diff --git a/examples/3sum.dst b/examples/3sum.dst
index 831c95a4..57027f13 100644
--- a/examples/3sum.dst
+++ b/examples/3sum.dst
@@ -1,16 +1,13 @@
-(import examples.iterators :as "")
-
 (defn sum3
  "Solve the 3SUM problem in O(n^2) time."
  [s]
  (def tab @{})
  (def solutions @{})
  (def len (length s))
- (for [k 0 len]
+ (loop [k :range [0 len]]
   (put tab (get s k) k))
- (for [i 0 len]
-  (for [j 0 len]
+ (loop [i :range [0 len], j :range [0 len]]
    (def k (get tab (- 0 (get s i) (get s j))))
    (when (and k (not= k i) (not= k j) (not= i j))
-    (put solutions {i true j true k true} true))))
- (iter2array (map (fn [x] (iter2array (keys x))) (keys solutions))))
+    (put solutions {i true j true k true} true)))
+ (map keys (keys solution)))
diff --git a/examples/fizzbuzz.dst b/examples/fizzbuzz.dst
index 17686e7d..8187bbaf 100644
--- a/examples/fizzbuzz.dst
+++ b/examples/fizzbuzz.dst
@@ -3,7 +3,7 @@
 (defn fizzbuzz
  "Prints the fizzbuzz problem."
  []
- (for [i 1 101]
+ (loop [i :range [1 101]]
   (let [fizz (zero? (% i 3))
         buzz (zero? (% i 5))]
     (print (cond
diff --git a/examples/frequencies.dst b/examples/frequencies.dst
index df66a4d5..b9d35eb6 100644
--- a/examples/frequencies.dst
+++ b/examples/frequencies.dst
@@ -4,7 +4,8 @@
  "Get the number of occurences of each value in a indexed structure."
  [ind]
  (def freqs @{})
- (each (fn [x] 
-    (let [n (get freqs x)]
-     (put freqs x (if n (+ 1 n) 1)))) ind)
+ (loop 
+   [x :in ind]
+   (def n (get freqs x))
+   (put freqs x (if n (+ 1 n) 1)))
  freqs)
diff --git a/examples/hello.dst b/examples/hello.dst
index b27f5127..cad00e8f 100644
--- a/examples/hello.dst
+++ b/examples/hello.dst
@@ -1,3 +1,5 @@
 # Prints hello
 
+(import examples.3sum)
+
 (print "hello, world!")
diff --git a/examples/primes.dst b/examples/primes.dst
index f47757b3..03e6facd 100644
--- a/examples/primes.dst
+++ b/examples/primes.dst
@@ -4,10 +4,10 @@
  "Returns a list of prime numbers less than n."
  [n]
  (def list @[])
- (for [i 2 n]
+ (loop [i :range [2 n]]
   (var isprime? true)
   (def len (length list))
-  (for [j 0 len]
+  (loop [j :range [0 len]]
    (def trial (get list j))
    (if (zero? (% i trial)) (:= isprime? false)))
   (if isprime? (array.push list i)))
diff --git a/src/compiler/boot.dst b/src/compiler/boot.dst
index 3d241b37..09a3135f 100644
--- a/src/compiler/boot.dst
+++ b/src/compiler/boot.dst
@@ -218,18 +218,63 @@ value."
   (array.concat accum body)
   (apply1 tuple accum))
 
