diff --git a/CHANGELOG.md b/CHANGELOG.md
index afc08f82..b21671d0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,13 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased
+- Add `math/rng`, `math/rng-int`, and `math/rng-uniform`.
+- Add `in` function to index in a stricter manner. Opposingly, `get` will
+  now not throw errors on bad keys.
+- Indexed types and byte sequences will now error when indexed out of range or
+  with bad keys.
+- Add rng functions to Janet. This also replaces the RNG behind `math/random`
+  and `math/seedrandom` with a consistent, platform independent RNG.
 - Add `with-vars` macro.
 - Add the `quickbin` command to jpm.
 - Create shell.c when making the amlagamated source. This can be compiled with
diff --git a/src/boot/boot.janet b/src/boot/boot.janet
index dcb29ad2..4532a6d1 100644
--- a/src/boot/boot.janet
+++ b/src/boot/boot.janet
@@ -25,14 +25,14 @@
               (array/push modifiers ith))
             (if (< i len) (recur (+ i 1)))))))
     (def start (fstart 0))
-    (def args (get more start))
+    (def args (in more start))
     # Add function signature to docstring
     (var index 0)
     (def arglen (length args))
     (def buf (buffer "(" name))
     (while (< index arglen)
       (buffer/push-string buf " ")
-      (buffer/format buf "%p" (get args index))
+      (buffer/format buf "%p" (in args index))
       (set index (+ index 1)))
     (array/push modifiers (string buf ")\n\n" docstr))
     # Build return value
@@ -116,7 +116,7 @@
        :table true
        :buffer true
        :struct true})
-    (fn idempotent? [x] (not (get non-atomic-types (type x))))))
+    (fn idempotent? [x] (not (in non-atomic-types (type x))))))
 
 # C style macros and functions for imperative sugar. No bitwise though.
 (defn inc "Returns x + 1." [x] (+ x 1))
@@ -163,9 +163,9 @@
   (defn aux [i]
     (def restlen (- (length pairs) i))
     (if (= restlen 0) nil
-      (if (= restlen 1) (get pairs i)
-        (tuple 'if (get pairs i)
-               (get pairs (+ i 1))
+      (if (= restlen 1) (in pairs i)
+        (tuple 'if (in pairs i)
+               (in pairs (+ i 1))
                (aux (+ i 2))))))
   (aux 0))
 
@@ -179,9 +179,9 @@
   (defn aux [i]
     (def restlen (- (length pairs) i))
     (if (= restlen 0) nil
-      (if (= restlen 1) (get pairs i)
-        (tuple 'if (tuple = sym (get pairs i))
-               (get pairs (+ i 1))
+      (if (= restlen 1) (in pairs i)
+        (tuple 'if (tuple = sym (in pairs i))
+               (in pairs (+ i 1))
                (aux (+ i 2))))))
   (if atm
     (aux 0)
@@ -231,8 +231,8 @@
   (while (> i 0)
     (-- i)
     (set ret (if (= ret true)
-               (get forms i)
-               (tuple 'if (get forms i) ret))))
+               (in forms i)
+               (tuple 'if (in forms i) ret))))
   ret)
 
 (defmacro or
@@ -244,7 +244,7 @@
   (var i len)
   (while (> i 0)
     (-- i)
-    (def fi (get forms i))
+    (def fi (in forms i))
     (set ret (if (idempotent? fi)
                (tuple 'if fi fi ret)
                (do
@@ -260,7 +260,7 @@
   (def len (length syms))
   (def accum @[])
   (while (< i len)
-    (array/push accum (get syms i) [gensym])
+    (array/push accum (in syms i) [gensym])
     (++ i))
   ~(let (,;accum) ,;body))
 
@@ -299,7 +299,7 @@
        ,(unless (= ds in) ~(def ,ds ,in))
        (def ,len (,length ,ds))
        (while (,< ,i ,len)
-         (def ,binding (get ,ds ,i))
+         (def ,binding (in ,ds ,i))
          ,;body
          (++ ,i)))))
 
@@ -311,7 +311,7 @@
        ,(unless (= ds in) ~(def ,ds ,in))
        (var ,k (,next ,ds nil))
        (while ,k
-         (def ,binding ,(if pair? ~(tuple ,k (get ,ds ,k)) k))
+         (def ,binding ,(if pair? ~(tuple ,k (in ,ds ,k)) k))
          ,;body
          (set ,k (,next ,ds ,k))))))
 
@@ -327,48 +327,47 @@
 (defn- loop1
   [body head i]
 
+  # Terminate recursion
+  (when (<= (length head) i)
+    (break ~(do ,;body)))
+
   (def {i binding
-        (+ i 1) verb
-        (+ i 2) object} head)
+        (+ i 1) verb} head)
 
-  (cond
+  # 2 term expression
+  (when (keyword? binding)
+    (break
+      (let [rest (loop1 body head (+ i 2))]
+        (case binding
+          :until ~(do (if ,verb (break) nil) ,rest)
+          :while ~(do (if ,verb nil (break)) ,rest)
+          :let ~(let ,verb (do ,rest))
+          :after ~(do ,rest ,verb nil)
+          :before ~(do ,verb ,rest nil)
+          :repeat (with-syms [iter]
+                    ~(do (var ,iter ,verb) (while (> ,iter 0) ,rest (-- ,iter))))
+          :when ~(when ,verb ,rest)
+          (error (string "unexpected loop modifier " binding))))))
 
