a/src/include/janet/janet.h b/src/include/janet/janet.h
index ec5bcf1d..2543441b 100644
--- a/src/include/janet/janet.h
+++ b/src/include/janet/janet.h
@@ -204,6 +204,8 @@ extern "C" {
 
 /* Names of all of the types */
 extern const char *const janet_type_names[16];
+extern const char *const janet_signal_names[14];
+extern const char *const janet_status_names[16];
 
 /* Fiber signals */
 typedef enum {
@@ -667,8 +669,8 @@ struct JanetKV {
 
 /* Source mapping structure for a bytecode instruction */
 struct JanetSourceMapping {
-    int32_t line;
-    int32_t column;
+    int32_t start;
+    int32_t end;
 };
 
 /* A function definition. Contains information needed to instantiate closures. */
@@ -731,8 +733,7 @@ struct JanetParser {
     size_t statecap;
     size_t bufcount;
     size_t bufcap;
-    size_t line;
-    size_t col;
+    size_t offset;
     int lookback;
 };
 
@@ -967,8 +968,8 @@ JANET_API int janet_buffer_push_u64(JanetBuffer *buffer, uint64_t x);
 #define janet_tuple_raw(t) ((int32_t *)(t) - 4)
 #define janet_tuple_length(t) (janet_tuple_raw(t)[0])
 #define janet_tuple_hash(t) ((janet_tuple_raw(t)[1]))
-#define janet_tuple_sm_line(t) ((janet_tuple_raw(t)[2]))
-#define janet_tuple_sm_col(t) ((janet_tuple_raw(t)[3]))
+#define janet_tuple_sm_start(t) ((janet_tuple_raw(t)[2]))
+#define janet_tuple_sm_end(t) ((janet_tuple_raw(t)[3]))
 JANET_API Janet *janet_tuple_begin(int32_t length);
 JANET_API const Janet *janet_tuple_end(Janet *tuple);
 JANET_API const Janet *janet_tuple_n(const Janet *values, int32_t n);
diff --git a/src/mainclient/init.janet b/src/mainclient/init.janet
index d82d10fd..5ac289eb 100644
--- a/src/mainclient/init.janet
+++ b/src/mainclient/init.janet
@@ -55,6 +55,6 @@
       (do
         (print (string "Janet " janet/version "-" janet/build "  Copyright (C) 2017-2018 Calvin Rose"))
         (repl (fn [buf p]
-                (def [line] (parser/where p))
-                (def prompt (string "janet:" line ":" (parser/state p) "> "))
+                (def offset (parser/where p))
+                (def prompt (string "janet:" offset ":" (parser/state p) "> "))
                 (getline prompt buf)))))))