+(defmacro loop
+  "A general purpose loop macro."
+  [head & body]
+  (def head1 (ast.unwrap1 head))
+  (def len (length head1))
+  (defn doone
+    [i]
+    (if (>= i len)
+      (tuple.prepend body 'do)
+      (do
+        (def bindings (get head1 i))
+        (def verb (ast.unwrap1 (get head1 (+ i 1))))
+        (def object (ast.unwrap1 (get head1 (+ i 2))))
+        (switch verb
+          :range (do
+                 (def [start end _inc] (ast.unwrap1 object))
+                 (def inc (if _inc _inc 1))
+                 (def endsym (gensym))
+                 (tuple 'do
+                        (tuple 'var bindings start)
+                        (tuple 'def endsym end)
+                        (tuple 'while (tuple < bindings endsym)
+                               (doone (+ i 3))
+                               (tuple ':= bindings (tuple + bindings inc)))))
+          :keys (do
+                  (def $dict (gensym "dict"))
+                  (tuple 'do
+                         (tuple 'def $dict object)
+                         (tuple 'var bindings (tuple next $dict nil))
+                         (tuple 'while (tuple not= nil bindings)
+                                (doone (+ i 3))
+                                (tuple ':= bindings (tuple next $dict bindings)))))
+          :in (do
+                (def $len (gensym "len"))
+                (def $i (gensym "i"))
+                (def $indexed (gensym "indexed"))
+                (tuple 'do
+                       (tuple 'def $indexed object)
+                       (tuple 'def $len (tuple length $indexed))
+                       (tuple 'var $i 0)
+                       (tuple 'while (tuple < $i $len)
+                              (tuple 'def bindings (tuple get $indexed $i))
+                              (doone (+ i 3))
+                              (tuple ':= $i (tuple + 1 $i)))))
+          (error ("unexpected loop verb: " verb))))))
+  (doone 0))
+
 (defmacro for
- "An imperative for loop over an integer range. Use with caution and discretion."
- [head & body]
-  (def [sym start end _inc] (ast.unwrap1 head))
-  (def inc (if _inc _inc 1))
-  (def endsym (gensym))
+  "Similar to loop, but accumulates the loop body into an array and returns that."
+  [head & body]
+  (def $accum (gensym "accum"))
   (tuple 'do
-    (tuple 'var sym start)
-    (tuple 'def endsym end)
-    (tuple 'while (tuple < sym endsym)
-     (tuple.prepend body 'do)
-     (tuple ':= sym (tuple + sym inc)))))
+         (tuple 'def $accum @[])
+         (tuple 'loop head 
+           (tuple array.push $accum
+                (tuple.prepend body 'do)))
+         $accum))
 
 (defmacro and
  "Evaluates to the last argument if all preceding elements are true, otherwise
@@ -332,7 +377,7 @@ Returns nil if args is empty."
  (def len (length args))
  (when (pos? len)
   (var ret (get args 0))
-  (for [i 0 len]
+  (loop [i :range [0 len]]
    (def v (get args i))
    (if (order v ret) (:= ret v)))
   ret))
@@ -356,7 +401,7 @@ Returns nil if args is empty."
    [a lo hi by]
    (def pivot (get a hi))
    (var i lo)
-   (for [j lo hi]
+   (loop [j :range [lo hi]]
     (def aj (get a j))
     (when (by aj pivot)
      (def ai (get a i))
@@ -391,8 +436,8 @@ Returns nil if args is empty."
 an indexed type (array, tuple) with a function to produce a value."
  [f init ind]
  (var res init)
- (for [i 0 (length ind)]
-  (:= res (f res (get ind i))))
+ (loop [x :in ind]
+  (:= res (f res x)))
  res)
 
 (defn map
@@ -402,19 +447,19 @@ the same type as the input sequence."
  (def ninds (length inds))
  (if (= 0 ninds) (error "expected at least 1 indexed collection."))
  (var limit (length (get inds 0)))
- (for [i 0 ninds]
+ (loop [i :range [0 ninds]]
   (def l (length (get inds i)))
   (if (< l limit) (:= limit l)))
  (def [i1 i2 i3 i4] inds)
  (def res (array.new limit))
  (switch ninds
-  1 (for [i 0 limit] (array.push res (f (get i1 i))))
-  2 (for [i 0 limit] (array.push res (f (get i1 i) (get i2 i))))
-  3 (for [i 0 limit] (array.push res (f (get i1 i) (get i2 i) (get i3 i))))
-  4 (for [i 0 limit] (array.push res (f (get i1 i) (get i2 i) (get i3 i) (get i4 i))))
-  (for [i 0 limit]
+  1 (loop [i :range [0 limit]] (array.push res (f (get i1 i))))
+  2 (loop [i :range [0 limit]] (array.push res (f (get i1 i) (get i2 i))))
+  3 (loop [i :range [0 limit]] (array.push res (f (get i1 i) (get i2 i) (get i3 i))))
+  4 (loop [i :range [0 limit]] (array.push res (f (get i1 i) (get i2 i) (get i3 i) (get i4 i))))
+  (loop [i :range [0 limit]]
    (def args (array.new ninds))
-   (for [j 0 ninds] (array.push args (get (get inds j) i)))
+   (loop [j :range [0 ninds]] (array.push args (get (get inds j) i)))
    (array.push res (apply1 f args))))
  res)
 