-    # Terminate recursion
-    (<= (length head) i)
-    ~(do ,;body)
-
-    # 2 term expression
-    (keyword? binding)
-    (let [rest (loop1 body head (+ i 2))]
-      (case binding
-        :until ~(do (if ,verb (break) nil) ,rest)
-        :while ~(do (if ,verb nil (break)) ,rest)
-        :let ~(let ,verb (do ,rest))
-        :after ~(do ,rest ,verb nil)
-        :before ~(do ,verb ,rest nil)
-        :repeat (with-syms [iter]
-                  ~(do (var ,iter ,verb) (while (> ,iter 0) ,rest (-- ,iter))))
-        :when ~(when ,verb ,rest)
-        (error (string "unexpected loop modifier " binding))))
-
-    # 3 term expression
-    (let [rest (loop1 body head (+ i 3))]
-      (case verb
-        :range (let [[start stop step] object]
-                 (for-template binding start stop (or step 1) < + [rest]))
-        :keys (keys-template binding object false [rest])
-        :pairs (keys-template binding object true [rest])
-        :down (let [[start stop step] object]
-                (for-template binding start stop (or step 1) > - [rest]))
-        :in (each-template binding object [rest])
-        :iterate (iterate-template binding object rest)
-        :generate (with-syms [f s]
-                    ~(let [,f ,object]
-                       (while true
-                         (def ,binding (,resume ,f))
-                         (if (= :dead (,fiber/status ,f)) (break))
-                         ,rest)))
-        (error (string "unexpected loop verb " verb))))))
+  # 3 term expression
+  (def {(+ i 2) object} head)
+  (let [rest (loop1 body head (+ i 3))]
+    (case verb
+      :range (let [[start stop step] object]
+               (for-template binding start stop (or step 1) < + [rest]))
+      :keys (keys-template binding object false [rest])
+      :pairs (keys-template binding object true [rest])
+      :down (let [[start stop step] object]
+              (for-template binding start stop (or step 1) > - [rest]))
+      :in (each-template binding object [rest])
+      :iterate (iterate-template binding object rest)
+      :generate (with-syms [f s]
+                  ~(let [,f ,object]
+                     (while true
+                       (def ,binding (,resume ,f))
+                       (if (= :dead (,fiber/status ,f)) (break))
+                       ,rest)))
+      (error (string "unexpected loop verb " verb)))))
 
 (defmacro for
   "Do a c style for loop for side effects. Returns nil."
@@ -466,11 +465,11 @@
   (if (zero? len) (error "expected at least 1 binding"))
   (if (odd? len) (error "expected an even number of bindings"))
   (defn aux [i]
-    (def bl (get bindings i))
-    (def br (get bindings (+ 1 i)))
     (if (>= i len)
       tru
       (do
+        (def bl (in bindings i))
+        (def br (in bindings (+ 1 i)))
         (def atm (idempotent? bl))
         (def sym (if atm bl (gensym)))
         (if atm
@@ -499,7 +498,7 @@
   [& functions]
   (case (length functions)
     0 nil
-    1 (get functions 0)
+    1 (in functions 0)
     2 (let [[f g]       functions] (fn [& x] (f (g ;x))))
     3 (let [[f g h]     functions] (fn [& x] (f (g (h ;x)))))
     4 (let [[f g h i]   functions] (fn [& x] (f (g (h (i ;x))))))
@@ -547,12 +546,12 @@
 (defn first
   "Get the first element from an indexed data structure."
   [xs]
-  (get xs 0))
+  (in xs 0))
 
 (defn last
   "Get the last element from an indexed data structure."
   [xs]
-  (get xs (- (length xs) 1)))
+  (in xs (- (length xs) 1)))
 
 ###
 ###
@@ -566,16 +565,16 @@
 
     (defn part
       [a lo hi by]
-      (def pivot (get a hi))
+      (def pivot (in a hi))
       (var i lo)
       (for j lo hi
-        (def aj (get a j))
+        (def aj (in a j))
         (when (by aj pivot)
-          (def ai (get a i))
+          (def ai (in a i))
           (set (a i) aj)
           (set (a j) ai)
           (++ i)))
-      (set (a hi) (get a i))
+      (set (a hi) (in a i))
       (set (a i) pivot)
       i)
 
@@ -609,20 +608,20 @@
   [f & inds]
   (def ninds (length inds))
   (if (= 0 ninds) (error "expected at least 1 indexed collection"))
-  (var limit (length (get inds 0)))
+  (var limit (length (in inds 0)))
   (for i 0 ninds
-    (def l (length (get inds i)))
+    (def l (length (in inds i)))
     (if (< l limit) (set limit l)))
   (def [i1 i2 i3 i4] inds)
   (def res (array/new limit))
   (case ninds
-    1 (for i 0 limit (set (res i) (f (get i1 i))))
-    2 (for i 0 limit (set (res i) (f (get i1 i) (get i2 i))))
-    3 (for i 0 limit (set (res i) (f (get i1 i) (get i2 i) (get i3 i))))
-    4 (for i 0 limit (set (res i) (f (get i1 i) (get i2 i) (get i3 i) (get i4 i))))
+    1 (for i 0 limit (set (res i) (f (in i1 i))))
+    2 (for i 0 limit (set (res i) (f (in i1 i) (in i2 i))))
+    3 (for i 0 limit (set (res i) (f (in i1 i) (in i2 i) (in i3 i))))
+    4 (for i 0 limit (set (res i) (f (in i1 i) (in i2 i) (in i3 i) (in i4 i))))
     (for i 0 limit
       (def args (array/new ninds))
-      (for j 0 ninds (set (args j) (get (get inds j) i)))
+      (for j 0 ninds (set (args j) (in (in inds j) i)))
       (set (res i) (f ;args))))
   res)
 
@@ -695,7 +694,7 @@
   (var i 0)
   (var going true)
   (while (if (< i len) going)
-    (def item (get ind i))
+    (def item (in ind i))
     (if (pred item) (set going false) (++ i)))
   (if going nil i))
 
@@ -705,7 +704,7 @@
   and a not found. Consider find-index if this is an issue."
   [pred ind]
   (def i (find-index pred ind))
-  (if (= i nil) nil (get ind i)))
+  (if (= i nil) nil (in ind i)))
 
 (defn take
   "Take first n elements in an indexed type. Returns new indexed instance."
@@ -783,7 +782,7 @@
   [x & forms]
   (defn fop [last n]
     (def [h t] (if (= :tuple (type n))
-                 (tuple (get n 0) (array/slice n 1))
+                 (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def parts (array/concat @[h last] t))
     (tuple/slice parts 0))
@@ -796,7 +795,7 @@
   [x & forms]
   (defn fop [last n]
     (def [h t] (if (= :tuple (type n))
-                 (tuple (get n 0) (array/slice n 1))
+                 (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def parts (array/concat @[h] t @[last]))
     (tuple/slice parts 0))
@@ -811,7 +810,7 @@
   [x & forms]
   (defn fop [last n]
     (def [h t] (if (= :tuple (type n))
-                 (tuple (get n 0) (array/slice n 1))
+                 (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def sym (gensym))
     (def parts (array/concat @[h sym] t))
@@ -827,7 +826,7 @@
   [x & forms]
   (defn fop [last n]
     (def [h t] (if (= :tuple (type n))
-                 (tuple (get n 0) (array/slice n 1))
+                 (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def sym (gensym))
     (def parts (array/concat @[h] t @[sym]))
@@ -843,7 +842,7 @@
 (defn walk-dict [f form]
   (def ret @{})
   (loop [k :keys form]
-    (put ret (f k) (f (get form k))))
+    (put ret (f k) (f (in form k))))
   ret)
 
 (defn walk
@@ -950,7 +949,7 @@
   (var n (- len 1))
   (def reversed (array/new len))
   (while (>= n 0)
-    (array/push reversed (get t n))
+    (array/push reversed (in t n))
     (-- n))
   reversed)
 
@@ -961,7 +960,7 @@
   [ds]
   (def ret @{})
   (loop [k :keys ds]
-    (put ret (get ds k) k))
+    (put ret (in ds k) k))
   ret)
 
 (defn zipcoll
@@ -973,7 +972,7 @@
   (def lv (length vals))
   (def len (if (< lk lv) lk lv))
   (for i 0 len
-    (put res (get keys i) (get vals i)))
+    (put res (in keys i) (in vals i)))
   res)
 
 (defn get-in
@@ -1043,7 +1042,7 @@
   [tab & colls]
   (loop [c :in colls
          key :keys c]
-    (set (tab key) (get c key)))
+    (set (tab key) (in c key)))
   tab)
 
 (defn merge
@@ -1054,7 +1053,7 @@
   (def container @{})
   (loop [c :in colls
          key :keys c]
-    (set (container key) (get c key)))
+    (set (container key) (in c key)))
   container)
 
 (defn keys
@@ -1073,7 +1072,7 @@
   (def arr (array/new (length x)))
   (var k (next x nil))
   (while (not= nil k)
-    (array/push arr (get x k))
+    (array/push arr (in x k))
     (set k (next x k)))
   arr)
 
@@ -1083,7 +1082,7 @@
   (def arr (array/new (length x)))
   (var k (next x nil))
   (while (not= nil k)
-    (array/push arr (tuple k (get x k)))
+    (array/push arr (tuple k (in x k)))
     (set k (next x k)))
   arr)
 
@@ -1092,7 +1091,7 @@
   [ind]
   (def freqs @{})
   (each x ind
-    (def n (get freqs x))
+    (def n (in freqs x))
     (set (freqs x) (if n (+ 1 n) 1)))
   freqs)
 
@@ -1106,7 +1105,7 @@
     (def len (min ;(map length cols)))
     (loop [i :range [0 len]
            ci :range [0 ncol]]
-      (array/push res (get (get cols ci) i))))
+      (array/push res (in (in cols ci) i))))
   res)
 
 (defn distinct
@@ -1114,7 +1113,7 @@
   [xs]
   (def ret @[])
   (def seen @{})
-  (each x xs (if (get seen x) nil (do (put seen x true) (array/push ret x))))
+  (each x xs (if (in seen x) nil (do (put seen x true) (array/push ret x))))
   ret)
 
 (defn flatten-into
@@ -1138,7 +1137,7 @@
   like @[k v k v ...]. Returns a new array."
   [dict]
   (def ret (array/new (* 2 (length dict))))
-  (loop [k :keys dict] (array/push ret k (get dict k)))
+  (loop [k :keys dict] (array/push ret k (in dict k)))
   ret)
 
 (defn interpose
@@ -1147,10 +1146,10 @@
   [sep ind]
   (def len (length ind))
   (def ret (array/new (- (* 2 len) 1)))
-  (if (> len 0) (put ret 0 (get ind 0)))
+  (if (> len 0) (put ret 0 (in ind 0)))
   (var i 1)
   (while (< i len)
-    (array/push ret sep (get ind i))
+    (array/push ret sep (in ind i))
     (++ i))
   ret)
 
@@ -1233,7 +1232,7 @@
   (cond
 
     (symbol? pattern)
-    (if (get seen pattern)
+    (if (in seen pattern)
       ~(if (= ,pattern ,expr) ,(onmatch) ,sentinel)
       (do
         (put seen pattern true)
@@ -1244,7 +1243,7 @@
       # Unification with external values
       ~(if (= ,(pattern 1) ,expr) ,(onmatch) ,sentinel)
       (match-1
-        (get pattern 0) expr
+        (in pattern 0) expr
         (fn []
           ~(if (and ,;(tuple/slice pattern 1)) ,(onmatch) ,sentinel)) seen))
 