@@ -425,18 +470,18 @@ return a new indexed type."
  (def ninds (length inds))
  (if (= 0 ninds) (error "expected at least 1 indexed collection."))
  (var limit (length (get inds 0)))
- (for [i 0 ninds]
+ (loop [i :range [0 ninds]]
   (def l (length (get inds i)))
   (if (< l limit) (:= limit l)))
  (def [i1 i2 i3 i4] inds)
  (switch ninds
-  1 (for [i 0 limit] (f (get i1 i)))
-  2 (for [i 0 limit] (f (get i1 i) (get i2 i)))
-  3 (for [i 0 limit] (f (get i1 i) (get i2 i) (get i3 i)))
-  4 (for [i 0 limit] (f (get i1 i) (get i2 i) (get i3 i) (get i4 i)))
-  (for [i 0 limit]
+  1 (loop [i :range [0 limit]] (f (get i1 i)))
+  2 (loop [i :range [0 limit]] (f (get i1 i) (get i2 i)))
+  3 (loop [i :range [0 limit]] (f (get i1 i) (get i2 i) (get i3 i)))
+  4 (loop [i :range [0 limit]] (f (get i1 i) (get i2 i) (get i3 i) (get i4 i)))
+  (loop [i :range [0 limit]]
    (def args (array.new ninds))
-   (for [j 0 ninds] (array.push args (get (get inds j) i)))
+   (loop [j :range [0 ninds]] (array.push args (get (get inds j) i)))
    (apply1 f args))))
 
 (defn mapcat
@@ -445,8 +490,8 @@ use array to concatenate the results. Returns the same
 type as the input sequence."
  [f ind t]
  (def res @[])
- (for [i 0 (length ind)]
-  (array.concat res (f (get ind i))))
+ (loop [x :in ind]
+  (array.concat res (f x)))
  (if (= :tuple (type (or t ind)))
   (apply1 tuple res)
   res))
@@ -455,10 +500,8 @@ type as the input sequence."
  "Given a predicate, take only elements from an array or tuple for
 which (pred element) is truthy. Returns the same type as the input sequence."
  [pred ind t]
- (def len (length ind))
- (def res (array.new len))
- (for [i 0 len]
-  (def item (get ind i))
+ (def res @[])
+ (loop [item :in ind]
   (if (pred item)
    (array.push res item)))
  (if (= :tuple (type (or t ind)))
@@ -469,7 +512,7 @@ which (pred element) is truthy. Returns the same type as the input sequence."
   "Create an array of values [0, n)."
   [n]
   (def arr (array.new n))
-  (for [i 0 n] (put arr i i))
+  (loop [i :range [0 n]] (put arr i i))
   arr)
 
 (defn find-index
@@ -521,19 +564,18 @@ the predicate, and abort on first failure."
 
 (defn juxt*
   [& funs]
-  (def len (length funs))
   (fn [& args]
    (def ret @[])
-   (for [i 0 len]
-    (array.push ret (apply1 (get funs i) args)))
+   (loop [f :in funs]
+    (array.push ret (apply1 f args)))
    (apply1 tuple ret)))
 
 (defmacro juxt
  [& funs]
  (def parts @['tuple])
  (def $args (gensym))
- (for [i 0 (length funs)]
-  (array.push parts (tuple apply1 (get funs i) $args)))
+ (loop [f :in funs]
+  (array.push parts (tuple apply1 f $args)))
  (tuple 'fn (tuple '& $args) (apply1 tuple parts)))
 