@@ -1259,7 +1258,7 @@
                (++ i)
                (if (= i len)
                  (onmatch)
-                 (match-1 (get pattern i) (tuple get $arr i) aux seen))))
+                 (match-1 (in pattern i) (tuple in $arr i) aux seen))))
            ,sentinel)))
 
     (dictionary? pattern)
@@ -1272,7 +1271,7 @@
                (set key (next pattern key))
                (if (= key nil)
                  (onmatch)
-                 (match-1 (get pattern key) (tuple get $dict key) aux seen))))
+                 (match-1 (in pattern key) (tuple in $dict key) aux seen))))
            ,sentinel)))
 
     :else ~(if (= ,pattern ,expr) ,(onmatch) ,sentinel)))
@@ -1293,9 +1292,9 @@
     (def len-1 (dec len))
     ((fn aux [i]
        (cond
-         (= i len-1) (get cases i)
+         (= i len-1) (in cases i)
          (< i len-1) (with-syms [$res]
-                       ~(if (= ,sentinel (def ,$res ,(match-1 (get cases i) $x (fn [] (get cases (inc i))) @{})))
+                       ~(if (= ,sentinel (def ,$res ,(match-1 (in cases i) $x (fn [] (in cases (inc i))) @{})))
                           ,(aux (+ 2 i))
                           ,$res)))) 0)))
 
@@ -1357,7 +1356,7 @@
       (def bind-type
         (string "    "
                 (cond
-                  (x :ref) (string :var " (" (type (get (x :ref) 0)) ")")
+                  (x :ref) (string :var " (" (type (in (x :ref) 0)) ")")
                   (x :macro) :macro
                   (type (x :value)))
                 "\n"))
@@ -1397,7 +1396,7 @@
     (def newt @{})
     (var key (next t nil))
     (while (not= nil key)
-      (put newt (recur key) (on-value (get t key)))
+      (put newt (recur key) (on-value (in t key)))
       (set key (next t key)))
     newt)
 
@@ -1410,24 +1409,24 @@
       (recur x)))
 
   (defn expanddef [t]
-    (def last (get t (- (length t) 1)))
-    (def bound (get t 1))
+    (def last (in t (- (length t) 1)))
+    (def bound (in t 1))
     (tuple/slice
       (array/concat
-        @[(get t 0) (expand-bindings bound)]
+        @[(in t 0) (expand-bindings bound)]
         (tuple/slice t 2 -2)
         @[(recur last)])))
 
   (defn expandall [t]
     (def args (map recur (tuple/slice t 1)))
-    (tuple (get t 0) ;args))
+    (tuple (in t 0) ;args))
 
   (defn expandfn [t]
-    (def t1 (get t 1))
+    (def t1 (in t 1))
     (if (symbol? t1)
       (do
         (def args (map recur (tuple/slice t 3)))
-        (tuple 'fn t1 (get t 2) ;args))
+        (tuple 'fn t1 (in t 2) ;args))
       (do
         (def args (map recur (tuple/slice t 2)))
         (tuple 'fn t1 ;args))))
@@ -1436,15 +1435,15 @@
     (defn qq [x]
       (case (type x)
         :tuple (do
-                 (def x0 (get x 0))
+                 (def x0 (in x 0))
                  (if (or (= 'unquote x0) (= 'unquote-splicing x0))
-                   (tuple x0 (recur (get x 1)))
+                   (tuple x0 (recur (in x 1)))
                    (tuple/slice (map qq x))))
         :array (map qq x)
         :table (table (map qq (kvs x)))
         :struct (struct (map qq (kvs x)))
         x))
-    (tuple (get t 0) (qq (get t 1))))
+    (tuple (in t 0) (qq (in t 1))))
 
   (def specs
     {'set expanddef
@@ -1458,8 +1457,8 @@
      'while expandall})
 
   (defn dotup [t]
-    (def h (get t 0))
-    (def s (get specs h))
+    (def h (in t 0))
+    (def s (in specs h))
     (def entry (or (dyn h) {}))
     (def m (entry :value))
     (def m? (entry :macro))
@@ -1956,7 +1955,7 @@
   [path & args]
   (def [fullpath mod-kind] (module/find path))
   (unless fullpath (error mod-kind))
-  (if-let [check (get module/cache fullpath)]
+  (if-let [check (in module/cache fullpath)]
     check
     (do
       (def loader (module/loaders mod-kind))
@@ -2123,25 +2122,25 @@ _fiber is bound to the suspended fiber
      "q" (fn [&] (set *quiet* true) 1)
      "k" (fn [&] (set *compile-only* true) (set *exit-on-error* false) 1)
      "n" (fn [&] (set *colorize* false) 1)
-     "m" (fn [i &] (setdyn :syspath (get args (+ i 1))) 2)
+     "m" (fn [i &] (setdyn :syspath (in args (+ i 1))) 2)
      "c" (fn [i &]
-           (def e (dofile (get args (+ i 1))))
-           (spit (get args (+ i 2)) (make-image e))
+           (def e (dofile (in args (+ i 1))))
+           (spit (in args (+ i 2)) (make-image e))
            (set *no-file* false)
            3)
      "-" (fn [&] (set *handleopts* false) 1)
      "l" (fn [i &]
-           (import* (get args (+ i 1))
+           (import* (in args (+ i 1))
                     :prefix "" :exit *exit-on-error*)
            2)
      "e" (fn [i &]
            (set *no-file* false)
-           (eval-string (get args (+ i 1)))
+           (eval-string (in args (+ i 1)))
            2)})
 
   (defn- dohandler [n i &]
-    (def h (get handlers n))
-    (if h (h i) (do (print "unknown flag -" n) ((get handlers "h")))))
+    (def h (in handlers n))
+    (if h (h i) (do (print "unknown flag -" n) ((in handlers "h")))))
 