 (defmacro ->
@@ -611,7 +653,7 @@ in the same manner, and so on. Useful for expressing pipelines of data."
   (def lk (length keys))
   (def lv (length vals))
   (def len (if (< lk lv) lk lv))
-  (for [i 0 len]
+  (loop [i :range [0 len]]
    (put res (get keys i) (get vals i)))
   (if (= :struct t)
     (table.to-struct res)
@@ -631,18 +673,15 @@ in the same manner, and so on. Useful for expressing pipelines of data."
    collection"
   [& colls]
   (def container @{})
-  (for [i 0 (length colls)]
-   (def c (get colls i))
-   (var key (next c nil))
-   (while (not= nil key)
-     (put container key (get c key))
-     (:= key (next c key))))
+  (loop [c :in colls
+        key :keys c]
+       (put container key (get c key)))
   (if (table? (get colls 0)) container (table.to-struct container)))
 
 (defn keys
  "Get the keys of an associative data structure."
  [x]
- (def arr @[])
+ (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
   (array.push arr k)
@@ -652,7 +691,7 @@ in the same manner, and so on. Useful for expressing pipelines of data."
 (defn values
  "Get the values of an associative data structure."
  [x]
- (def arr @[])
+ (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
   (array.push arr (get x k))
@@ -662,7 +701,7 @@ in the same manner, and so on. Useful for expressing pipelines of data."
 (defn pairs
  "Get the values of an associative data structure."
  [x]
- (def arr @[])
+ (def arr (array.new (length x)))
  (var k (next x nil))
  (while (not= nil k)
   (array.push arr (tuple k (get x k)))
@@ -706,12 +745,12 @@ to call on any table. Does not print table prototype information."
    (def len (length y))
    (if (< len 5)
     (do
-     (for [i 0 len]
+     (loop [i :range [0 len]]
       (when (not= i 0) (buffer.push-string buf " "))
       (recur (get y i))))
     (do
       (buffer.push-string indent "  ")
-      (for [i 0 len]
+      (loop [i :range [0 len]]
        (when (not= i len) (buffer.push-string buf indent))
        (recur (get y i)))
       (buffer.popn indent 2)
@@ -719,9 +758,7 @@ to call on any table. Does not print table prototype information."
 
   (defn pp-dict-nested [y]
    (buffer.push-string indent "  ")
-   (def ps (sort (pairs y)))
-   (for [i 0 (length ps)]
-    (def [k v] (get ps i))
+   (loop [[k v] :in (sort (pairs y))]
     (buffer.push-string buf indent)
     (recur k)
     (buffer.push-string buf " ")
@@ -730,10 +767,9 @@ to call on any table. Does not print table prototype information."
    (buffer.push-string buf indent))
 
   (defn pp-dict-simple [y]
-   (def ps (sort (pairs y)))
-   (for [i 0 (length ps)]
-    (def [k v] (get ps i))
-    (if (pos? i) (buffer.push-string buf " "))
+   (var i -1)
+   (loop [[k v] :in (sort (pairs y))]
+    (if (pos? (++ i)) (buffer.push-string buf " "))
     (recur k)
     (buffer.push-string buf " ")
     (recur v)))
@@ -772,11 +808,7 @@ to call on any table. Does not print table prototype information."
  [x]
 
  (defn doarray [a]
-  (def len (length a))
-  (def newa @[])
-  (for [i 0 len]
-   (array.push newa (macroexpand-1 (get a i))))
-  newa)
+   (map macroexpand-1 a))
 
  (defn dotable [t]
   (def newt @{})
@@ -891,7 +923,7 @@ onvalue."
       (buffer.clear buf)
       (chunks buf p)
       (:= len (length buf))
-      (for [i 0 len]
+      (loop [i :range [0 len]]
         (fiber.yield (get buf i))))
    0))
 
@@ -943,15 +975,13 @@ onvalue."
    (pp x))
  (when f
   (def st (fiber.stack f))
-  (def len (length st))
-  (for [i 0 len]
-   (def {
+  (loop [{
     :function func
     :tail tail
     :pc pc
     :c c
     :name name
-   } (get st i))
+   } :in st]
    (file.write stdout "  in")
    (when c (file.write stdout " cfunction"))
    (when name (file.write stdout (string " " name)))
@@ -1067,7 +1097,8 @@ returned from compiling and running the file."
  (while k
   (def v (get newenv k))
   (when (not (get v :private))
-   (put env (symbol prefix k) v))
+    (def newv (table.setproto @{:private true} v))
+   (put env (symbol prefix k) newv))
   (:= k (next newenv k))))
 
 (defmacro import [path & args]
diff --git a/src/compiler/compile.c b/src/compiler/compile.c
index a7f2e5bd..c7f09657 100644
--- a/src/compiler/compile.c
+++ b/src/compiler/compile.c
@@ -830,7 +830,6 @@ recur:
                                     DstSignal status = dst_call(f, dst_tuple_length(tup) - 1, tup + 1, &x);
                                     dst_gcunlock(lock);
                                     if (status != DST_SIGNAL_OK) {
-                                        printf("Status: %d\n", status);
                                         const uint8_t *es = dst_formatc("error in macro expansion: %V", x);
                                         dstc_error(c, ast, es);
                                     }
diff --git a/src/core/string.c b/src/core/string.c
index de3ff201..043b62a9 100644
--- a/src/core/string.c
+++ b/src/core/string.c
@@ -885,6 +885,47 @@ static int cfun_checkset(DstArgs args) {
     DST_RETURN_TRUE(args);
 }
 
+static int cfun_join(DstArgs args) {
+    const Dst *parts;
+    const uint8_t *joiner;
+    uint8_t *buf, *out;
+    int32_t joinerlen, partslen, finallen, i;
+    DST_MINARITY(args, 1);
+    DST_MAXARITY(args, 2);
+    DST_ARG_INDEXED(parts, partslen, args, 0);
+    if (args.n == 2) {
+        DST_ARG_BYTES(joiner, joinerlen, args, 1);
+    } else {
+        joiner = NULL;
+        joinerlen = 0;
+    }
+    /* Check args */
+    finallen = 0;
+    for (i = 0; i < partslen; i++) {
+        const uint8_t *chunk;
+        int32_t chunklen = 0;
+        if (!dst_chararray_view(parts[i], &chunk, &chunklen)) {
+            DST_THROW(args, "expected string|symbol|buffer");
+        }
+        if (i) finallen += joinerlen;
+        finallen += chunklen;
+    }
+    out = buf = dst_string_begin(finallen);
+    for (i = 0; i < partslen; i++) {
+        const uint8_t *chunk = NULL;
+        int32_t chunklen = 0;
+        if (i) {
+            memcpy(out, joiner, joinerlen);
+            out += joinerlen;
+        }
+        dst_chararray_view(parts[i], &chunk, &chunklen);
+        memcpy(out, chunk, chunklen);
+        out += chunklen;
+    }
+    DST_RETURN_STRING(args, dst_string_end(buf));
+
+}
+
 static const DstReg cfuns[] = {
     {"string.slice", cfun_slice},
     {"string.repeat", cfun_repeat},
@@ -899,6 +940,7 @@ static const DstReg cfuns[] = {
     {"string.replace-all", cfun_replaceall},
     {"string.split", cfun_split},
     {"string.check-set", cfun_checkset},
+    {"string.join", cfun_join},
     {NULL, NULL}
 };
 
diff --git a/src/include/dst/dst.h b/src/include/dst/dst.h
index 626326db..9f79ef55 100644
--- a/src/include/dst/dst.h
+++ b/src/include/dst/dst.h
@@ -274,6 +274,13 @@ int dst_typeabstract_err(DstArgs args, int32_t n, const DstAbstractType *at);
     }\
 } while (0)
 
+#define DST_ARG_INDEXED(DESTVALS, DESTLEN, A, N) do {\
+    if ((A).n <= (N)) return dst_typemany_err(A, N, DST_TFLAG_INDEXED);\
+    if (!dst_seq_view((A).v[(N)], &(DESTVALS), &(DESTLEN))) {\
+        return dst_typemany_err(A, N, DST_TFLAG_INDEXED);\
+    }\
+} while (0)
+
 #define _DST_ARG(TYPE, NAME, DEST, A, N) do { \
     DST_CHECK(A, N, TYPE);\
     DEST = dst_unwrap_##NAME((A).v[(N)]); \