   (def- safe-forms {'defn true 'defn- true 'defmacro true 'defmacro- true})
   (def- importers {'import true 'import* true 'use true 'dofile true 'require true})
@@ -2162,7 +2161,7 @@ _fiber is bound to the suspended fiber
   (var i 0)
   (def lenargs (length args))
   (while (< i lenargs)
-    (def arg (get args i))
+    (def arg (in args i))
     (if (and *handleopts* (= "-" (string/slice arg 0 1)))
       (+= i (dohandler (string/slice arg 1 2) i))
       (do
diff --git a/src/core/capi.c b/src/core/capi.c
index d4548e22..6cb81712 100644
--- a/src/core/capi.c
+++ b/src/core/capi.c
@@ -129,7 +129,7 @@ const char *janet_getcstring(const Janet *argv, int32_t n) {
 int32_t janet_getinteger(const Janet *argv, int32_t n) {
     Janet x = argv[n];
     if (!janet_checkint(x)) {
-        janet_panicf("bad slot #%d, expected integer, got %v", n, x);
+        janet_panicf("bad slot #%d, expected 32 bit signed integer, got %v", n, x);
     }
     return janet_unwrap_integer(x);
 }
@@ -137,7 +137,7 @@ int32_t janet_getinteger(const Janet *argv, int32_t n) {
 int64_t janet_getinteger64(const Janet *argv, int32_t n) {
     Janet x = argv[n];
     if (!janet_checkint64(x)) {
-        janet_panicf("bad slot #%d, expected 64 bit integer, got %v", n, x);
+        janet_panicf("bad slot #%d, expected 64 bit signed integer, got %v", n, x);
     }
     return (int64_t) janet_unwrap_number(x);
 }
diff --git a/src/core/cfuns.c b/src/core/cfuns.c
index e5d6755c..49ddf320 100644
--- a/src/core/cfuns.c
+++ b/src/core/cfuns.c
@@ -104,7 +104,7 @@ static JanetSlot do_debug(JanetFopts opts, JanetSlot *args) {
     janetc_emit(opts.compiler, JOP_SIGNAL | (2 << 24));
     return janetc_cslot(janet_wrap_nil());
 }
-static JanetSlot do_get(JanetFopts opts, JanetSlot *args) {
+static JanetSlot do_in(JanetFopts opts, JanetSlot *args) {
     return opreduce(opts, args, JOP_GET, janet_wrap_nil());
 }
 static JanetSlot do_put(JanetFopts opts, JanetSlot *args) {
@@ -275,7 +275,7 @@ static const JanetFunOptimizer optimizers[] = {
     {minarity2, do_apply},
     {maxarity1, do_yield},
     {fixarity2, do_resume},
-    {fixarity2, do_get},
+    {fixarity2, do_in},
     {fixarity3, do_put},
     {fixarity1, do_length},
     {NULL, do_add},
diff --git a/src/core/compile.h b/src/core/compile.h
index 1b5a5bfb..646692c2 100644
--- a/src/core/compile.h
+++ b/src/core/compile.h
@@ -34,7 +34,7 @@
 #define JANET_FUN_APPLY 3
 #define JANET_FUN_YIELD 4
 #define JANET_FUN_RESUME 5
-#define JANET_FUN_GET 6
+#define JANET_FUN_IN 6
 #define JANET_FUN_PUT 7
 #define JANET_FUN_LENGTH 8
 #define JANET_FUN_ADD 9
diff --git a/src/core/corelib.c b/src/core/corelib.c
index 196db895..389c3f6a 100644
--- a/src/core/corelib.c
+++ b/src/core/corelib.c
@@ -262,6 +262,61 @@ static Janet janet_core_setdyn(int32_t argc, Janet *argv) {
     return argv[1];
 }
 
+static Janet janet_core_get(int32_t argc, Janet *argv) {
+    janet_arity(argc, 2, 3);
+    Janet ds = argv[0];
+    Janet key = argv[1];
+    Janet dflt = argc == 3 ? argv[2] : janet_wrap_nil();
+    JanetType t = janet_type(argv[0]);
+    switch (t) {
+        default:
+            return dflt;
+        case JANET_STRING:
+        case JANET_SYMBOL:
+        case JANET_KEYWORD: {
+            if (!janet_checkint(key)) return dflt;
+            int32_t index = janet_unwrap_integer(key);
+            if (index < 0) return dflt;
+            const uint8_t *str = janet_unwrap_string(ds);
+            if (index >= janet_string_length(str)) return dflt;
+            return janet_wrap_integer(str[index]);
+        }
+        case JANET_ABSTRACT: {
+            void *abst = janet_unwrap_abstract(ds);
+            JanetAbstractType *type = (JanetAbstractType *)janet_abstract_type(abst);
+            if (!type->get) return dflt;
+            return (type->get)(abst, key);
+        }
+        case JANET_ARRAY:
+        case JANET_TUPLE: {
+            if (!janet_checkint(key)) return dflt;
+            int32_t index = janet_unwrap_integer(key);
+            if (index < 0) return dflt;
+            if (t == JANET_ARRAY) {
+                JanetArray *a = janet_unwrap_array(ds);
+                if (index >= a->count) return dflt;
+                return a->data[index];
+            } else {
+                const Janet *t = janet_unwrap_tuple(ds);
+                if (index >= janet_tuple_length(t)) return dflt;
+                return t[index];
+            }
+        }
+        case JANET_TABLE: {
+            JanetTable *flag = NULL;
+            Janet ret = janet_table_get_ex(janet_unwrap_table(ds), key, &flag);
+            if (flag == NULL) return dflt;
+            return ret;
+        }
+        case JANET_STRUCT: {
+            const JanetKV *st = janet_unwrap_struct(ds);
+            Janet ret = janet_struct_get(st, key);
+            if (janet_checktype(ret, JANET_NIL)) return dflt;
+            return ret;
+        }
+    }
+}
+
 static Janet janet_core_native(int32_t argc, Janet *argv) {
     JanetModule init;
     janet_arity(argc, 1, 2);
@@ -685,6 +740,14 @@ static const JanetReg corelib_cfuns[] = {
         JDOC("(slice x &opt start end)\n\n"
              "Extract a sub-range of an indexed data strutrue or byte sequence.")
     },
+    {
+        "get", janet_core_get,
+        JDOC("(get ds key &opt dflt)\n\n"
+             "Get the value mapped to key in data structure ds, and return dflt or nil if not found. "
+             "Similar to get, but will not throw an error if the key is invalid for the data structure "
+             "unless the data structure is an abstract type. In that case, the abstract type getter may throw "
+             "an error.")
+    },
     {NULL, NULL, NULL}
 };
 
@@ -960,8 +1023,8 @@ JanetTable *janet_core_env(JanetTable *replacements) {
                          "will be returned to the last yield in the case of a pending fiber, or the argument to "
                          "the dispatch function in the case of a new fiber. Returns either the return result of "
                          "the fiber's dispatch function, or the value from the next yield call in fiber."));
-    janet_quick_asm(env, JANET_FUN_GET,
-                    "get", 3, 2, 3, 4, get_asm, sizeof(get_asm),
+    janet_quick_asm(env, JANET_FUN_IN,
+                    "in", 3, 2, 3, 4, get_asm, sizeof(get_asm),
                     JDOC("(get ds key &opt dflt)\n\n"
                          "Get a value from any associative data structure. Arrays, tuples, tables, structs, strings, "
                          "symbols, and buffers are all associative and can be used with get. Order structures, name "
diff --git a/src/core/math.c b/src/core/math.c
index d6e05a94..3182eadb 100644
--- a/src/core/math.c
+++ b/src/core/math.c
@@ -27,19 +27,131 @@
 #include "util.h"
 #endif
 
+static Janet janet_rng_get(void *p, Janet key);
+
+static void janet_rng_marshal(void *p, JanetMarshalContext *ctx) {
+    JanetRNG *rng = (JanetRNG *)p;
+    janet_marshal_int(ctx, (int32_t) rng->a);
+    janet_marshal_int(ctx, (int32_t) rng->b);
+    janet_marshal_int(ctx, (int32_t) rng->c);
+    janet_marshal_int(ctx, (int32_t) rng->d);
+    janet_marshal_int(ctx, (int32_t) rng->counter);
+}
+
+static void janet_rng_unmarshal(void *p, JanetMarshalContext *ctx) {
+    JanetRNG *rng = (JanetRNG *)p;
+    rng->a = (uint32_t) janet_unmarshal_int(ctx);
+    rng->b = (uint32_t) janet_unmarshal_int(ctx);
+    rng->c = (uint32_t) janet_unmarshal_int(ctx);
+    rng->d = (uint32_t) janet_unmarshal_int(ctx);
+    rng->counter = (uint32_t) janet_unmarshal_int(ctx);
+}
+
+static JanetAbstractType JanetRNG_type = {
+    "core/rng",
+    NULL,
+    NULL,
+    janet_rng_get,
+    NULL,
+    janet_rng_marshal,
+    janet_rng_unmarshal,
+    NULL
+};
+
+static JANET_THREAD_LOCAL JanetRNG janet_vm_rng = {0};
+
+JanetRNG *janet_default_rng(void) {
+    return &janet_vm_rng;
+}
+
+void janet_rng_seed(JanetRNG *rng, uint32_t seed) {
+    rng->a = seed + 123573u;
+    rng->b = (seed + 43234283u) % 12391233u;
+    rng->c = 0x17af0931u;
+    rng->d = 0xFFFaaFFFu;
+    rng->counter = 0u;
+}
+
+uint32_t janet_rng_u32(JanetRNG *rng) {
+    /* Algorithm "xorwow" from p. 5 of Marsaglia, "Xorshift RNGs" */
+    uint32_t t = rng->d;
+    uint32_t const s = rng->a;
+    rng->d = rng->c;
+    rng->c = rng->b;
+    rng->b = s;
+    t ^= t >> 2;
+    t ^= t << 1;
+    t ^= s ^ (s << 4);
+    rng->a = t;
+    rng->counter += 362437;
+    return t + rng->counter;
+}
+
+double janet_rng_double(JanetRNG *rng) {
+    uint32_t hi = janet_rng_u32(rng);
+    uint32_t lo = janet_rng_u32(rng);
+    uint64_t big = (uint64_t)(lo) | (((uint64_t) hi) << 32);
+    return ldexp((big >> (64 - 52)), -52);
+}
+
+static Janet cfun_rng_make(int32_t argc, Janet *argv) {
+    janet_arity(argc, 0, 1);
+    uint32_t seed = (uint32_t)(argc == 1 ? janet_getinteger(argv, 0) : 0);
+    JanetRNG *rng = janet_abstract(&JanetRNG_type, sizeof(JanetRNG));
+    janet_rng_seed(rng, seed);
+    return janet_wrap_abstract(rng);
+}
+
+static Janet cfun_rng_uniform(int32_t argc, Janet *argv) {
+    janet_fixarity(argc, 1);
+    JanetRNG *rng = janet_getabstract(argv, 0, &JanetRNG_type);
+    return janet_wrap_number(janet_rng_double(rng));
+}
+
+static Janet cfun_rng_int(int32_t argc, Janet *argv) {
+    janet_arity(argc, 1, 2);
+    JanetRNG *rng = janet_getabstract(argv, 0, &JanetRNG_type);
+    if (argc == 1) {
+        uint32_t word = janet_rng_u32(rng) >> 1;
+        return janet_wrap_integer(word);
+    } else {
+        int32_t max = janet_getinteger(argv, 1);
+        if (max <= 0) return janet_wrap_number(0);
+        uint32_t modulo = (uint32_t) max;
+        uint32_t bad = UINT32_MAX % modulo;
+        uint32_t word;
+        do {
+            word = janet_rng_u32(rng);
+        } while (word > UINT32_MAX - bad);
+        word >>= 1;
+        return janet_wrap_integer(word % modulo);
+    }
+}
+
+static const JanetMethod rng_methods[] = {
+    {"uniform", cfun_rng_uniform},
+    {"int", cfun_rng_int},
+    {NULL, NULL}
+};
+
+static Janet janet_rng_get(void *p, Janet key) {
+    (void) p;
+    if (!janet_checktype(key, JANET_KEYWORD)) janet_panicf("expected keyword method");
+    return janet_getmethod(janet_unwrap_keyword(key), rng_methods);
+}
+
 /* Get a random number */
 static Janet janet_rand(int32_t argc, Janet *argv) {
     (void) argv;
     janet_fixarity(argc, 0);
-    double r = (rand() % RAND_MAX) / ((double) RAND_MAX);
-    return janet_wrap_number(r);
+    return janet_wrap_number(janet_rng_double(&janet_vm_rng));
 }
 
 /* Seed the random number generator */
 static Janet janet_srand(int32_t argc, Janet *argv) {
     janet_fixarity(argc, 1);
     int32_t x = janet_getinteger(argv, 0);
-    srand((unsigned) x);
+    janet_rng_seed(&janet_vm_rng, (uint32_t) x);
     return janet_wrap_nil();
 }
 
@@ -108,7 +220,7 @@ static const JanetReg math_cfuns[] = {
     {
         "math/seedrandom", janet_srand,
         JDOC("(math/seedrandom seed)\n\n"
-             "Set the seed for the random number generator. 'seed' should be an "
+             "Set the seed for the random number generator. 'seed' should be "
              "an integer.")
     },
     {
@@ -201,6 +313,24 @@ static const JanetReg math_cfuns[] = {
         JDOC("(math/atan2 y x)\n\n"
              "Return the arctangent of y/x. Works even when x is 0.")
     },
+    {
+        "math/rng", cfun_rng_make,
+        JDOC("(math/rng &opt seed)\n\n"
+             "Creates a Psuedo-Random number generator, with an optional seed. "
+             "The seed should be an unsigned 32 bit integer. "
+             "Do not use this for cryptography. Returns a core/rng abstract type.")
+    },
+    {
+        "math/rng-uniform", cfun_rng_uniform,
+        JDOC("(math/rng-seed rng seed)\n\n"
+             "Extract a random number in the range [0, 1) from the RNG.")
+    },
+    {
+        "math/rng-int", cfun_rng_int,
+        JDOC("(math/rng-int rng &opt max)\n\n"
+             "Extract a random random integer in the range [0, max] from the RNG. If "
+             "no max is given, the default is 2^31 - 1.")
+    },
     {NULL, NULL, NULL}
 };
 
diff --git a/src/core/run.c b/src/core/run.c
index 6e09ede0..ab7cee2b 100644
--- a/src/core/run.c
+++ b/src/core/run.c
@@ -55,8 +55,13 @@ int janet_dobytes(JanetTable *env, const uint8_t *bytes, int32_t len, const char
                     done = 1;
                 }
             } else {
-                janet_eprintf("compile error in %s: %s\n", sourcePath,
-                              (const char *)cres.error);
+                if (cres.macrofiber) {
+                    janet_eprintf("compile error in %s: ", sourcePath);
+                    janet_stacktrace(cres.macrofiber, janet_wrap_string(cres.error));
+                } else {
+                    janet_eprintf("compile error in %s: %s\n", sourcePath,
+                                  (const char *)cres.error);
+                }
                 errflags |= 0x02;
                 done = 1;
             }
diff --git a/src/core/value.c b/src/core/value.c
index 4063a26d..e6c4d75d 100644
--- a/src/core/value.c
+++ b/src/core/value.c
@@ -145,6 +145,16 @@ int janet_compare(Janet x, Janet y) {
     return (janet_type(x) < janet_type(y)) ? -1 : 1;
 }
 
+static int32_t getter_checkint(Janet key, int32_t max) {
+    if (!janet_checkint(key)) goto bad;
+    int32_t ret = janet_unwrap_integer(key);
+    if (ret < 0) goto bad;
+    if (ret >= max) goto bad;
+    return ret;
+bad:
+    janet_panicf("expected integer key in range [0, %d), got %v", max, key);
+}
+
 /* Gets a value and returns. Can panic. */
 Janet janet_get(Janet ds, Janet key) {
     Janet value;
@@ -160,56 +170,28 @@ Janet janet_get(Janet ds, Janet key) {
             break;
         case JANET_ARRAY: {
             JanetArray *array = janet_unwrap_array(ds);
-            int32_t index;
-            if (!janet_checkint(key))
-                janet_panic("expected integer key");
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index >= array->count) {
-                value = janet_wrap_nil();
-            } else {
-                value = array->data[index];
-            }
+            int32_t index = getter_checkint(key, array->count);
+            value = array->data[index];
             break;
         }
         case JANET_TUPLE: {
             const Janet *tuple = janet_unwrap_tuple(ds);
-            int32_t index;
-            if (!janet_checkint(key))
-                janet_panic("expected integer key");
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index >= janet_tuple_length(tuple)) {
-                value = janet_wrap_nil();
-            } else {
-                value = tuple[index];
-            }
+            int32_t len = janet_tuple_length(tuple);
+            value = tuple[getter_checkint(key, len)];
             break;
         }
         case JANET_BUFFER: {
             JanetBuffer *buffer = janet_unwrap_buffer(ds);
-            int32_t index;
-            if (!janet_checkint(key))
-                janet_panic("expected integer key");
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index >= buffer->count) {
-                value = janet_wrap_nil();
-            } else {
-                value = janet_wrap_integer(buffer->data[index]);
-            }
+            int32_t index = getter_checkint(key, buffer->count);
+            value = janet_wrap_integer(buffer->data[index]);
             break;
         }
         case JANET_STRING:
         case JANET_SYMBOL:
         case JANET_KEYWORD: {
             const uint8_t *str = janet_unwrap_string(ds);
-            int32_t index;
-            if (!janet_checkint(key))
-                janet_panic("expected integer key");
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index >= janet_string_length(str)) {
-                value = janet_wrap_nil();
-            } else {
-                value = janet_wrap_integer(str[index]);
-            }
+            int32_t index = getter_checkint(key, janet_string_length(str));
+            value = janet_wrap_integer(str[index]);
             break;
         }
         case JANET_ABSTRACT: {
@@ -356,7 +338,7 @@ void janet_putindex(Janet ds, int32_t index, Janet value) {
                 janet_buffer_ensure(buffer, index + 1, 2);
                 buffer->count = index + 1;
             }
-            buffer->data[index] = janet_unwrap_integer(value);
+            buffer->data[index] = (uint8_t)(janet_unwrap_integer(value) & 0xFF);
             break;
         }
         case JANET_TABLE: {
@@ -382,11 +364,8 @@ void janet_put(Janet ds, Janet key, Janet value) {
             janet_panicf("expected %T, got %v",
                          JANET_TFLAG_ARRAY | JANET_TFLAG_BUFFER | JANET_TFLAG_TABLE, ds);
         case JANET_ARRAY: {
-            int32_t index;
             JanetArray *array = janet_unwrap_array(ds);
-            if (!janet_checkint(key)) janet_panicf("expected integer key, got %v", key);
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index == INT32_MAX) janet_panicf("bad integer key, got %v", key);
+            int32_t index = getter_checkint(key, INT32_MAX - 1);
             if (index >= array->count) {
                 janet_array_setcount(array, index + 1);
             }
@@ -394,11 +373,8 @@ void janet_put(Janet ds, Janet key, Janet value) {
             break;
         }
         case JANET_BUFFER: {
-            int32_t index;
             JanetBuffer *buffer = janet_unwrap_buffer(ds);
-            if (!janet_checkint(key)) janet_panicf("expected integer key, got %v", key);
-            index = janet_unwrap_integer(key);
-            if (index < 0 || index == INT32_MAX) janet_panicf("bad integer key, got %v", key);
+            int32_t index = getter_checkint(key, INT32_MAX - 1);
             if (!janet_checkint(value))
                 janet_panicf("can only put integers in buffers, got %v", value);
             if (index >= buffer->count) {
diff --git a/src/core/vm.c b/src/core/vm.c
index d04ac5ff..9daa521d 100644
--- a/src/core/vm.c
+++ b/src/core/vm.c
@@ -1171,6 +1171,8 @@ int janet_init(void) {
     /* Initialize registry */
     janet_vm_registry = janet_table(0);
     janet_gcroot(janet_wrap_table(janet_vm_registry));
+    /* Seed RNG */
+    janet_rng_seed(janet_default_rng(), 0);
     return 0;
 }
 
diff --git a/src/include/janet.h b/src/include/janet.h
index 08264941..9b6f1a32 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -316,6 +316,7 @@ typedef struct JanetView JanetView;
 typedef struct JanetByteView JanetByteView;
 typedef struct JanetDictView JanetDictView;
 typedef struct JanetRange JanetRange;
+typedef struct JanetRNG JanetRNG;
 typedef Janet(*JanetCFunction)(int32_t argc, Janet *argv);
 
 /* Basic types for all Janet Values */
@@ -927,6 +928,11 @@ struct JanetRange {
     int32_t end;
 };
 
+struct JanetRNG {
+    uint32_t a, b, c, d;
+    uint32_t counter;
+};
+
 /***** END SECTION TYPES *****/
 
 /***** START SECTION OPCODES *****/
@@ -1103,6 +1109,11 @@ JANET_API void janet_debug_find(
     JanetFuncDef **def_out, int32_t *pc_out,
     const uint8_t *source, int32_t line, int32_t column);
 
+/* RNG */
+JANET_API JanetRNG *janet_default_rng(void);
+JANET_API void janet_rng_seed(JanetRNG *rng, uint32_t seed);
+JANET_API uint32_t janet_rng_u32(JanetRNG *rng);
+
 /* Array functions */
 JANET_API JanetArray *janet_array(int32_t capacity);
 JANET_API JanetArray *janet_array_n(const Janet *elements, int32_t n);
diff --git a/test/suite7.janet b/test/suite7.janet
index e482e1b4..d5a8834c 100644
--- a/test/suite7.janet
+++ b/test/suite7.janet
@@ -193,4 +193,19 @@
 # Trim empty string
 (assert (= "" (string/trim " ")) "string/trim regression")
 
+# RNGs
+
+(defn test-rng
+  [rng]
+  (assert (all identity (seq [i :range [0 1000]]
+                             (<= (math/rng-int rng i) i))) "math/rng-int test")
+  (assert (all identity (seq [i :range [0 1000]]
+    (def x (math/rng-uniform rng))
+    (and (>= x 0) (< x 1))))
+          "math/rng-uniform test"))
+
+(def seedrng (math/rng 123))
+(for i 0 75
+  (test-rng (math/rng (:int seedrng))))
+
 (end-suite)